  Man is one of those organisms in on on which a whole host of parasites find conditions suitable for their existence: Protozoa, Platyhelminthes, Nematoda, Acanthocephala, Hirudinea, and a large number of Arthropoda (Arachnida as well as Insects) all include members which are parasites of man. These animals either live on the external surface of the body or within the intestine and its appendages. Other organs and systems are not quite free from foreign organisms—we are acquainted with parasites in the skeletal system, in the circulatory system, in the brain, in the muscles, in the excretory and genital organs, and even in the organs of sense. It is possible, and perhaps might be advantageous, to arrange and describe the parasites of man according to the situations in which they are found (parasites of the skin, intestinal parasites, etc.). Their description in the various stages of development would, however, be disturbed when, as is generally the case, the different stages are passed in different organs, and a work which treats more fully of the natural history of the parasites than of the local disorders to which they give rise would suffer thereby. It is, therefore, preferable to describe the parasites of man in their systematic order, and to mention their different situations in man in describing each species. A. PROTOZOA, | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| At 24°C. | At 37°C. | |
| Salivary glands | Negative | Positive |
| Malpighian tubules | Positive | Positive |
| Gut and contents | Positive | Positive |
| Excrement | Positive | Positive |
| Genital organs | Positive | Positive |
Coxal fluid is usually negative; thick, white excrement from Malpighian tubes is positive.
When the ticks were incubated at 21° to 24°C. no spirochÆtes, as such, were seen in the organs, except perhaps in the gut, where they often disappeared in a few days. When the ticks were previously incubated at 35° to 37°C. for two to three days, spirochÆtes, as such, reappear in the gut, organs and hÆmocoelic fluid. The infection proceeds, not from the salivary gland, but from the infective excrement, that is, from the thick, white material voided by the tick while feeding, usually towards the end of the meal. This Malpighian excrement passes into the wound caused by the bite, being greatly aided by the clear and more limpid coxa fluid, which bathes the under surface of the tick’s body, and mixes with and carries the infective excrement into the wound. Ticks remain infective for a long time.
Fig. 55.—SpirochÆta duttoni and its coccoid bodies in the tick (O. moubata).—Mononuclear cells of the tick (O. moubata) containing (a) SpirochÆte breaking up into coccoid bodies; (b) Similar tick-cell containing coccoid bodies or granules. Such mononuclear cells occur in various organs of ticks and in developing Malpighian tubules. (Original. From preparations by Fantham.)
The spirochÆtes in the gut of infected ticks divide by a process of multiple transverse fission into granules, which are composed of chromatin (fig.54). These granules—sometimes known as coccoid bodies—are capable of multiplication. Leishman first found them in clumps inside the cells of the Malpighian tubules (cf. fig.55).
To summarize, when spirochÆtes are ingested by a tick, some of them pass through the gut-wall into the hÆmocoelic (body) fluid. They then bore their way into the cells of various organs (fig.55a)
Schuberg and Manteufel have found that certain O. moubata, perhaps 30 per cent. of the specimens of a given neighbourhood, may acquire a natural active immunity against infection with S. duttoni.
S. duttoni, or a closely allied form (by some termed S. novyi), occurs in Colombia, and is spread by the tick Ornithodorus turicata. In Panama a similar spirochÆte is probably spread by O. talaje.
SpirochÆta gallinarum, Stephens and Christophers, 1905
(= SpirochÆta marchouxi, Nuttall, 1905).
This SpirochÆte, which occurs in fowls and is pathogenic, is transmitted by the tick Argas persicus. It is about 10µ to 20µ long. There is a pathogenic spirochÆte known to occur in geese, named by Sakharoff (1891) S. anserina, and found in Caucasia. This may be the same as S. gallinarum, in which case the name S. anserina will have priority. These organisms cause fever, diarrhoea, anÆmia and death. The life history of the avian pathogenic spirochÆtes has been studied by Balfour, by Hindle150 and by Fantham.151 It is essentially similar to that of S. duttoni.
Marchoux and Couvy152 (1913) consider that the “fragmentation of the chromatin” in spirochÆtes is a process of degeneration. Working with A. persicus and S. gallinarum, they state that a large number of the spirochÆtes ingested by the Argas almost immediately pass through the wall of the alimentary canal and appear in the hÆmocoelic fluid. Marchoux and Couvy consider that Leishman’s granules may be found in the Malpighian tubules of various Arachnids. They found spirochÆtes in the cephalic glands of infected Argas. They consider that spirochÆtes remain as wavy spirochÆtes within the tick, if they are to be infective, though the spirochÆtes may become so thin as to be invisible! The latter argument is obviously weak, and it was never asserted that all granules in the Malpighian tubules of infected ticks were derived from spirochÆtes. With dark-ground
SpirochÆta recurrentis, Lebert, 1874.
Syn.: SpirochÆta obermeieri, Cohn, 1875.
This organism was discovered by Obermeier (1873) in cases of relapsing fever in Berlin. Short forms 7µ to 9µ long, and longer (probably adult) forms, 16µ to 19µ, are found in the blood. The width is 0·25µ. Parasites 12µ or 13µ long are often observed.
The spirochÆte is found in the blood during febrile attacks and relapses, but not during intervening periods. It can be inoculated into monkeys, rats and mice. It can live in the bed-bug, Cimex lectularius, and Nuttall has succeeded in transmitting S. recurrentis from mouse to mouse by the bites of the same bug. The French investigators Sergent and Foley (1908–9) in Algeria, and Nicolle, Blaizot and Conseil (1912) in Tunis, have shown experimentally that S. recurrentis (var. berbera) is transmitted by lice. The latter workers also demonstrated the method of infection that commonly occurs, namely, by the scratching of the skin and crushing of lice containing spirochÆtes on the excoriated surface of the body.
Lice as transmitting agents for relapsing fever were indicated by Mackie154 in 1907. An epidemic among Indian school children furnished the materials.155 It was noted that out of 170 boys, 137 were infected, and the boys were very verminous. Among the girls, 35 out of 114 suffered, and few lice were found on them. Twenty-four per cent. of the lice taken from the boys contained spirochÆtes as compared with 3 per cent. of those from the girls. As the epidemic died out among the boys, the lice also became fewer, and an increase in the number of cases among the girls coincided with an increase in the number of lice. SpirochÆtes were found in the gut, Malpighian tubules and genital organs of the lice. Mackie thought that infection of the patients was brought about by the regurgitation of the spirochÆtes when the lice fed, but proof of this was lacking.
In 1912, Nicolle, Blaizot and Conseil,156 working in Tunis and using chiefly an Algerian strain of relapsing fever spirochÆtes (sometimes called S. berbera), showed by direct experiments that infection by means of the bites of Pediculus vestimenti and P. capitis was untenable. As many as 4,707 infected lice were fed on one man, and 6,515 on another occasion were allowed to bite a man after they had fed on a monkey heavily infected with spirochÆtes, yet no infection of the man followed. Examination of the lice showed that the spirochÆtes left the gut soon after they were ingested, and
It was noted that the irritation due to the lice caused scratching, and that thereby lice became crushed on to the skin. An emulsion was made of two infected lice and rubbed on to the slightly excoriated skin of one of the above workers. Infection followed five days later. A drop of emulsion placed on the conjunctiva of the human eye produced spirochÆtosis after an incubation of seven days. The body contents of such lice, then, produce infection when they reach the blood by any excoriated or penetrable surface. The stages leading up to infection in nature briefly are: The irritation due to the louse bites causes scratching, and the lice are crushed on to the skin. The slight abrasion is quite sufficient to permit the entry of the parasite. The louse bite alone is harmless. Infection by way of the eye is quite probable in Africa, remembering the constant trouble due to sand, dust, insects, etc., resulting in frequent touching of the eyes.
The spirochÆtes occur in the body fluid of the lice and can pass in it to the adjacent organs. Thus they probably find their way into the genital organs, and into the eggs of the lice. Eggs laid twenty to thirty days after the parent became infected have retained the infection, and the larvÆ issuing from such eggs must have contained some form of spirochÆtes, for an emulsion of either the eggs or the larvÆ produced spirochÆtosis when inoculated into monkeys. Further details regarding the spirochÆtosis in the eggs of the lice and in the larvÆ are needed. Hereditary infection, however, has been demonstrated, but is not very common. Sergent and Foley (1914) state that the spirochÆte possesses a very small and virulent form which it assumes during apyrexial periods in man and during a period following an infecting meal in the louse. Nicolle and Blanc (1914) find that the organisms are infective in the louse just before they reappear as spirochÆtes. Nicolle and Blaizot found that female lice were more susceptible to spirochÆtes than males, four times as many females as males being infected.
Tictin (1897) found S. recurrentis in bugs recently fed on patients, and infected a monkey with the fluids of crushed bugs. Karlinski (1902) found the spirochÆtes in bed-bugs in infected houses. There is some other evidence to show that bugs may transmit the spirochÆte in Nature. Further researches are needed regarding the relationship of bed-bugs and human spirochÆtosis.
Multiplication of S. recurrentis is by longitudinal and transverse division (including so-called “incurvation”), and the organism forms small, ovoid bodies (“coccoid” bodies) in the same way as S. duttoni.
S. recurrentis is the cause of European relapsing fever, and a number of possible varieties of it are associated with relapsing fevers in other parts of the world. Such spirochÆtes only differ by biological reactions, such as acquired immunity tests. They include:—
S. rossii, the agent of East African relapsing fever; S. novyi, the agent of North American relapsing fever; S. carteri, the agent of Indian relapsing fever; S. berbera, the agent of North African and Egyptian relapsing fever.
Other Human SpirochÆtes are:—
S. schaudinni. This organism, according to Prowazek, is the agent of ulcus tropicum. It varies in length from 10µ to 20µ.
S. aboriginalis has been found in cases of granuloma inguinale in British New Guinea and Western Australia. It also occurs in dogs, and may not be truly parasitic.
S. vincenti. This spirochÆte is 12µ to 25µ in length, tapers at both ends and has few coils. It has been associated with angina vincenti. It often occurs in company with fusiform bacilli.
S. bronchialis, found by Castellani in 1907 in cases of bronchitis in Ceylon. The parasites are delicate, but show morphological variation. This organism is important and has since been found in the West Indies, India, Philippine Islands and various parts of Africa, such as the Anglo-Egyptian Sudan, Uganda and West Africa. It has recently been the subject of research by Chalmers and O’Farrell, Taylor, and Fantham.
S. phagedenis was found by Noguchi in a ten days old ulcerated swelling of the labium. The organism shows much variation in size, being 4µ to 30µ in length.
S. refringens (Schaudinn, 1905) occurs in association with Treponema pallidum in syphilitic lesions, but is non-pathogenic. It is 20µ to 35µ long and 0·5µ to 0·75µ broad, being larger than T. pallidum and more easily stained.
Various spirochÆtes have also been notified in vomits, chiefly in Australia; others from the human intestinal tract, e.g., S. eurygyrata; S. stenogyrata (Werner); S. hachaizÆ (Kowalski), in cholera motions; S. buccalis (Cohn, 1875) and S. dentium occurring in the human mouth and in carious teeth (S. dentium, Koch, 1877, being the smaller); S. acuminata and S. obtusa found by Castellani in open sores in cases of yaws.
Animal spirochÆtes of economic importance include:—
S. anserina, highly pathogenic to geese.
S. gallinarum (= S. marchouxi) in fowls. (See p.119.)
S. theileri in cattle and S. ovina in sheep also occur in Africa; their pathogenicity is not clear.
S. laverani (= S. muris), occurring in the blood of and pathogenic
Numerous spirochÆtes have been recorded from the guts of various mammals, birds, fishes, amphibia and insects.
Cultivation of SpirochÆtes.—Cultures of spirochÆtes have been made with little success or with great difficulty until comparatively recently, when Noguchi (1912) devised a means whereby he has cultivated most of the pathogenic spirochÆtes as well as some Treponemata.
Noguchi has now cultivated S. duttoni, S. recurrentis, S. rossii, S. novyi and S. gallinarum from the blood; S. phagedenis157 from human phagedÆnic lesions; S. refringens158 and spirochÆtes from the teeth.
His method is as follows:—
A piece of fresh, sterile tissue, usually rabbit kidney, is placed in a sterile test-tube. A few drops of citrated blood from the heart of an infected animal, e.g., rat or mouse, is added, and about 15c.c. of sterile ascitic or hydrocoele fluid is poured quickly into the tube. Some of the tubes are covered with a layer of sterile paraffin oil, others are left uncovered. The tubes are incubated at 37°C. The best results are obtained if the blood is taken from an animal forty-eight to seventy-two hours after it has been inoculated, that is, before the spirochÆtes reach their maximum multiplicative period in the blood. The presence of some oxygen seems indispensable for these blood spirochÆtes, and they fail to develop in vacuo or in an atmosphere of hydrogen.
For subcultures, 0·5c.c. of a culture is added to the medium instead of citrated blood, and it is useful to add a little fresh, normal blood, either human or from an animal, such as a rat.
Noguchi found that the events in cultures were:—
S. duttoni,159 maximum multiplication on the eighth to ninth day; disintegration beginning on the tenth day, spirochÆtes disappeared after about the fifteenth day. No diminution of virulence was found at the ninth day.
S. rossii (= S. kochi).160 Maximum development on the ninth day, after which the virulence diminishes. The incubation period is also prolonged.
S. recurrentis161 (= S. obermeieri). Maximum growth on the seventh day.
S. novyi.162—Maximum development on the seventh day. It is more difficult to grow than the preceding forms.
All the above spirochÆtes showed undoubted longitudinal division and transverse division was observed in part.
S. gallinarum163 can be cultivated as above, but transverse division
Treponemata.
The genus Treponema (Schaudinn, 1905), includes minute, thread-like organisms, with spirally coiled bodies, the spirals being preformed or fixed. No membrane or crista is present, according to Schaudinn, though a slight one is said by Blanchard to be present in the organism of yaws. The ends of the organisms are tapering and pointed. Multiplication is by longitudinal and transverse division. The most important members of the genus are T. pallidum, the agent of syphilis, and T. pertenue, which is responsible for framboesia or yaws.
Treponema pallidum, Schaudinn, 1905.
Syn.: SpirochÆta pallida.
Treponema pallidum was first described by Schaudinn and Hoffmann in 1905 under the name of SpirochÆta pallida. It has also been described under the names of Spironema pallida, Microspironema pallida and Trypanosoma luis. Siegel in 1905 described an organism which he called Cytorhyctes luis and considered to be the agent of syphilis. Schaudinn reinvestigated Siegel’s work and found T. pallidum, which he considered to be the causal agent of the disease, and pronounced against Cytorhyctes luis. It is probable now that both workers were correct, for Balfour (1911) has seen the emission of minute granules or “coccoid” bodies from T. pallidum and these granules probably correspond to the C. luis of Siegel. Recently E.H. Ross, having observed a spirochÆte stage in the development of Kurloff bodies, thinks that T. pallidum is a stage in the life-history of a Lymphocytozoon. MacDonagh has also described a complicated and somewhat similar cycle, but these observations require further study and confirmation.
Fig. 56.—Treponema pallidum. (After Bell, from Castellani and Chalmers.)
T. pallidum varies from 4µ to 10µ in length, its average length being 7µ, while its width is usually about 0·25µ. Longer individuals
The Treponemata occur in the primary and secondary sores, but are difficult to find in the tertiary eruptions of syphilis. Noguchi and Moore (1913) and Mott164 (1913) have demonstrated T. pallidum in the brain in cases of general paralysis of the insane. Marie and Levaditi (1914), however, consider that the treponeme found in the brain in such cases is different from T. pallidum.
Cultivation of T. pallidum.—This has been accomplished successfully by Noguchi,165 using a modification of his method for spirochÆte cultivation, for T. pallidum is much more difficult to grow than spirochÆtes, being a strict anaerobe.
Fig. 57.—Diagram of apparatus for cultivation of Treponema pallidum by Noguchi’s method. (After Noguchi.)
The apparatus consists of two glass tubes, the upper being connected to the lower by a narrower tube passing through a rubber cork (fig.57). Both tubes are carefully sterilized.
A piece of fresh, sterile rabbit’s kidney is placed in the lower tube, which is filled with ascitic fluid, or ascitic fluid and bouillon mixture. The tube is inoculated with syphilitic material and corked by inserting the upper tube. In the bottom of the upper tube a piece of sterile rabbit’s kidney is placed and syphilitic material poured over it. A mixture of one part ascitic fluid and two parts of slightly alkaline agar is then poured over the tissue and allowed to solidify. When solid, a layer of sterile paraffin oil is poured on top of it, and the top plugged with cotton wool (fig.57). The whole is then incubated at 37°C. for two or three weeks. The tissue removes traces of oxygen from the lower levels of the medium and also probably
The syphilitic material for culture is prepared by cutting off pieces of tissue from the lesions, washing in sterile salt solution containing 1 per cent. sodium citrate, and then emulsifying the tissue in a mortar with sodium citrate.
Good cultures show rapid multiplication, which is invariably by longitudinal division.
In his various cultivation experiments Noguchi166 found morphological and pathogenic variations in T. pallidum. Three forms of the organism were found, namely, thicker, average and thinner types. The lesions caused in the testicle of the rabbit differ according to the variety inoculated, but more work is necessary on the subject.
Noguchi167 has cultivated a separate organism, T. calligyrum, from the surface of human genital or anal lesions, either syphilitic or non-syphilitic. It is apparently non-pathogenic, and is 6µ to 14µ long.
Hata (1913)168 has modified the Noguchi technique for the cultivation of spirochÆtes and treponemes, with a view to simplification and convenience. Hata substitutes normal horse serum for ascitic fluid and the “buffy coat” of the clot of horse blood in place of the small pieces of rabbit’s kidney. It is unnecessary to place sterile paraffin on the surface of the medium.
The horse serum is mixed with twice its volume of physiological saline solution. The mixture is placed in tubes which are heated on a water-bath at 58°C., the temperature being raised gradually until it reaches 70° or 71°C. in three hours. The tubes are then heated at 71°C. for half an hour. After cooling, the contents will consist of an opaque semi-coagulated mass. This semi-coagulated serum and saline mixture may be substituted for Noguchi’s ascitic fluid.
The buff coagulum is cut into small pieces, about 1c.c. in volume. They must be forced with a sterile glass rod to the bottom of the semi-coagulated serum and saline mixture. The medium is inoculated with a small quantity of infected blood and kept at 37°C. In the case of S. recurrentis, growth of spirochÆtes is observed on the second day, reaching a maximum in five to seven days. The growth of the organisms proceeds rather more slowly, they live for a longer period and maintain their virulence better than in Noguchi’s medium.
Treponema pertenue, Castellani, 1905.
Syn.: SpirochÆta pertenuis; S. pallidula, Castellani, 1905.
Castellani discovered the organism in 1905, in scrapings of yaws pustules. He first described it under the name of SpirochÆta pertenuis.
Fig. 58.—Treponema pertenue. (After Castellani and Chalmers.)
Treponema pertenue (fig.58), though delicate and slender, shows great morphological variation both in length and thickness. It may be short, e.g., 7µ, but can attain 18µ to 20µ in length and may be even larger. In cultures made by Noguchi, thick, medium and thin forms were found, each giving rise to a different type of framboesial lesion when inoculated into the testicles of rabbits, thus suggesting the possibility of the occurrence of varieties of T. pertenue.
The organism is difficult to stain, but occasionally deeper staining granules are found along its body. They may represent a diffuse nucleus. Granule formation similar to that of T. pallidum has been observed by Ranken, using dark-ground illumination.
Many experiments have been made with a view to establishing the identity of the organism of yaws and also of differentiating between the causative agents of yaws and syphilis. Both monkeys and the human subject have been experimentally inoculated with yaws material and have developed the disease.
In an early experiment, negroes were inoculated with the secretion from lesions of yaws. All of them developed the disease, nodules appearing, chiefly at the seat of inoculation, in from twelve to twenty days, followed by the usual eruption. Similar results were obtained with thirty-two Chinese prisoners, who were inoculated with yaws, twenty-eight becoming infected.
A naturally infected yaws patient when inoculated with syphilis, contracted that infection, thus showing that yaws does not confer immunity to syphilis. This has also been observed naturally, when yaws patients have contracted syphilis.
Experiments with monkeys have been successfully performed. The incubation period varies from sixteen to ninety-two days. Lesions appear first at the seat of inoculation, and in some monkeys the eruption is localized to this spot, though the infection is general, T. pertenue occurring in the spleen, lymphatics, etc. Monkeys inoculated with splenic blood of a yaws patient, and also sometimes with blood from the general circulation, have become infected.
Castellani and others have shown that monkeys successfully inoculated with syphilis do not become immune to yaws, and vice-versÂ.
Craig and Ashburn, using the monkey Cynomolgus philippinensis, found these animals susceptible to yaws but not to syphilis.
The ulcerated lesions of framboesia are rapidly invaded by numerous bacteria as well as by different spirochÆtes, of which Castellani has described three distinct species. One is identical with SpirochÆta refringens, Schaudinn, the other two are thin and delicate. One, S. obtusa, has blunt ends; the other S. acuminata, has pointed ends. T. pertenue is also present.
The reasons for considering T. pertenue to be the specific cause of framboesia are:—
(1) T. pertenue is the only organism present in non-ulcerated papules, in the spleen and in the lymphatics of yaws patients, or of monkeys artificially infected with the disease. By no method has any other organism been obtained.
(2) Extract of framboesia material, free from all organisms other than T. pertenue, reproduces the disease if inoculated.
(3) Extract of framboesia material deprived by filtration of T. pertenue is no longer infective on inoculation.
The method of infection is contaminative, by direct contact. Women in Ceylon are frequently infected by their children. Any slight skin abrasion is sufficient to admit the parasite. In some cases, insects may carry the disease from person to person, and even in hospitals, when dressings are removed, it has been noticed that flies greedily suck the secretion from the ulcers. T. pertenue has been recovered from flies that have fed on yaws, and monkeys have contracted the disease when flies were placed and retained on them for a short time, after the insects had fed on yaws material.
Cultivation.—T. pertenue has been cultivated by Noguchi, who finds three types of parasites in his cultures, as before mentioned. Its multiplication is by longitudinal division.
Noguchi169 (1912), has cultivated species of Treponema from the human mouth, e.g., T. macrodentium, T. microdentium and T. mucosum, the latter from pyorrhea alveolaris. These parasites in the past may have been confused under the name SpirochÆta dentium.
Class III. SPOROZOA, Leuckart, 1879.
The third group of the Protozoa consists entirely of parasitic organisms forming the class known as the Sporozoa or spore-producing animals. The members of this class are characterized
The Sporozoa are widely distributed, occurring in various tissues and organs of Annelids, Molluscs, Arthropods, and Vertebrates. Their food, which is fluid, is absorbed osmotically. The life-cycle of a SporozoÖn may be completed within one host or may be distributed between two different hosts.
The Sporozoa were divided by Schaudinn into two groups or sub-classes, called (1) the Telosporidia, and (2) the Neosporidia.
The Telosporidia are Sporozoa in which the reproductive phase of the parasites is distinct from the growing or trophic phase, and follows after it. The Neosporidia include Sporozoa in which growth and spore-formation go on simultaneously. This classification is not final, for certain exceptions and difficulties are already known with regard to it. It is possible that the class Sporozoa is not a natural entity, but should be replaced by two classes of equal rank, corresponding in most respects with the Telosporidia and Neosporidia.
The Telosporidia comprise the Gregarinida, the Coccidiidea, and the HÆmosporidia. Doflein combines the two latter orders into one known as the Coccidiomorpha.
The Neosporidia comprise the Myxosporidia, the Microsporidia, the Actinomyxidia, the Sarcosporidia, and the Haplosporidia. Doflein combines the first three orders into one, the Cnidosporidia.
Sub-Class. TELOSPORIDIA, Schaudinn.
Sporozoa in which the reproductive phases follow completion of growth.
Order. Gregarinida, AimÉ Schneider emend. Doflein.
Fig. 59.—Monocystis agilis from seminal vesicles of Lumbricus ×250. (After Stein.)
Knowledge of the Gregarinida probably goes back as far as the year 1684, when Redi observed gregarines in the crab, Cancer pagurus. Von Cavolini (1787) found them in Cancer depressus. The name Gregarina was created by L. Dufour (1828), who observed masses of these organisms in the gut of insects of different orders. Hammerschmidt (1838) and von Siebold found rich infestations in insects, while Dujardin (1835) and Henle described various genera from segmented worms. Henle (1835) also observed cysts containing “navicellÆ” in the sperm-sacs of segmented worms, and attention was drawn to his researches by the discovery by von Siebold (1839) of “pseudonavicellÆ” in the gut of Sciara nitidicollis. Up to this time many workers considered the gregarines to be worms, but KÖlliker (1845) investigated many of them and maintained their unicellular nature, while Stein’s work (1848) showed the interrelation of the pseudonavicellÆ and the gregarines.
From 1873 onwards AimÉ Schneider made important additions to the knowledge of the morphology, life-history, and systematic position of numerous gregarines. BÜtschli (1881) and L. LÉger (1892) also contributed much work on the subject. The discoveries of Schaudinn with regard to the life-cycle of Coccidia gave a fresh stimulus to the study of the Gregarines, whereby the life-cycles of numerous forms and the phases thereof have been elucidated.
Asexual multiplication is not common among the Gregarines, but is known to occur in the sub-order Schizogregarinea, formerly known as the Amoebosporidia.
Although the Gregarinida are not known to be parasitic in man or other vertebrates, they are of great interest, inasmuch as they are among the earliest known Sporozoa, and therefore will be briefly described here.
Fig. 60.—Gregarina longa from larva of crane-fly (Tipula). a, in epithelial cell of host; b, c, gradually leaving host-cell; d, adhering to host-cell; e, fully developed free trophozoite.
Fig. 61.—Xyphorhynchus firmus with epimerite in intestinal epithelial cell of host. (After LÉger.)
The Gregarines are usually elongate, somewhat flattened organisms (figs.59, 60), whose bodies are enclosed in an elastic and often thick cuticle. The enclosed living substance shows a separation into ectoplasm and endoplasm, as is common among Protozoa. The cuticle is sometimes regarded as the outer portion or epicyte of the ectoplasm. A single, vesicular, spherical, or elliptical, large nucleus, with its chromatin concentrated to form a spherical karyosome, is present. The body of some gregarines may be divided by ingrowing ectoplasmic partitions or septa, and are then said to be “septate” or “polycystid” (fig.61). Other gregarines remain simple and non-septate, and are termed “monocystid” (fig.59). The monocystid gregarines occur especially in the body cavity of ChÆtopoda and Insecta, more rarely in Echinodermata, in the parenchyma of Platyhelminthes,
The ectoplasm of a gregarine exhibits three layers: (1) An epicyte (cuticle) externally of which the epimerite is composed; (2) a sarcocyte which forms the septa if present; (3) the deeper myocyte layer containing contractile elements in the form of fibrils or threads termed myonemes (fig.62).
Fig. 62.—Gregarina munieri (from the beetle, Chrysomela hÆmoptera). Section through surface layers. Cu, cuticle; E, ectoplasm proper; G, gelatinous layer; My, myonemes in myocyte layer. ×1500. (After Schewiakoff.)
The endoplasm is fluid and granular, containing many enclosures, which are of the nature of reserve food materials. They consist of fat droplets or of paraglycogen, and give the organisms an opaque appearance. Lithocystis contains crystals of calcium oxalate in its endoplasm.
Many gregarines are capable of active movements, though they do not possess obvious locomotor organs. The movement is of a smooth, gliding character and two suggestions have been put forward to explain it. According to Schewiakoff, a gelatinous substance is secreted between the layers of the ectoplasm. This is extruded posteriorly and thus the animal is pushed forward. On the other hand, Crawley considers that the movements are produced by contractions of the myonemes.
Occasionally, temporary associations of gregarines are formed by a number of individuals adhering to one another end to end. Such temporary associations are examples of syzygy. Such syzygies must not be confused with true associations which form an essential part of the life-cycle.
Fig. 63.—Monocystis agilis. Spores from vesicula seminalis of the Earthworm. a, Sporoblast with single nucleus, enclosed in sporocyst; b, mature spore containing sporozoites; c, diagrammatic cross-section of spore, showing eight sporozoites round residual protoplasm. (After BÜtschli.)
The life-cycle of a relatively simple gregarine, such as Monocystis agilis (fig.59), parasitic in earthworms, may now be considered. The gregarines, being members of the Sporozoa, produce spores at one phase of the life-cycle. Each gregarine spore (fig.63) develops within itself a number of minute, sickle-shaped or vermicular bodies, known as sporozoites or primary infecting germs. Eight sporozoites are often formed within each spore. When absorbed by a new host, the spore softens and the sporozoites issue from it. They are capable of active movement and may or may not enter a cell, such as one of those of the digestive tract, or, as in Monocystis, a cell lining the vesicula seminalis which becomes a sperm-cell aggregate (sperm morula). When the sporozoite has reached the place of its choice in the host it ceases active movements and proceeds to feed passively on the fluid substances around it, whether they be those of tissues or body fluids. This passive, growing and feeding form is known as the trophozoite. After a trophic existence of longer or shorter duration, the trophozoite ceases to feed and prepares for reproduction. Two trophozoites associate together, each of them first becoming somewhat rounded. The two trophozoites, now known as sporonts or gametocytes, become invested in a single common envelope or cyst (fig.64, a). The nucleus of each gametocyte then divides by a series of binary fissions (fig.64, b), and the daughter nuclei thus produced arrange themselves at the periphery of the parent cells (fig.64, c). Cytoplasm collects around each of these nuclei, and thus a number of gametes are formed within each gametocyte. The gametes for a time exhibit active movements, and ultimately ripe gametes of different parentage fuse in pairs, that is, conjugation occurs (fig.64, d). In this way zygotes are produced, the nucleus of each zygote being formed by the fusion of two gamete nuclei.
Fig. 64.—Schematic figures of conjugation and spore formation in Gregarines. For details see text. (After Calkins and Siedlecki, modified.)
Fig. 65.—Stylorhynchus oblongatus. a, cyst containing two sporonts or gametocytes, each full of gametes, those in the upper one being male. b, ripe male and female gametes. ×1,600. (After L. LÉger.)
The zygote grows slightly and becomes oval or elongate, and at this period is often called the sporoblast. It then secretes an external
It will be noticed that in the above life-cycle no asexual multiplication occurs. These organisms, such as Monocystis, are known as the Eugregarines, and include the majority of the gregarines. The remainder, which have introduced schizogony into their life-cycle, are known as the Schizogregarines.
Fig. 66.—Spores of various Gregarines. a, Xiphorhynchus. b, Ancyrophora. c, Gonospora. d, Ceratospora. (After LÉger.)
There are variations in the morphology and life-cycle of gregarines besides those that have been mentioned. It is not within the scope of this book to discuss them in detail, but the following may be noted:—
Morphological differentiation of gametes may occur as in Stylorhynchus oblongatus (fig.65), which differentiation is probably of a sexual nature.
The sporocyst really consists of two layers, an epispore and an endospore. Externally the spores of different gregarines show great variety in shape and markings, and spines, or long processes may be present (fig.66).
The resistant spores serve for the transmission of the gregarines from host to host. The mode of infection is contaminative, the spores expelled with the dejecta of one host being absorbed with the food of a new host.
The Gregarinida may be classified as follows:—
Sub-order I.—Eugregarinea, without schizogony.
Tribe 1.—Acephalina.—Without an epimerite and non-septate; often “coelomic” (body-cavity) parasites. E.g.: Monocystis, with
Tribe 2.—Cephalina.—With an epimerite, either temporarily or permanently, in the trophic phase. Usually septate (except DoliocystidÆ). Many families, genera and species. Common in the digestive tracts of insects. E.g.: Gregarina, with several species, Gregarina ovata in the earwig, Gregarina blattarum in the cockroach, Stylorhynchus in beetles, Pterocephalus in centipedes, etc.
Sub-order II.—Schizogregarinea, with schizogony.
Tribe 1.—Endoschiza.170—With schizogony occurring in the intracellular phase, e.g., Selenidium (from Annelida and Gephyrea), Merogregarina (from an Ascidian).
Tribe 2.—Ectoschiza.—In which the schizont is free, and schizogony is extracellular, e.g., Ophryocystis (from Blaps, a beetle), and Schizocystis (from Ceratopogon larva).
Order. Coccidiidea.
Hake (1839) first saw the organisms now termed Coccidia during his investigations on the so-called coccidial nodules of rabbits. The opinions as to the nature of these peculiar formations were very diverse. The discoverer considered them to be a sort of pus corpuscle; Nasse (1843) took them for epithelial cells of the biliary passages, others for helminthes, especially the ova of trematodes (Dujardin, KÜchenmeister, Gubler, etc). Remak (1845) was the first to draw attention to their relation to the Psorospermia (Myxosporidia), and this investigator found them also in the small intestine and vermiform appendix of rabbits. LieberkÜhn (1854), who examined not only the coccidia of rabbits, but found similar forms in the kidneys of frogs, likewise called them definitely psorosperms. To differentiate MÜller’s psorosperms, which are found in fishes, from those of rabbits, etc., the latter were called egg-shaped psorosperms (Eimer), until R. Leuckart (1879) named them Coccidia and placed them in a group of the Sporozoa analogous to that of the Gregarinida, Myxosporidia, etc. Numerous works confirmed the occurrence of coccidia, not only in all classes of vertebrate animals, but also in invertebrates (Mollusca, Myriapoda, Annelida, etc.). A large number of genera and species have in the course of time been described which inhabit the epithelium of the intestine and its appendages for choice, but are also found in other organs (kidneys, spleen, ovaries, vas deferens, testicles). Some also live in the connective tissue of various organs, more particularly of the intestine.
The knowledge of the development of the coccidia was of particular importance in determining their classification. By means of encysted coccidia from the liver of rabbits, Kauffmann (1847) first confirmed the fact that the cyst, which was partly or entirely filled with granular contents, divided into three or four pale bodies (fig.71) after a long sojourn in water. LieberkÜhn observed the same process in the host in the case of the coccidia of the kidney of the frog. Stieda (1865) studied more minutely the changes that occur within the encysted coccidia of the liver of rabbits after the death of the host. He discovered that the bodies now known as “spores” were oval formations pointed at one pole, and surrounded by a delicate membrane, which exhibited a certain thickness at the pointed extremity and enclosed a slightly bent rodlet, expanding at either end into a strongly light-refracting globule; a finely granular globule was present in the middle of the spore. Waldenburg (1862) saw the
According to the discovery of Kloss (1855), the spores of the coccidia of the urinary organ of the garden snail were formed in far greater numbers: the round spores also harboured several (five to six) rodlets, which after the bursting of the spore-envelope became free. Eimer’s researches (1870) afforded information regarding a Coccidium from the intestine of the mouse, which was transformed in toto into a “spore,” containing small sickle-shaped bodies. The fact was, moreover, established that the little bodies left the delicate envelope when in the intestine, made movements of flexion and extension, and were finally transformed into amoeboid organisms, which apparently penetrated the epithelial cells; at all events, similar bodies of various sizes were seen in these cells. Taking the immense number of these parasites into account and the lack of any other cause, Eimer attributed the sudden death of his mice to the Gregarina falciformis, as the parasite was then called, just in the same way as a few years previously Reincke ascribed the acute and fatal intestinal catarrh of rabbits to the invasion of intestinal coccidia.
All that had become known about coccidia up to 1879 was then compiled by Leuckart, and completed by his own observations on the coccidia of the liver of the rabbit. Experimental infections had already been conducted by Waldenburg (1862) with intestinal coccidia of rabbits, and by Rivolta (1869–73) with the coccidia of fowls, which experiments confirmed the importance of the spores, or bodies enclosed in them, in the transmission of the parasites to other animals. Accordingly, it was assumed that after the entry of the spores into the intestine the sporozoites were set free, actively penetrated into the intestinal cells, where they grew into coccidia, and finally became encysted. The further development, i.e., the formation of spores, took place outside the host’s body in these cases; in other cases (Kloss, Eimer) it took place within the host. Although much regarding the cycle of development was still hypothetical, the ideas coincided with the observations, and were therefore universally regarded as established. Further research confirmed this view in numerous new forms.
L. Pfeiffer’s statements (1891) on the part that certain coccidia or their sporozoites played, or seemed to play, as causes of disease gave a renewed impetus to the investigation of the coccidia. The ingestion of even very numerous spores did not appear to account for the mass infection so frequently observed, even after Balbiani had confirmed the fact that there were two, and not one, sporozoites contained in every spore of the coccidia of rabbits (fig.72). The hypothesis was therefore advanced that the sporozoites or young coccidia were able to divide once again by sporulating. The question was finally solved quite differently. R. Pfeiffer (1892) first confirmed the fact that in addition to the well-known method of sporulation in the coccidia of the rabbit that causes the infection of fresh hosts (“exogenous sporulation”), an enormous increase may follow in the already infected host in a manner that Eimer first observed in the coccidia of the intestine of the mouse (“endogenous sporulation”). It had hitherto been believed that some of the species of coccidia increased like the rabbit parasite, then known as Coccidium oviforme, and others like Eimeria falciformis, and this difference had been made the foundation of a classification. R. Pfeiffer was successful in observing the occurrence of both kinds of development in the same species, and expressed the opinion that endogenous sporulation (fig.73), which takes place within the host, was the cause of the mass-infection that is mostly accompanied by serious consequences (fig.74).L. Pfeiffer sought, especially, to demonstrate the correctness of this view as regards other species of coccidia and for this purpose he utilized the experiences already published. Coccidia were known to exist in a number of different hosts, and to propagate in some according
This interpretation of facts was combated especially by A. Schneider (1892) and by LabbÉ, but has, nevertheless, proved true, apart from the circumstance that Schuberg succeeded in discovering the hitherto unknown Coccidium form in the intestine of the mouse; and that, moreover, LÉger confirmed the fact that there are no Arthropoda in which Eimeria are not found together with coccidia. The question was finally settled by experiments made by LÉger with the coccidia of Scolopendra cingulata, by Schaudinn and Siedlecki with those of Lithobius forficatus, and by Simond with the coccidia of the rabbit. On Simond’s suggestion the sickle-shaped germs corresponding to the sporozoites, which are formed by endogenous sporulation, are generally termed merozoites; and in accordance with Schaudinn’s suggestion, those individuals which form merozoites are termed schizonts, and those which produce spores are called sporonts. In contradistinction to sporogony (exogenous sporulation), the term schizogony (endogenous sporulation) is used.
The more minute examination of these processes at last led to the discovery of sexual dimorphism, of copulation and of alternation of generations in the coccidia. Schuberg was the first to consider the possibility of copulation in coccidia; in addition to the formations which now are termed merozoites, he observed very diminutive bodies (“microsporozoites”) in the coccidia of the intestine of the mouse, which were able eventually to copulate. LabbÉ confirmed this observation in some of the species, and Simond expressed the opinion that bodies termed “chromatozoites” occurred in all coccidia. Copulation itself was then observed by Schaudinn and Siedlecki (1897). The copulating bodies were termed gametes. As, however, they differed considerably one from the other, the males were called microgametes (i.e., the microsporozoites of LabbÉ and the chromatozoites of Simond) and the females macrogametes. After copulation was completed sporogony took place, and in the cycle of development of one species this regularly alternated with schizogony (asexual multiplication). Schaudinn in 1900 described in detail the life-cycle of Eimeria (Coccidium) schubergi.
The recognition of this unsuspected complicated process was bound to effect reforms in the classification of the coccidia; and all the forms that had been regarded as developmental stages (Eimeria, etc.) had to be reconsidered.
Occurrence.—The Coccidiidea in their mature condition usually live within the epithelial cells of various organs, and by choice inhabit those of the intestine and of its associated organs. They also occur frequently in the excretory organs of mammals, birds, amphibia, molluscs, arthropods, and may also be found in the testes and vas deferens, but the statement that they live in hen’s eggs, as well as in the oviducts of fowls, has not been confirmed.171 Some species inhabit the nuclei of cells, others live in the connective tissue, but
The size of the Coccidiidea, corresponding as a rule to the capacity of their habitat, is usually small, but there are said to be species that attain a diameter of 1mm. Their form172 is globular, oval, or elliptical. External appendages are lacking, at least during the trophic or vegetative period of their life, which is spent in epithelial cells, within which they increase in size. Frequently one only is present in each cell, but more can occur. The body substance is composed of a more or less finely granular or distinctly alveolar protoplasm which exhibits no differentiation into ecto- and endoplasm. All species possess a nucleus that enlarges with their growth; sometimes it only shows through the cytoplasm as a lighter spot, or may even be quite concealed. It is vesicular, and besides containing very delicate threads of chromatin in the clear nucleoplasm, it contains generally only one large karyosome.
The infected epithelial cells degenerate sooner or later as the parasite feeds on them (fig.67, II-IV). After their form has been changed by the action of the growing parasite, they finally perish. The cell membrane then alone surrounds the coccidia, which, at least in the species sufficiently known, begin to propagate by an asexual process (schizogony), the parasites themselves becoming schizonts, as the initial stage is usually called. They differ from later stages (sporonts or gametocytes), which resemble them in form, by the absence of granulations in the cytoplasm, as well as by the vesicular nucleus. The form is not always the same, for in some cases, at least, many schizonts assume a globular form.
Schizogony (fig.67, V-VII) commences with a division of the nucleus, which takes place in different ways in the various species. This finally leads to the formation of numerous daughter nuclei which become smaller and smaller, and which collect beneath the surface of the schizonts. In some species the daughter nuclei collect only in one half of the schizont. A part of the protoplasm of the periphery now divides around each daughter nucleus, the remaining part (residual body) being left in the centre or on one side. The segments of the divided cytoplasm, each containing a nucleus, assume a fusiform shape and become merozoites, which very soon become free (fig.67, VIII) and leave the residual body. They are distinguishable from the very similar sporozoites (fig.67, I), as the merozoites possess a karyosome.
Fig. 67.—Life-cycle of Eimeria (Coccidium) schubergi, Schaud., from the intestine of Lithobius. (After Schaudinn.) The infection is caused by a cyst (XX), containing spores, which reaches the intestine of a Lithobius, where it discharges the sporozoites (I). II, A sporozoite invading an intestinal epithelial cell; III, intestinal epithelial cell with young trophozoite; IV, intestinal epithelial cell with a globular schizont; V, nuclear segmentation within the schizont; VI, the daughter nuclei arranging themselves superficially; VII, formation of the merozoites; VIII, merozoites that have become free, and which, penetrating into other epithelial cells of the same intestine, repeat the schizogony (II-VIII); IX and X, merozoites which, likewise invading the epithelial cells of the same intestine, become sexually differentiated; xia, young macrogametocyte; XIb, older macrogametocyte; XIc, mature macrogametocyte (discharging particles of chromatin); XIIa, young microgametocyte; XIIb, older microgametocyte; XIIc, increase of nuclei in the microgametocyte; XIId, the globular residual body around which numerous microgametes have formed; XIIe, an isolated microgamete; XIII, the mature macrogamete surrounded by numerous microgametes and forming a cone of reception or fertilization prominence; XIV, shows the nucleus of a microgamete that has penetrated and fused with the nucleus of the macrogamete (fertilization)—the latter forms a membrane and becomes an oÖcyst; XV, XVI, XVII, nuclear segmentation in the oÖcyst; XVIII, oÖcyst with four sporoblasts; XIX, the sporoblasts transformed into spores, each containing two sporozoites; XX, the cyst introduced into the intestine and liberating the sporozoites by bursting.
The merozoites move in a manner similar to that of the sporozoites. The movements consist either of slow incurvations with subsequent straightenings, or annular contractions along the entire extent of the body. In addition, there are gliding movements similar to those of many gregarines, and brought about in a like manner by the secretion at the posterior extremity of a gelatinous substance that hardens rapidly.
The merozoites do not gain the open in the usual way, but are destined to infect still further the same host by actively penetrating into other epithelial cells of the affected organ. Here they continue their growth and may again and again undergo schizogony. In the Infusoria the repeated segmentations finally cease and are renewed only after a conjugation. This is likewise the case with the Coccidia, with the difference that in the latter the two conjugating individuals (gametes) are differently constituted one from the other, whereas in the Infusoria they are almost always similar.
When the schizogony ceases, the merozoites, that had penetrated the epithelial cells and become trophozoites there, consist of two kinds of differently constituted individuals. One kind possesses a clear cytoplasm (fig.67, XII), the other an opaque, richly granular cytoplasm (fig.67, XI), while both possess a vesicular nucleus with a karyosome. In order to continue their development, the more granular individuals must be fertilized, and are therefore termed either female gametes or, on account of their size, macrogametes. The male individuals (microgametes) necessary to conjugation, are formed in greater numbers from the less dense microgametocytes or male mother-cells (fig.67, XIId). They are slender bodies consisting chiefly of nuclear substance, and in most species bear two flagella of unequal length directed backwards, the place of insertion of which varies according to the species (fig.67, XIIe).
While the development of the microgametes is rapidly advancing a change occurs in the nucleus of the female parent forms or macrogametocytes. Parts of the karyosome are extruded (fig.67, XIc), and the nucleus loses at the same time its vesicular form. One macrogamete results, after nuclear maturation, from one macrogametocyte. By this time the macrogametes are capable of conjugation, and the process takes place within the host, generally, however, outside the affected and degenerated host cells. The microgametes that have now become free from the very large residual body, crowd around the mature macrogametes, which often send out a small prominence (“cone of reception” or fertilization protuberance) for their reception (fig.67, XIII). As soon as a microgamete comes in contact with this and penetrates into the cytoplasm of the macrogamete, the latter surrounds itself with a membrane which prevents the intrusion of other microgametes. The nucleus of the microgamete
The reduced nucleus of the macrogamete elongates on the entry of the microgamete, and becomes a fertilization spindle to which the male pronucleus (from the microgamete) becomes attached (fig.67, XIV and XV). Thereupon the spindle divides into two daughter nuclei (fig.67, XVI) which assume a round shape. The protoplasm at this stage may at once divide, or another segmentation of the daughter nuclei may first occur. In the former case the two halves divide again, so that finally four nucleated segments, the sporoblasts, are formed, whereas in the latter case the four sporoblasts appear simultaneously (fig.67, XVII). In both cases a residual body of varying size is separated from the protoplasm of the oÖcyst. As a rule the oÖcysts have already been discharged from the body of the host, and in the manner described above, form the sporoblasts after a longer or shorter period of incubation.
The sporoblasts are originally naked, but each soon secretes a homogeneous membrane, the sporocyst, in which it becomes enveloped (fig.67, XVIII). After the segmentation of the nucleus the contents divide into two sickle-shaped sporozoites, in addition to which there is generally also a residual body (fig.67, XIX).
This terminates the development. The spores are intended for the infection of other hosts. If they reach the intestine of suitable hosts, either free or enclosed in the oÖcyst wall, the action of the intestinal juices causes them to open and permits the escape of the sporozoites (fig.67, XX). The latter move exactly like the merozoites and soon make their way into epithelial cells (fig.67, I), where they become schizonts, and thus repeat the life cycle.
Although our knowledge of the development of the coccidia is but of recent date, yet it already extends to a large number of species, which exhibit various deviations from the cycle of development described above. For instance, in addition to differences in the gametocytes, the schizonts of Adelea and Cyclospora also show differentiation and give rise to macromerozoites and micromerozoites, whilst in Adelea and Klossia a precocious association of the gametocytes precedes the true copulation of the ripe gametes.
The classification of the Coccidiidea is based chiefly on the number of sporozoites found in each spore, and the number of sporocysts (spores) found in one oÖcyst. LÉger173 recognises two great legions, the Eimeridea and the Adeleidea, the former comprising the greater number of genera, including the genus of most economic importance, Eimeria. It must be noted that, though a member of
Certain of the more important of the Coccidiidea may now be considered.
Genus. Eimeria, AimÉ Schneider, 1875.
Syn.: Psorospermium, Rivolta, 1878; Cytospermium, Rivolta, 1878; Coccidium, R. Leuckart, 1879; Pfeifferia, LabbÉ, 1894; Pfeifferella, LabbÉ, 1899.
The Eimeria belong to LÉger’s old family, the TetrasporocystidÆ, which comprises forms producing oÖcysts with four sporocysts, each containing two sporozoites. The cysts are spherical or oval, as are also usually the schizonts. The members of the genus are confined chiefly to vertebrate hosts, the more important economically occurring in mammals and birds. From the mammalian hosts very rarely the parasites may reach man. Eimeria (Coccidium) avium of wild birds and poultry, and Eimeria stiedÆ parasitic in rabbits, may be considered. There is a general similarity in their life-cycles and each is of great practical importance.
Eimeria avium, Silvestrini and Rivolta.
Eimeria avium is responsible for fatal epizoÖtics among game birds such as grouse, pheasants and partridges, and domestic poultry such as fowls, ducks, pigeons and turkeys, and can pass from any one of these hosts to any of the others with the same effect. The organism is parasitic in the alimentary tract of the host, affecting more especially the small intestine (duodenum) and the cÆca, but in some cases penetrating to the liver and multiplying there (as in turkeys), producing necrotic cheesy patches, that ultimately become full of oÖcysts. The gut is rendered very frail by the action of the parasites, its mucous membrane is greatly injured, and is often reduced to an almost structureless pulp, riddled with parasites (fig.68). Infection is conveyed from host to host by the ingestion of food or drink contaminated with the oÖcysts voided in the fÆces of infected birds. Oval oÖcysts from 24µ to 35µ long and from 14µ to 20µ broad are the means of infection. The oÖcysts develop internally four sporocysts or spores, from each of which two sporozoites are produced. The life-history174 presents two phases: (1) The asexual multiplicative phase, schizogony, for the increase in numbers of the parasites within the same host; (2) the reproductive phase, following the formation of gametes (gametogony), leading to the production of resistant oÖcysts, destined for the transference of the parasite to new hosts (sporogony).
The oÖcysts usually reach the duodenum unharmed, with food or drink. Under
Fig. 68.—Small piece of epithelial lining of gut of heavily infected Grouse chick, showing various stages in life history of the parasite Eimeria avium; par, parasite (trophozoite); mz, merozoite; sch, schizont; spz, sporozoite; ooc, oÖcyst; ?, male gametocyte; ?, female gametocyte. ×750. (After Fantham.)
The merozoites of Eimeria avium are arranged “en barillet,” like the segments of an orange (figs.68 mz, 69, G), therein differing from those of E. schubergi, which are arranged “en rosace.” They separate from one another (fig.69, H), penetrate other epithelial cells, where they may, in turn, become schizonts. Eight to fourteen merozoites are usually formed by each schizont, twenty have been found, while in cases of intense infection when space has become limited, the number may be only four.
After a number of generations of merozoites have been formed, a limit is reached both to the multiplicative capacity of the parasite and to the power of the bird to provide the invader with food. Consequently, resistant forms of the parasite are necessary, and the trophozoites begin to show sexual differentiation instead of forming schizonts, that is, gametogony commences.
Fig. 69.—Eimeria avium. Diagram of life-cycle. For explanation see text. (After Fantham.)
Certain trophozoites store food and become large and granular. These are macrogametocytes (fig.69, I, ?). The microgametocytes (fig.69, I, ?) are smaller and far less granular. The macrogametocyte continues to grow, and
The method of infection175 is contaminative, by way of food or drink. Young birds are especially susceptible to infection. Certain birds, particularly older ones, may act as reservoirs of oÖcysts, being continuously infected themselves, without showing any marked ill effects from the parasite, but being highly infectious to other birds. Much moisture retards the development of sporocysts considerably. The duration of vitality of the infective oÖcysts has been determined experimentally to extend well over two years, and in certain cases longer. Eimeria avium is the causal agent of “white diarrhoea” or “white scour” in fowls, and of “blackhead” in turkeys.
Eimeria avium of birds and E. stiedÆ of rabbits closely resemble one another, but are not the same parasite, for E. avium is not infective to rabbits, nor E. stiedÆ to poultry.
Eimeria stiedÆ, Lindemann, 1865.
Syn.: Monocystis stiedÆ, Lindemann, 1865; Psorospermium cuniculi, Rivolta, 1878; Cytospermium hominis, Rivolta, 1878; Coccidium oviforme, Leuckart, 1879; Coccidium perforans, Leuckart, 1879; Coccidium cuniculi.
Fig. 70.—Eimeria stiedÆ. Section through an infected villus of rabbit’s intestine. ×260.
Eimeria stiedÆ is parasitic in the gut epithelium (fig.70), liver, and epithelium of the bile ducts of rabbits, and is usually considered to be the parasite very occasionally found in man. The life-cycle resembles that of Eimeria avium in its general outlines (see fig.69) and therefore will not be detailed in full here. The oÖcysts (fig.71) are large, elongate-oval, greenish in fresh preparations and vary in size from 24µ to 49µ long and 12·8µ to 28µ broad, the gut forms being usually smaller than those occurring in the liver, owing to the
Fig. 71.—Eimeria stiedÆ, from the liver of the rabbit, oÖcysts in various stages of development. (After Leuckart.)
Fig. 72.—a, b, spores of Eimeria stiedÆ (Riv.), with two sporozoites and residual bodies; c represents a free sporozoite. (After Balbiani.)
Fig. 73.—So-called swarm cysts (endogenous sporulation or schizogony) of the Coccidium of the rabbit. The daughter forms are called merozoites. (After R. Pfeiffer.)
The oÖcysts176 are thick-walled, somewhat flattened at one pole, where a large micropyle is present. Four egg-shaped spores (sporocysts) are formed within, each about 12µ to 15µ long and 7µ broad (fig.72). The oÖcysts are voided with the fÆces. Sporogony takes, in nature, about three days in the excrement. FÆcal contamination of the food of rabbits results, and coccidian oÖcysts are swallowed. Under the influence of the pancreatic juice of a new host, the sporozoites (fig.72, a—c) are liberated from the spores and proceed to attack the epithelium and multiply within it, as in the case of Eimeria avium. From the gut, infection spreads to the liver, where multiplication of the parasite goes on actively, resulting in the formation of the whitish coccidial nodules, which may be very conspicuous (fig.74). Proliferation of the connective tissue may occur around the coccidial nodules, which then contain large numbers of oÖcysts in various stages of development. It is said that the oÖcysts in the older nodules do not seem to be capable of further development. Schizogony (fig.73) and gametogony in all stages can be found in both liver and gut.
Young rabbits often die of intestinal coccidiosis before infection of the liver occurs. The repeated schizogony of Eimeria stiedÆ in the gut is sufficient to cause death.
Fig. 74.—Eimeria stiedÆ. Section through coccidian nodule in infected rabbit’s liver. ×55.
The disease of cattle popularly known as “red dysentery” is also ascribed to the action of Eimeria stiedÆ. The fÆces of infected cattle show blood clots of various sizes and in severe cases watery diarrhoea is present. Acute cases end fatally in about two days. Numerous oÖcysts, considered to be those of Eimeria stiedÆ, occur in the fÆces, and there is a heavy infection of the gut, especially the large intestine and rectum, all stages of the parasite being found in the epithelium. It is suspected that cattle contract the disease by feeding on fresh grass contaminated with oÖcysts. The disease is recorded from Switzerland and from East Africa.
As before mentioned, Eimeria stiedÆ is considered to be the organism found in a few cases in man, possibly acquired by eating the insufficiently cooked livers of diseased rabbits. These cases may now be described.
(a) Human Hepatic Coccidiosis.
(1) Gubler’s Case. A stone-breaker, aged 45, was admitted to a Paris hospital suffering from digestive disturbances and severe anÆmia. On examination the liver was found to be enlarged and presented a prominent swelling, which was regarded as being due to Echinococcus. At the autopsy of the man, who succumbed to intercurrent peritonitis, twenty cysts were found averaging 2 to 3cm. in diameter, and one measuring 12 to 15cm. The caseous contents consisted of detritus, pus corpuscles, and oval-shelled formations, which were considered to be Distoma eggs, but which, in accordance with Leuckart’s conjecture, proved to be Coccidia.177
(2) Dressler’s Case (Prague). Relates to three cysts, varying from the size of a hemp-seed to that of a pea, and containing Coccidia, found in a man’s liver.178
(3) Sattler’s Case (Vienna). Coccidia were in this case observed in the dilated biliary duct of a human liver.179
(4) Perls’ Case (Giessen). Perls discovered Coccidia in an old preparation of SÖmmering’s agglomerations.180
(5) Silcock’s Case (London).181 The patient, aged 50, who had fallen ill with serious symptoms, exhibited fever, enlarged liver and spleen, and had a dry, coated tongue. At the autopsy numerous caseous centres, mostly immediately beneath the surface, were found, while the contiguous parts of the liver were inflamed. Microscopical examination demonstrated numerous Coccidia in the hepatic cells as well as in the epithelium of the biliary ducts. A deposit of Coccidia was likewise found in the spleen, which the parasites had probably reached by means of the blood-stream.182
(b) Human Intestinal Coccidiosis.
In two cadavers at the Pathological Institute in Berlin, Eimer183 found the epithelium of the intestine permeated by Coccidia. Railliet and Lucet’s case may be traced back to intestinal Coccidia, which were found in the fÆces of a woman and her child, who had both suffered for some time from chronic diarrhoea.184 In other cases (Grassi, Rivolta), where only the existence of Coccidia in the fÆces was known, it is doubtful whether the parasites originated in the intestine or in the liver.
(c) Doubtful Cases.
To these belong Virchow’s case185 where, in the liver of an elderly woman, a thick walled tumour measuring 9 to 11mm. was found. Among the contents of this tumour there were oval formations 56µ long, surrounded by two membranes and enclosing a number of round substances. Virchow considered these foreign bodies to be eggs of pentastomes in various stages of development, others consider them to be Coccidia.
The Coccidia which Podwyssotzki claims to have seen in the liver of a man, not only in the liver cells, but also in the nuclei, are also problematic.186 The parasite was called Caryophagus hominis.
Again, other explanations can be given to an observation by Thomas, on the occurrence of Coccidium oviforme in a cerebral tumour of a woman aged 40. The growth was as large as a pea and surrounded by a bony substance.187
Genus. Isospora, AimÉ Schneider, 1881.
Syn.: Diplospora, LabbÉ, 1893.
Belonging to the section Disporea, that is, forming only two spores, each with four sporozoites.
Isospora bigemina, Stiles, 1891.
Syn.: “Cytospermium villorum intestinalium canis et felis,” Rivolta, 1874; “Coccidium Rivolta,” Grassi, 1882; Coccidium bigeminum, Stiles, 1891.
This parasite lives in the intestinal villi of dogs, cats, and the polecat (Mustela putorius, L.). According to Stiles,188 the oÖcyst divides into two equal ellipsoidal portions or sporoblasts which become spores and then each forms four sporozoites. The oÖcysts of this species vary from 22µ to 40µ in length and from 19µ to 28µ in breadth. Each spore is 10µ to 18µ long and contains four sporozoites. The parasites live and multiply, not only in the gut epithelium, but also in the connective tissue of the intestinal submucosa. Wasielewski has seen merozoites in the gut of the cat.
Isospora bigemina (fig.75) appears to occur also in man, for Virchow published a case which was communicated to him by Kjellberg, and attributed the illness to this parasite.189 Possibly also it would be more correct to ascribe the observation of Railliet and Lucet, which is mentioned under “Human Intestinal Coccidiosis,” p.148, to this species, as the Coccidia in that case were distinguished
Fig. 75.—Isospora bigemina, Stiles (from the intestine of a dog). a, Piece of an intestinal villus beset with Isospora, slightly enlarged; b, Isospora bigemina (15µ in diameter), shortly before division; c, divided; d, each portion encysted forming two spores; e, four sporozoites in each part, on the left seen in optical section, together with a residual body—highly magnified. (After Stiles.)
Doubtful Species.
In literature many other statements are found as to the occurrence of Coccidia-like organisms in different diseases of man. In some of the cases the parasites proved to be fungi. This was the case with the parasites of a severe skin disease of man, formerly called Coccidioides immitis and Coccidioides pyogenes. Other statements are founded on misapprehensions, or are still much disputed. If reference is here made to “Eimeria hominis,” R. Blanchard, 1895, this is done on the authority of the investigator mentioned. The structures in question are nucleated spindle-shaped bodies of very different lengths (18µ to 100µ), which either occurred isolated or were enclosed in large globular or oval cysts, alone or with a larger tuberculated body (“residual body”). These formations were found by J. KÜnstler and A. Pitres in the pleural exudation removed from a man by tapping. The man was employed on the ships plying between Bordeaux and the Senegal River.
Blanchard looks upon the fusiform bodies as merozoites and the cysts as schizonts of a Coccidium. On the other hand, Moniez declares the spindle bodies to be the ova and the supposed residual bodies to be “floating ovaries” of an Echinorhynchus.
Severi’s “monocystid Gregarines,” which were taken from the lung tissue of a still-born child, are also quite problematical.
No less doubtful are the bodies which Perroncito calls Coccidium jalinum, and which he found in severe diseases of the intestine in human beings, pigs, and guinea-pigs; Borini also reported another case.
Order. HÆmosporidia, Danilewsky emend. Schaudinn.
The HÆmosporidia are a group of blood parasites, comprising forms differing greatly among themselves. Some of the forms need much further investigation. However, there are certain true HÆmosporidia which present close affinities with the Coccidia, leading Doflein to use the term Coccidiomorpha for the two orders conjoined.
The HÆmosporidia present the following general characteristics:—
(1) They are parasites of either red or white blood corpuscles of vertebrates during one period of their life-history.
(2) They exhibit alternation of generations—asexual phases or schizogony alternating with sexual phases or sporogony—as do the Coccidia.
(3) There is also an alternation of hosts in those cases which have so far been completely investigated. The schizogony occurs in the blood or internal organs of some vertebrates while the sporogony occurs in an invertebrate, such as a blood-sucking arthropod or leech.
(4) Unlike the Coccidia, resistant spores in sporocysts are not generally produced, such protective phases in the life-cycle being unnecessary, as the HÆmosporidia are contained within either the vertebrate or invertebrate host during the whole of their life.
The HÆmosporidia may be considered for convenience under five main types:—
(1) The Plasmodium or HÆmamoeba type. This includes the malarial parasites of man and of birds. The asexual multiplicative or schizogonic phases occur inside red blood corpuscles and are amoeboid. They produce distinctive, darkish pigment termed melanin or hÆmozoin. Infected blood drawn and cooled on a slide may exhibit “exflagellation” of the male gametocytes, i.e., the formation of filamentous male gametes. The invertebrate host is a mosquito. The malarial parasites of man are discussed at length on p.155. Similar pigmented hÆmamoeboid parasites have been described in antelopes, dogs, and other mammals, and even reptiles.
(2) The Halteridium type. The trophozoite stage inside the red blood corpuscle is halter-shaped. Pigment is produced, especially near the ends of the organism. The parasites occur in the blood of birds. The invertebrate host of H. columbÆ of pigeons in Europe, Africa, Brazil and India, is a hippoboscid fly, belonging to the genus Lynchia.
Halteridium parasites are common in the blood of passerine birds, such as pigeons, finches, stone owls, Java sparrows, parrots, etc. The Halteridium embraces or grows around the nucleus of the host red cell without displacing the nucleus. Young forms and multiplicative stages of H. columbÆ have been found in leucocytes in the lungs of the pigeon (fig.76, 8-12). Male and female forms (gametocytes) are seen in the blood (fig.76, 3a, 3b). The cytoplasm of the
Fig. 76.—HÆmoproteus (Halteridium) columbÆ. Life-cycle diagram: 1, 2, stages in red blood corpuscle of bird; 3, 4, gametocytes (3a ?, 3b ?); 5a, formation of microgametes; 6, fertilization (in fly’s gut); 7, oÖkinete; 8–12, stages in mononuclear leucocytes in lungs. (After AragÃo.)
(3) The LeucocytozoÖn type. The trophozoites and gametocytes occur within mononuclear leucocytes and young red cells (erythro
Fig. 77.—LeucocytozoÖn lovati. a, Male parasite (microgametocyte), within host cell, whose ends are drawn out; b, female parasite (macrogametocyte) from blood of grouse. ×1,800. (After Fantham.)
The Leucocytozoa were first seen by Danilewsky in 1884. They are usually oval or spherical. It is not easy sometimes to distinguish the altered host cell from the parasite, as the nucleus of the former is pushed to one side by the leucocytozoÖn. The cytoplasm of the female parasite stains deeply, and the nucleus is rather small, containing a karyosome. In the male the cytoplasm stains lightly and the nucleus is larger, with a loose, granular structure.
Many species of Leucocytozoa are recorded, but schizogony has only been described by Fantham (1910)191 in L. lovati in the spleen of the grouse (Lagopus scoticus), and by Moldovan192 (1913) in L. ziemanni in the internal organs of screech-owls.
M. and A. Leger193 (1914) propose to classify Leucocytozoa, provisionally, according as the host cells are fusiform or rounded.
(4) The HÆmogregarina type. Included herein are many parasites of red blood corpuscles, with a few (the leucocytogregarines) parasitic in the white cells of certain mammals and a few birds. They are not amoeboid but gregarine-like, vermicular or sausage-shaped (fig.78). They do not produce pigment. They are widely distributed among the vertebrata, but are most numerous in cold-blooded vertebrates (fishes, amphibia and reptiles). The hÆmogregarines of aquatic hosts are transmitted by leeches, those of terrestrial hosts by arthropods.
The nucleus of hÆmogregarines is usually near the middle of the parasite, but may be situated nearer one end. The body of the parasite may be lodged in a capsule (“cytocyst”). There is much variation in size and appearance among hÆmogregarines. Some are small (Lankesterella); some attack the nucleus of the host cell (Karyolysus); others have full grown vermicules larger than the containing host corpuscle, and so the hÆmogregarines bend on themselves in the form of U (fig.78, b). Schizogony often occurs in the internal organs of the host, sometimes in the circulating blood.
The hÆmogregarines occurring in the white cells (mononuclears or polymorphonuclears) of mammals have been referred to a separate genus, Leucocytogregarina (Porter) or HepatozoÖn (Miller). Such leucocytogregarines are known in the dog (fig.79), rat, mouse, palm-squirrel, rabbit, cat, etc. Schizogony of these forms occurs in the internal organs, such as the liver, lung and bone-marrow of the hosts. They are apparently transmitted by ectoparasitic arthropods, such as ticks, mites, and lice.
Fig. 78.—HÆmogregarines from lizards, a, H. schaudinni, var. africana, from Lacerta ocellata; b, H. nobrei from Lacerta muralis; c, H. marceaui in cytocyst, from Lacerta muralis. (After FranÇa.)
A few hÆmogregarines are known to be parasitic in the red blood corpuscles of mammals. Such are H. gerbilli in the Indian field rat, Gerbillus indicus; H. balfouri (jaculi) in the jerboa, Jaculus jaculus, and a few species briefly described from marsupials. These parasites do not form pigment.
Strict leucocytic gregarines have been described from a few birds by AragÃo and by Todd.
The sporogony of hÆmogregarines is only known in a few cases, and in those affinity with the Coccidia is exhibited. In fact, the HÆmogregarines are now classified by some authors with the Coccidia.
(5) The Babesia or Piroplasma type. These are small parasites of red blood corpuscles of mammals. They do not produce pigment. They are pear-shaped, round or amoeboid in Babesia, bacilliform
Fig. 79.—Leucocytogregarina canis. Life-cycle diagram. Constructed from drawings by Christophers. (After Castellani and Chalmers.) Schizogony occurs in the bone-marrow. The parasite is transmitted from dog to dog by the tick, Rhipicephalus sanguineus, development in which, so far as known, is shown on the right.
THE MALARIAL PARASITES OF MAN.
Malaria, otherwise known as febris intermittens, chill-fever, ague, marsh fever, paludism, etc., is the name given to a disease of man, which begins with fever. It has been known since ancient times and is distributed over almost all the world, although very unevenly, but does not occur in waterless deserts and the Polar regions. In many places, especially in the civilized countries of Central Europe, the disease is extinct or occurs only sporadically, and large tracts of land have become free from malaria.
The rhythmical course of the fever is characteristic. It begins apparently suddenly with chilliness or typical shivering, whilst the temperature of the body rises, the pulse becomes low and tense and the number of beats of the pulse increases considerably. After half to two hours the heat stage begins. The patient himself feels the rise of his temperature (shown by feeling of heat, dry tongue, headache,
The intervals between the attacks are of varying length which permit of a distinction in the kinds of fever. If the attacks intermit one day, occurring on the first, third and fifth days of the illness and always at the same time of day, it is termed febris tertiana; if two days occur between fever days, it is called febris quartana. In the case of the fever recurring daily, later writers speak of typical febris quotidiana. But a quotidian fever may arise when two tertian fevers differing by about twenty-four hours exist at the same time (febris tertiana duplex). The patient has a daily attack, but the fever of the first, third and fifth days differs in some point (hour of occurrence, height of temperature, duration of cold or hot stage) from the fever of the second, fourth and sixth days. Similarly, two or three quartan fevers which differ by about twenty-four hours each may be observed together (febris quartana duplex or triplex); in the latter case the result is also a quotidian fever.
Two kinds of tertian fever are differentiated—a milder form occurring especially in the spring (spring tertian fever), and a more severe form appearing in the summer and autumn in warmer districts, especially in the tropics (summer or autumn fever, febris Æstivo-autumnalis, febris tropica, febris perniciosa). The latter often becomes a quotidian fever.
All the afore-mentioned infections are termed acute. They are distinguished from the very different chronic malarial infection by the frequent occurrence of relapses, which finally lead to changes of some organs and particularly of the blood. The relapses are then generally marked by an irregular course of fever.
The term masked malaria is used when any disturbance of the state of health of a periodic character shows itself and disappears after treatment with quinine.194 Generally it is a question of neuralgia.
That intermittent fever was an infectious disease, although not one which was transmitted direct from man to man, had been assumed for a long time. Therefore it was natural, at a time when bacteriology was triumphing, to look for a living agent causing infection in malaria, which search was, seemingly, successful (Klebs, Tomasi-Crudeli, 1879). Hence it was not surprising that the discovery of the
This supplied the starting point for further investigations, which were made not exclusively, but principally, by Italian investigators (Golgi, Marchiafava and Celli, Bignami and Bastianelli, Grassi and Feletti, Mannaberg, Romanowsky, Osier, Thayer and others). In 1885 Golgi described the asexual cycle in the blood, in the case of the quartan parasite. These investigations, after attention had been drawn by Danilewsky (1890) to the occurrence of similar endoglobular parasites in birds, were extended to the latter (Grassi and Feletti, Celli and Sanfelice, Kruse, LabbÉ and others).
The result was as follows: Malaria in man (and birds) is the result of peculiar parasites included in the Sporozoa by Metchnikoff, which parasites live in the erythrocytes, grow in size and finally “sporulate,” that is, separate into a number of “spores” which leave the erythrocytes and infect other blood corpuscles. Morphologically and biologically several species (and respectively several varieties) of malarial parasites may be distinguished, on which the different intermittent forms depend. Transmission of the blood of patients to healthy people produces a malarial affection which corresponds in character to the fever of the patient from whom the inoculation was made. The combined types of fever (tertiana duplex, quartana duplex or triplex) are explained by the fact that the patient harbours two or three groups of parasites which differ in their development by about twenty-four hours, whilst the irregular fevers depend on deviation from the typical course of development of the parasites. In addition to stages of the parasites which could easily be arranged in a developmental series concurrent with the course of the disease, other phases of the parasites also became known, such as spheres, crescents, polymitus forms, which seemed not to be included in the series and, therefore, were very differently interpreted.
The decision reached at the beginning of the last decade of the last century, which found expression in comprehensive statements (Mannaberg, Ziemann and others), only concerned a part of the complete development of the malarial parasites. No one could with any degree of certainty demonstrate how man became infected, nor were there reliable hypotheses based on analogy with other parasites concerning the exit of the excitants of malaria from the infected person and their further behaviour. Numerous hypotheses had been advanced, but none was able to elucidate the
In any case Ross (1898) had clearly established the importance of mosquitoes in the spread of malaria among birds. It was now only a question of proving whether, and how far, mosquitoes were concerned with human malaria. Ross himself worked to this end. Here the experiments of Italian investigators (Bignami, Bastianelli, Grassi)196 were of importance. These investigators studied the fate of malarial parasites in man, produced malaria in men experimentally by the bites of infected mosquitoes, and established that only mosquitoes belonging to the genus Anopheles were concerned, and not species of Culex. These latter are only able to transmit Proteosoma to birds. It is true that Culex can ingest the human malarial parasites, but the latter do not develop in them. Development only occurs in species of Anopheles. In Anopheles (and similarly for Proteosoma in Culex) sexual reproduction takes place; crescents, spheres and polymitus forms are necessary stages of development in the mosquito.
With these discoveries the campaign against malaria became more definite. It was directed partly against the transmitters, whose biology and life-cycle were more thoroughly investigated, instead of merely against the infection of the adult Anopheles. The latter do not, as was believed for some time, transmit the malarial germs to their offspring. They always infect themselves from human beings, whereby the relapses appearing in early summer, and the latent infection, especially of children of natives, play a principal part (Stephens and Christophers, Koch). Further, the crusade was directed against the infection of man by the bites of Anopheles. Important results have been obtained in these directions. Low and Sambon in 1900 lived in a mosquito-screened hut in a malarial part of the Roman Campagna for three of the most malarious months and did not contract the disease. In the same year Dr. P.T. Manson was infected with malaria by infected mosquitoes sent from Italy. The rÔle of mosquitoes having been proved, it may be hoped that ultimately the eradication of malaria, or at least a considerable restriction of it, will be achieved.
It is of importance to record that, although malarial parasites occur in mammals (monkeys, bats, etc.) the human ones are not transmissible to mammals, not even to monkeys. The species, therefore, are specific to the different hosts (Dionisi, Kossel, Ziemann, Vassall).
An important work dealing with the modern applications of the mosquito-malaria theory in all parts of the Tropics was published by Sir Ronald Ross in 1911. It is entitled “The Prevention of Malaria” (John Murray, London, 21s.).
DEVELOPMENT OF THE MALARIAL PARASITES OF MAN.
The commencement of the developmental cycle and of the infection of man, is the sporozoites (fig.80, 1) which are passed into the blood of a person by the bite of an infected mosquito. Prior to this the parasites collect in the excretory ducts of the salivary glands (fig.80, 27) of the Anopheles. The sporozoites are elongate and spindle-shaped, 10µ to 20µ long and 1µ to 2µ broad, with an oval nucleus situated in the middle. They are able to glide, perform peristaltic contractions, or curve laterally. Schaudinn has studied the penetration of the red blood corpuscles (fig.80, 2) by the sporozoites in the case of the living tertian parasite. The process takes forty to sixty minutes in drawn blood. After its entrance the parasite, which is now called a trophozoite, contracts, and becomes an active amoebula (fig.80, 3). It develops a food vacuole and grows at the expense of the invaded blood corpuscle (fig.80, 4), which is shown by the appearance of pigment granules (transformed hÆmoglobin) in it. When the maximum size is attained, multiplication by schizogony (fig.80, 5-7) begins with a division of the nucleus, which is followed by further divisions of the daughter nuclei, the number of which varies up to 16 or even 32, depending on the species of the parasite. Then the cytoplasm divides into as many portions as there are nuclei, the result being a structure suggestive of the spokes of a wheel or of a daisy, the centre of the resulting rosette being occupied by dark pigment. Finally, the parts separate from one another, leaving behind a residual body containing the pigment, and the daughter forms issue into the blood plasma as merozoites (fig.80, 7). They are actively amoeboid (fig.80, 8) and soon begin to enter other blood corpuscles of their host, for the entry into which thirty to sixty minutes are necessary, according to Schaudinn’s observations.197
Here they behave like sporozoites which previously entered and
Fig. 80.—Life-cycle of the tertian parasite (Plasmodium vivax). Figs.1 to 17, ×1,200; figs.18 to 27, ×600. (After LÜhe, based on figures by Schaudinn and Grassi.) 1, sporozoite; 2, entrance of the sporozoite into a red blood corpuscle; 3, 4, growth of the parasite, now sometimes called a trophozoite; 5, 6, nuclear division in schizont; 7, free merozoites; 8, the merozoites which have developed making their way into blood corpuscles, (arrow pointing to the left) and increase by schizogony (3–7); after some duration of disease the sexual individuals appear; 9a-12a, macrogametocytes; 9b-12b, microgametocytes, both still in the blood-vessels of man. If macrogametocytes (12a) do not get into the intestine of Anopheles they may perhaps increase parthenogenetically according to Schaudinn (12a; 13c-17c). The merozoites which have arisen (17c) become schizonts 3–7. The phases shown underneath the dotted line (13–17) proceed in the stomach of Anopheles. 13b and 14b, formation of microgametes; 13a and 14a, maturation of the macrogametes; 15b, microgamete; 16, fertilization; 17, oÖkinete; 18, oÖkinete in the walls of the stomach; 19, penetration of the epithelium of the stomach; 20–25, stages of sporogony on the outer surface of the intestinal wall; 26, migration of the sporozoites to the salivary gland; 27, salivary gland with sporozoites.
The growth and schizogony last different times, according to the species of the parasite, about forty-eight hours in the case of the parasite of febris tertiana or tropica, and seventy-two hours for the quartan parasite. The various intermittent forms produced by them depend on this specific difference in the malarial parasites.
The schizogony can, however, only be repeated a certain number of times, supposing that the disease has not been checked prematurely by the administration of quinine, which is able to kill the parasites. It appears that after a number of attacks of fever the conditions of existence in man are unfavourable for the malarial parasites, and this brings about the production of other forms which have long been known, but also long misunderstood (spheres, crescents, polymitus). The merozoites in this case no longer grow into schizonts, or at least not all of them, but become sexual individuals called gametocytes (fig.80, 9-12), which only start their further development when they have reached the intestine of Anopheles. This does not take place in every case, nor with all the gametocytes which exist in the blood of patients with intermittent fever. Of those parasites which remain in the human blood the male ones (microgametocytes) soon perish, the females (macrogametocytes) persist for some long time, and perhaps at last acquire the capacity of increasing by schizogony. They might thus form merozoites which behave in the body as if they had proceeded from ordinary schizonts (fig.80, 13c-17c). If their number increases sufficiently, in course of time the patient, who was apparently recovering, has a new series of fever attacks, or relapses, without there having been a new infection. This is the view of Schaudinn, who from researches of his own concluded that relapses were brought about by a sort of parthenogenetic reproduction of macrogametocytes. R. Ross, on the contrary, believes that in the
Fig. 81.—Stages of development of pernicious or malignant tertian parasites in the intestine of Anopheles macultpennis. (After Grassi.) a, macrogametocyte (crescent) still attached to human blood corpuscles; b, macrogametocyte (sphere) half an hour after ingestion by the mosquito; c, microgametocyte (crescent) attached to the blood corpuscle; d, microgametocyte (sphere) half an hour after ingestion; the nucleus has divided several times; e, microgametes attached to the residual body (polymitus stage).
Fig. 82.—OÖkinete of the malignant tertian parasite in the stomach of Anopheles maculipennis, thirty-two hours after ingestion of blood. (After Grassi.)
If the gametocytes, which are globular, or in the pernicious or malignant tertian parasite crescentic (fig.81), gain access to the intestine of an Anopheline,199 they mature. The macrogametocytes extrude a part of their nuclear substance (fig.80, 13a, 14a) and thereby become females or macrogametes. The microgametocytes, on the other hand, undergo repeated nuclear division, preparation for this being made apparently whilst in the blood of man. This results in the formation of threadlike bodies which move like flagella and finally detach themselves from the residual body (fig.80, 13b, 14b). These are the males or microgametes200 (fig.80, 15b).
Fig. 83.—Section of the stomach of an Anopheles, with cysts (oÖcysts) of the malignant tertian parasite. (After Grassi).
Copulation takes place in the stomach of the Anopheline (fig.80, 16). A microgamete penetrates a macrogamete and coalesces with it. The
The sporulation (figs.80, 21-25; 84), which now follows, begins with repeated multiple fission of the nucleus. Long before the definitive number of nuclei, which varies with the individual, is attained the protoplasm, according to Grassi, begins to segment around the individual large nuclei but without separating completely into cell areas. According to Schaudinn, however, there is a condensation of the outstanding protoplasmic strands. It is certain that the number of nuclei increases with simultaneous decrease in size. They soon appear on the surface of the strands or sporoblasts, surround themselves with some cytoplasm and then elongate (fig.84). In this manner the sporozoites are formed and break away from the unused remains of the cytoplasmic strands of the sporoblasts (fig.80, 26). The number of the sporozoites in an oÖcyst varies from several hundreds to ten thousand.
Fig. 84.—Four different sporulation stages of malarial parasites from Anopheles maculipennis, much magnified. a-c, of the malignant tertian parasite; a, four to four and a half days after sucking; b and c, five to six days after sucking; d, of the tertian parasite, eight days after sucking. (After Grassi.)
The sporulation is influenced in its duration by the external temperature (Grassi, Jansci, Schoo). In the tertian parasite it takes place quickest at a temperature of 25° to 30°C. and takes eight to nine days. A temperature a few degrees lower has a retarding effect (eighteen to nineteen days at 18° to 20°C). A still lower one has a restraining or even destructive effect. Temperatures over 35°C. also exercise a harmful effect. The malignant tertian parasite seems to need a somewhat higher temperature and the quartan parasite a lower one.
The sporozoites of the various malarial parasites show no specific differences. They were stated by Schaudinn to occur in three forms, and these were described as indifferent (neuter), female and male. There is, however, little or no evidence for this hypothetical differentiation. The last were said to perish prematurely, that is, in the oÖcyst. The others after the rupture of the oÖcysts enter the body cavity of the Anophelines, whence they are carried along in the course of the blood. Finally they penetrate the salivary glands (fig.80, 27) probably by their own activity, break through their epithelia and accumulate in the salivary duct (fig.80, 27). At the next bite by the mosquito they are transmitted to the blood-vessels of man.
The Species of Malarial Parasites of Man.
In view of the differences in opinion regarding “species” and “varieties,” the dispute whether the malarial parasites of man represent one species with several varieties, or several species is almost superfluous. If necessary two genera may be distinguished.
The parasites of the tertian and quartan fever are alike in that their gametocytes have a rounded shape (figs.80, 12, 13), whilst the corresponding stages of the pernicious or malignant tertian parasites are crescentic (figs.81, 88). These differences are used by some writers as the distinguishing characteristic of two genera: Plasmodium, Marchiafava and Celli, 1885, for the first mentioned species; Laverania, Grassi and Feletti, 1889, for the pernicious or malignant tertian parasite. Whether there is a genuine quotidian fever and accordingly a special quotidian parasite is still disputed.
These parasites are treated in practical detail in Stephens and Christophers’ “Practical Study of Malaria,” 3rd edition, 1908.
Plasmodium vivax, Grassi and Feletti, 1890.
Syn.: HÆmamoeba vivax, Grassi and Feletti, 1890; Plasmodium malariÆ var. tertianÆ, Celli and Sanfelice, 1891; HÆmamoeba laverani var. tertiana, LabbÉ, 1894; HÆmosporidium tertianum, Lewkowitz, 1897; Plasmodium malariÆ tertianum, LabbÉ, 1899: HÆmamoeba malariÆ var. magna, Laveran, 1900, p.p.; HÆmamoeba malariÆ var. tertianÆ, Laveran, 1901.
This species, P. vivax,201 is the causal agent of the simple or spring tertian fever and is, therefore, named directly the tertian or benign tertian parasite (figs.80, 3-8; 85). During the afebrile period in the patient, the young trophozoites or amoebulÆ appear on or in the red blood corpuscles as pale bodies of 1·5µ to 2µ diameter which at first show only slow amoeboid movements. Their nucleus is difficult to recognize in the early stage. Soon the food vacuole is formed and this grows concomitantly with the trophozoite and the parasite has a ring-like appearance. Afterwards the vacuole diminishes, and at this
Fig. 85.—Development of the tertian parasite in the red blood corpuscles of man; on the right a “Polymitus.” (After Mannaberg.) See also fig.80, 3—7.
Around each nucleus a portion of cytoplasm collects and thus young merozoites are produced. These separate from each other and from the little residual masses202 which contain the melanin and pass from the blood corpuscles, which now can hardly be recognized, to the blood plasma, where they soon attack new erythrocytes.
The migration of the merozoites initiates a new attack of fever and two groups of tertian parasites in the blood, differing in development by about twenty-four hours, are the conditions for febris tertiana duplex.
After a lengthy duration of fever the gametocytes (figs.80, 9—12) appear. They are uninucleate. The microgametocytes are about the size of fully developed schizonts, the macrogametocytes are somewhat larger. Their further development takes place in Anophelines.
The chief distinctive characteristics of the simple tertian parasite, as seen in infected blood, are:—(1) The infected red-cell is usually enlarged; (2) the presence of fine red granules known as SchÜffner’s dots in the red blood corpuscles, after Romanowsky staining; (3) the fragile appearance of the parasite compared with other species. Large forms are pigmented, irregular and “flimsy-looking,” sometimes appearing to consist of separate parts. Irregularity of contour is common.
Ahmed Emin203 (1914) has described a small variety of P. vivax.
Plasmodium malariÆ, Laveran.
Syn.: Oscillaria malariÆ, Laveran, p.p., 1883; HÆmamoeba malariÆ, Gr. et Fel., 1890; Plasmodium malariÆ var. quartanÆ, Celli et Sanfel., 1891; HÆmamoeba laverani var. quartana, LabbÉ, 1894; HÆmosporidium quartanÆ, Lewkowitz, 1897; Plasmodium malariÆ quartanum, LabbÉ, 1899; Plasmodium golgii, Sambon, 1902; Laverania malariÆ, Jancso, 1905 nec Grassi et Fel. 1890; HÆmomoeba malariÆ var. quartanÆ; Lav., 1901.
Plasmodium malariÆ is the parasite of quartan malaria (fig.86). The trophozoites of the quartan parasite differ from the corresponding stages of the tertian parasite in that their motility is less and soon ceases. They differ also in their slower growth, by the early disappearance of the food vacuole, by the more marked formation of the dark brown pigment, and by the fact that the red blood corpuscles attacked are not altered either in colour or size.
Fig. 86.—Development of the quartan parasite in the red corpuscles of man—asexual stages. (After Manson.)
When the parasites have grown almost to the size of the erythrocytes schizogony occurs. The pigment granules arrange themselves in lines radiating towards the centre and the merozoites are also radially disposed in groups of 6, 8, 10 or even 12, but are often arranged less regularly. The whole development, growth and schizogony, occupies seventy-two hours.
The appearance of quartana duplex or triplex is conditional on the presence in the blood of the patient of two or three groups of Plasmodia differing in their development by twenty-four hours.
The chief distinctive characters of the quartan parasite are: (1) The erythrocyte is unchanged in size; (2) the rings are compact and show pigment early; in the larger forms the chromatin is dense and relatively plentiful; (3) the pigment, which is relatively well-marked, may be arranged at the periphery.
Laverania malariÆ, Grassi and Feletti, 1890 = Plasmodium falciparum, Welch, 1897.
Syn.: Plasmodium malariÆ var. quotidianÆ, Celli et Sanf., 1891; HÆmamoeba malariÆ prÆcox, Gr. et Fel., 1892 (nec H. prÆcox, Gr. et Fel., 1890); HÆmamoeba laverani, LabbÉ, 1894; HÆmatozoÖn falciparum, Welch, 1897; HÆmosporidium undecimanÆ and H. sedecimanÆ and H. vigesimo-tertianÆ, Lewkowitz, 1897; HÆmamoeba malariÆ parva, Lav., 1900; Plasmodium prÆcox, Dofl., 1901; Plasmodium immaculatum, Schaud., 1902; Plasmodium falciparum, Blanch., 1905.
The names most commonly used for the parasite of malignant tertian malaria are Plasmodium falciparum and Laverania malariÆ.
The summer and autumn fever (febris Æstivo-autumnalis), also called malignant tertian or sub-tertian, is caused by a malarial parasite which is distinguished by the small size of its schizont, while the gametocytes are crescentic (figs.81, 88).
Most authors identify this kind of fever or the parasites which cause it (Laverania malariÆ) with the pernicious malaria of the tropics. Ziemann, however, repeatedly has drawn attention to certain small but definite differences between the usual malignant tertian or pernicious parasites which occur in the tropics and the tropical parasites of some malarial districts, particularly of West Africa, and insists that at least two varieties or sub-species occur. Other investigators distinguish from this or these forms a quotidian parasite. On the other hand, the assertion is made that there are no specific differences, but that the malignant or pernicious tertian parasite which normally needs forty-eight hours for its development in the blood of man, can also develop in twenty-four hours. The establishment of the duration of the development is a matter of especial difficulty, because the stages of schizogony are far less numerous in the peripheral blood than in that of the internal organs. It is also stated that the tropical parasite very seldom forms crescentic but rather rounded gametocytes. According to such an observation the organism would belong to Plasmodium and not to Laverania. The question whether the tropical fevers are caused by two different parasites does not seem to be definitely settled.
The young trophozoite of the malignant, pernicious tertian, or sub-tertian parasite (fig.87) are but slightly active and are very small, even after the formation of the comparatively large food vacuole, which makes the body appear annular (“signet ring” stage). Often two and even more parasites are found in one blood corpuscle.
Fig. 87.—The pernicious malignant or sub-tertian parasite in the red corpuscles of man, asexual stages. (After Manson.)
Fully grown they only attain two-thirds or less of the diameter of the erythrocytes, which display an inclination to shrink and then appear
About thirty hours after the entrance into the blood corpuscles, the parasites are rarely found in the peripheral blood, but they are present in the internal organs, and especially in the spleen. The schizogony, which now begins in the internal organs, proceeds on the same lines as that of the quartan parasite, that is, usually with the merozoites radially arranged around a central agglomeration of dark brown pigment.
The number of merozoites formed is quoted differently, e.g., 8 to 24, on an average 12 to 16. However, according to the recent cultural researches of J.G. and D. Thomson204 (1913) the number of merozoites of P. falciparum is 32. D. Thomson, from examination of spleen smears at autopsy, also concludes that the number of merozoites may reach 32. During their formation the blood corpuscle which is attacked gets paler and disintegrates.
Fig. 88.—The crescents of the malignant tertian parasite. (After Mannaberg.) See also fig.81.
The gametocytes which finally appear are attenuated, curved bodies, rounded at each end and known as crescents (figs.81, 88), and are provided with a nucleus and with coarse pigment masses. In the males the pigment is more scattered than in the females, where it is around the nucleus. Their length is 9µ to 14µ, and their breadth is
D. Thomson (1914),205 from studies of autopsy smears, has shown that crescents develop chiefly in the bone-marrow and spleen, and take about ten days to grow into the adult state in the internal organs. He believes that crescents are produced from ordinary asexual spores. Quinine, he states, has no direct destructive action on crescents, but it destroys the asexual source of supply.
The sporozoites of Laverania malariÆ (P. falciparum) are represented in fig.89.
Fig. 89.—Section through a tubule of the salivary gland of an Anopheles with sporozoites of the malignant tertian parasites; on the left at the top a single sporozoite greatly magnified. (After Grassi).
The principal distinctive characters of the malignant tertian parasite are: (1) The ring forms are very small, occasionally bacilliform, and may be marginal (“accolÉ” of Laveran); (2) the larger trophozoites are often ovoid, and about one-third or one-half of the erythrocyte in size; (3) the infected red cells sometimes show coarse
J.W.W. Stephens (1914) has described a new malarial parasite of man; it is called Plasmodium tenue. It is very amoeboid, with scanty cytoplasm and much chromatin, sometimes rod-like or irregular. The parasite was described from a blood-smear of an Indian child. The creation of a new species for this parasite has been criticized by Balfour and Wenyon, and by Craig.
Plasmodium relictum, Sergent, 1907.
Syn.: Plasmodium prÆcox, Grassi and Feletti, 1890; Plasmodium danilewskyi, Gr. et Fel., 1890; HÆmamoeba relicta, Gr. et Fel., 1891; Proteosoma grassii, LabbÉ, 1894.
HÆmamoeboid, pigment-producing, malarial parasites are often found in birds. Like the human malarial parasites they have been variously named. LabbÉ created the genus Proteosoma for them, and this name is still often used as a distinctive one unofficially. The correct name is stated to be either Plasmodium relictum or P. prÆcox, or possibly even P. danilewskyi, assuming that there is only one species. The nomenclature of the malarial parasites is most confused. The avian malarial parasites are transmitted by Culicine mosquitoes.
The organism was discovered by Grassi in the blood of birds in Italy, and causes a fatal disease in partridges in Hungary. Sparrows are affected in India, and it was this Plasmodium in which Ross first traced the development of a malarial parasite in a mosquito. The parasite may be transmitted from bird to bird by blood-inoculation, canaries being very susceptible.
The principal stages of the avian plasmodium closely resemble those of the malarial parasites of man. In its earliest stage P. relictum is unpigmented, but soon the trophozoite grows and becomes pigmented, meanwhile displacing the nucleus of the avian red-blood corpuscle, a characteristic feature, distinguishing it from Halteridium. Schizonts are formed, each of which gives rise to about nine merozoites in the circulating blood. Sexual forms or gametocytes also occur in the blood. These develop in Culex fatigans, C. pipiens and C. nemorosus. OÖkinetes or vermicules are formed in twelve to fifteen hours in the stomach of the mosquito, and in one to two days well-developed round oÖcysts may be seen. In three to four days sporoblasts have formed within the oÖcysts and young sporozoites begin to develop. In nine to ten days the oÖcysts are mature, being filled with sporozoites. The oÖcysts then burst and the sporozoites travel through the thoracic muscles to the salivary glands of the Culicine.
Neumann, experimenting with canaries, found that Stegomyia fasciata could transmit the infection, but less efficiently than species of Culex.
The Cultivation of Malarial Parasites.
The successful cultivation of malarial parasites in vitro was first recorded by C.C. Bass and by Bass and Johns (1912).206 Since then, J.G. and D. Thomson,207 and McLellan (1912–13), Ziemann208 and others have repeated the experiments.
DIFFERENTIAL CHARACTERS OF THE HUMAN MALARIAL PARASITES.
| Character | Plasmodium malariÆ (Quartan) | Plasmodium vivax (Benign tertian) | Laverania malariÆ = Plasmodium falciparum (Malignant tertian) |
|---|---|---|---|
| Schizogony | Complete in seventy-two hours | Complete in forty-eight hours | Complete in forty-eight hours or less |
| Trophozoite | Smaller than P. vivax, larger than L. malariÆ | Young trophozoite large. | Young trophozoite small |
| Pseudopodia not marked or long | Long pseudopodia | ||
| Movements | Rather slow in immature forms | Active amoeboid movements | Sometimes actively motile |
| Pigment | Coarse granules, peripherally arranged, little movement | Fine granules, with active movement | Granules fine and scanty, movement oscillatory |
| Schizont | Smaller than red corpuscle | Larger than red blood corpuscle | Smaller than red corpuscle |
| Merozoites | 6 to 12 forming rosette | 15 to 20 regularly arranged | 8 to 32 (according to different authors) arranged irregularly |
| Gametocytes | Spherical | Spherical | Crescentic |
| Distribution of parasites in vertebrate host | About equal number in peripheral and visceral blood | Larger numbers in visceral blood | Scanty in peripheral blood compared with the enormous numbers in the internal organs. The latter part of the cycle (schizogony) may occur in the internal organs only |
| Alterations in erythrocytes | Almost normal | Pale and hypertrophied. | Corpuscle may be shrunken and dark, or may be colourless. Maurer’s coarse dots sometimes seen |
| SchÜffner’s dots seen in deeply stained specimens |
Essentially the method of cultivation, as used by Thomson, is as follows: 10c.c. of infected blood are drawn from a vein and transferred to a sterile test tube, in which is a thick wire leading to the bottom of the tube. One-tenth of a cubic centimetre of a 50 per cent. aqueous solution of glucose or dextrose is placed in the test tube, preferably before adding the blood. The blood is defibrinated by stirring gently with the wire. When defibrination is complete the wire and the clot are removed, and the glucose-blood is transferred, in portions, to several smaller sterile tubes, each containing a column of blood about one inch in height. The tubes are plugged and capped and then transferred, standing upright, to an
So far only the asexual generation of the malarial parasites has been grown in vitro. Thomson rarely observed hÆmolysis in the cultures. Clumping of the malignant tertian parasites occurred. In cultures of the benign tertian parasite (Plasmodium vivax) clumping was not observed. J.G. and D. Thomson consider that this difference as regards clumping explains why only young forms of malignant tertian are found in peripheral blood, as the clumping tendency of the larger forms causes them to be arrested in the finer capillaries of the internal organs. It also explains the tendency to pernicious symptoms, such as coma, in malignant tertian malaria. Further it was found from cultures that P. falciparum was capable of producing thirty-two spores (merozoites) in maximum segmentation, while P. vivax produced sixteen spores (merozoites) as a rule, though the number might be greater than sixteen. (Quartan parasites produce eight spores or merozoites in schizogony.)
It may also be mentioned here that Babesia (Piroplasma) canis has been successfully cultivated in vitro by Bass’s method. This has been accomplished by Thomson and Fantham,209 Ziemann, and Toyoda in 1913. J.G. Thomson and Fantham used the simplified Bass technique recorded above, namely, infected blood and glucose, incubating at 37°C. In one of the B. canis cultures, starting with heart blood of a dog containing corpuscles infected with one, two, or, exceptionally, four piroplasmata, Thomson and Fantham succeeded in obtaining a maximum of thirty-two merozoites in a corpuscle. The cultures are infective to dogs and sub-cultures have been obtained.
Family. PiroplasmidÆ, FranÇa.
The parasites included in this provisional family or group belong to the HÆmosporidia. They are minute organisms, sometimes amoeboid, but usually possessing a definite form. They are endoglobular, being contained within mammalian red blood corpuscles, but they produce no pigment. The true Piroplasmata, belonging to the genus Babesia, destroy the host corpuscles, setting free the
Fig. 90.—Nuttallia equi, life-cycle as seen in red blood corpuscles in stained preparations of peripheral blood. (After Nuttall and Strickland.)
Of recent years, researches on the morphology of these blood parasites has led to their separation into various genera and species. However, our knowledge is still very far from complete. The various
(1) Babesia (Starcovici) or Piroplasma (Patton). Pyriform parasites, dividing by a special form of budding or gemmation with chromatin forking, as well as by direct binary fission. Parasitic in oxen, dogs, sheep, horses, etc.
(2) Theileria (Bettencourt, FranÇa and Borges). Rod-shaped and oval parasites occurring in cattle and deer. T. parva is the pathogenic agent of African East Coast fever in cattle.
(3) Nuttallia (FranÇa). Oval or pear-shaped parasites, with multiplication in the form of a cross. N. equi211 (fig.90) of equine “piroplasmosis” (nuttalliosis). N. herpestidis in a mongoose.
(4) Nicollia (Nuttall). Oval or pear-shaped parasites with characteristic nuclear dimorphism, and with quadruple division at first fan-like, then like a four-leaved clover. N. quadrigemina from the gondi.
(5) Smithia (FranÇa). Pear-shaped, single forms stretching across the blood corpuscle. Multiplication into four in the form of a cross. S. microti from Microtus arvalis, S. talpÆ from the mole.
(6) Rossiella (Nuttall). This belongs to the family PiroplasmidÆ of FranÇa. It is intracorpuscular and non-pigment forming, occurring singly, in pairs, or occasionally in fours. It is usually round and larger than Babesia. The parasite multiplies by binary fission. R. rossi in the jackal.
The genus Babesia is the best known and most important, and will be considered next.
Genus. Babesia, Starcovici, 1893.
Syn.: Pyrosoma, Smith and Kilborne, 1893; Apiosoma, Wandolleck, 1895; Piroplasma, W.H. Patton, 1895; Amoebosporidium, Bonome, 1895.
The organisms belonging to this genus are pyriform, round or amoeboid. The characteristic mode of division is as follows: Just before division the parasite becomes amoeboid and irregular in shape, (fig.91, 1–5) with a compact nucleus. The latter gives off a nuclear bud. This nuclear bud divides into two by forking (fig.91, 6, 7). The chromatin forks grow towards the surface of the body of the rounded parasite, and then two cytoplasmic buds grow out. The forking nuclear buds, which are Y-shaped, pass into the cytoplasmic outgrowths212 (fig.91, 8, 9). The buds gradually increase in size at
Fig. 91.—Babesia (Piroplasma) canis, life-cycle in stained preparations of infected blood of dog. (After Nuttall and Graham-Smith.)
The distribution of the chromatin in the pear-shaped Babesia, as seen in B. canis and B. bovis, is interesting. The main nuclear body consists of a karyosome surrounded by a clear area. There is also a loose (chromidial) mass of chromatin representing the remains of the chromatin forks seen during the formation of the parasite as a daughter form by gemmation. Occasionally there is a small dot or point, the so-called “blepharoplast” of Schaudinn and LÜhe. This minute dot is not a flagellate blepharoplast, for there is no flagellate stage in the life-history of Babesia. These nuclear phenomena have been described by Nuttall and Graham-Smith and Christophers (1907)214 for B. canis, by Fantham (1907)215 for B. bovis, and by Thomson and Fantham (1913) from glucose-blood cultures of B. canis.
Babesia are tick borne, as was first shown by Smith and Kilborne (1893). The developmental cycle in the tick is incompletely known. The best accounts are those of Christophers (1907)216 for B. canis and Koch (1906) for B. bovis, and these accounts are supplementary. The principal stages, so far as known, may be summarized thus:—
(1) The piroplasms taken by the tick in feeding on blood pass into the tick’s stomach. The pyriform parasites, which alone are capable of further development, are set free from the blood corpuscles. In about twelve to eighteen hours they become amoeboid, sending out long, stiff, slender, pointed pseudopodia. The nucleus of each parasite divides unequally into two. Similar forms have been obtained in cultures. These stellate forms may be gametes, and according to Koch fuse in pairs.
(2) A spherical stage follows, possibly representing the zygote. This grows, and a uninucleate globular mass results. This form is found in large numbers on the third day, according to the observations of Koch.
(3) A club-shaped organism is next formed. This may represent an oÖkinete stage. The club-shaped bodies are motile and gregarine-like, and are about four times the size of the blood forms. These club-shaped bodies and subsequent stages were described by Christophers in the development of B. canis in the dog-tick, Rhipicephalus sanguineus.
(4) The club-shaped bodies pass from the gut of the tick into the ovary, and so get into the ova. There they become globular, and later are found in the cells of the developing tick-embryo. The parasites are, then, transmitted hereditarily. Similar globular bodies are found in the tissue cells of the body of tick nymphs which have taken up piroplasms. The globular stage was called the “zygote” by Christophers, but it may correspond to the oÖcyst of Plasmodia.
(5) The globular body divides into a number of “sporoblasts,” which become scattered through the tissues of the larval or nymphal tick, as the case may be.
(6) The sporoblasts themselves divide into a large number of sporozoites, which are small uninucleate bodies, somewhat resembling blood piroplasms. The sporozoites collect in the salivary glands of the tick. They are inoculated into the vertebrate when the tick next feeds.
The chief species of Babesia and their pathogenic importance may be listed thus:—
(1) Babesia bovis (Babes) produces infectious hÆmoglobinuria of cattle in Europe and North Africa. It is transmitted by Ixodes ricinus. A similar parasite also occurs in deer.
(2) Babesia bigemina (Smith and Kilborne) produces Texas fever, tristeza, or red-water in cattle in North and South America, South Africa and Australia. It is transmitted by BoÖphilus annulatus in North America, by B. australis in Australia, South America, and the Philippines, and by B. decoloratus in South Africa.
The parasite is from 2µ to 4µ long, and from 1·5µ to 2µ broad.
Babesia bigemina may be the same parasite as B. bovis.
(3) Babesia divergens (MacFadyean and Stockman) is a small parasite. It is found in cattle suffering from red-water in Norway, Germany, Russia, Hungary, Ireland, Finland, and France, and is transmitted by Ixodes ricinus.
(4) Babesia canis (Piana and Galli-Valerio) gives rise to malignant jaundice or infectious icterus in dogs in Southern Europe, India, and other parts of Asia and North Africa, where it is transmitted by Rhipicephalus sanguineus. In Africa generally, especially South Africa, the disease is transmitted by HÆmaphysalis leachi. Babesia canis varies from 0·7µ to 5µ, the size depending partly on the number of parasites within the corpuscle. It averages about 3µ. It has been cultivated in Bass’ medium (glucose and infected blood), see p.172.
In India Piroplasma gibsoni (Patton) infects hunt dogs and jackals. It is annular or oval in shape.
(5) Babesia ovis (Babes) produces “Carceag,” a disease of sheep in Roumania, the Balkan Peninsula, Italy, and Transcaucasia. It varies in size from 1µ to 3µ. It is transmitted by Rhipicephalus bursa. The parasite has recently been recorded from Rhodesia.
(6) Babesia caballi (Nuttall and Strickland) causes “biliary fever” in equines. The parasite occurs in Russia, Roumania, and
It should be mentioned that Nuttallia equi also causes “piroplasmosis” in equines, with symptoms of hÆmoglobinuria and jaundice in Italy, Sardinia, many parts of Africa, Transcaucasia, India, and Brazil. In Africa it is transmitted by Rhipicephalus evertsi. It has been shown experimentally that a horse recovered from Babesia caballi was susceptible to the inoculation of Nuttallia equi blood.
(7) Babesia pitheci (P.H. Ross) was found in a monkey, Cercopithecus sp., in Uganda. The pear-shaped forms measure 1·5µ by 2·5µ.
(8) Babesia muris (Fantham)217 was found in white rats. The pyriform parasites are 2µ to 3µ long and 1µ to 1·5µ broad; oval forms are 0·5 to 1·5µ diameter.
The usual symptoms of babesiasis (piroplasmosis) are high fever, loss of appetite, hÆmoglobinuria, icterus, anÆmia, paralysis, and death in about a week in acute cases. In chronic cases there is anÆmia, and hÆmoglobinuria is less marked. When animals recover, there are still some piroplasms left in the blood. “Recovered” or “salted” animals are not susceptible to reinfection, but ticks feeding on them acquire piroplasms, and are a source of danger to freshly imported animals.
Treatment.—Trypan-blue is the best drug, as shown by Nuttall and Hadwen218 (1909). It should be administered intravenously in 1 to 1·5 per cent. aqueous solution. A dose of 5 to 10c.c. is curative for dogs, one of 100 to 150c.c. for horses and cattle. Unfortunately, the tissues are coloured blue by the drug. The “salted” animals, after trypan-blue treatment, still harbour the parasites in their blood for years.
Genus. Theileria, Bettencourt, FranÇa and Borges, 1907.
The organisms belonging to this genus are rod-like or bacilliform, and coccoid or round.
The best known of the species of Theileria is T. parva, the pathogenic agent of East Coast fever or Rhodesian fever in cattle in Africa.
Theileria parva, Theiler, 1903.
Syn.: Piroplasma parvum.
In the blood corpuscles of infected cattle minute rod-like and oval parasites are seen. Some are comma shaped and others are clubbed (fig.92, 1–12). The rod-like forms measure 1µ to 3µ in length by 0·5µ in breadth; the oval forms are 0·7µ to 1·5µ in diameter. The intracorpuscular parasites are said by R. Gonder (1910) to be gametocytes, the rod-like forms being thought to be males, the oval forms to be females. Free parasites are practically never seen in the blood. It is known that it is impossible to
Fig. 92.—Theileria parva. 1–12, intracorpuscular parasites, stained. (After Nuttall and Fantham); 13–18, Koch’s blue bodies, from stained spleen smear; 17–18, breaking up of Koch’s body. (After Nuttall.)
In the internal organs, especially the lymphatic glands, spleen and bone-marrow, are found multinucleate bodies known as Koch’s blue bodies (fig.92, 13–18). These are schizonts, according to Gonder.220 The actual Koch’s blue bodies are said to be extracellular, but similar multinucleate bodies, schizonts, occur in lymphocytes. The schizonts divide and the merozoites resulting probably invade the red blood corpuscles in the internal organs. Gonder considers that the sporozoites injected by the tick collect in the spleen and lymphatic glands, penetrate the lymphocytes and give rise to the schizonts.
Gonder has studied the cycle of T. parva in the tick. He states that the gametocytes leave the host corpuscles and give rise to gametes, then conjugation occurs producing zygotes. The zygotes are then said to become active to form ookinetes, and to enter the salivary glands of the tick. Multiplication is said to occur therein, producing a swarm of sporozoites. This work needs confirmation.
T. parva is transmitted by Rhipicephalus appendiculatus, R. simus, R. evertsi, R. nitens, and R. capensis. The parasites are not hereditarily transmitted in Rhipicephalus, but when taken by the transmitter at one stage of its development the tick is infective in its next stage (e.g., if the larva becomes infected, then the nymph is infective; if the nymph becomes infected, then the adult is infective).
An animal recovered from Theileria parva is incapable of infecting ticks, but few animals recover from East Coast fever. Animals suffering therefrom do not show hÆmoglobinuria.
Theileria mutans, Theiler, 1907·
Syn.: Piroplasma mutans.
This is transmissible experimentally by blood inoculation. It occurs in cattle in South Africa and Madagascar and is apparently non-pathogenic. No Koch’s blue bodies are formed. It is transmitted by ticks.
Theileria annulata (Dschunkowsky and Luhs) occurs in cattle in Transcaucasia.
A Theileria (T. stordii) has been found in a gazelle (FranÇa, 1912).
Genus. Anaplasma, Theiler, 1910.
This genus221 may be mentioned here. The organisms included therein are, according to Theiler, coccus-like, consisting of chromatin, and are devoid of cytoplasm. They occur in the red blood corpuscles of cattle, causing a disease characterized by destruction of red cells, fever and anÆmia, but with yellow urine. The disease is tick transmitted. The bodies now called Anaplasma marginale were formerly described as marginal points. They multiply by simple fission. They are said by Theiler to cause gall-sickness in cattle in South Africa. Some authors doubt whether these bodies are organismal.
Genus. Paraplasma, Seidelin, 1911.
Under this generic name Seidelin described certain bodies found by him in cases of yellow fever in 1909. The type species is P. flavigenum,222 and is claimed by Seidelin to be the causal agent of yellow fever.
Paraplasma flavigenum occurs in the early days of the disease as small chromatin granules with or without a faint trace of cytoplasm. The bodies are usually intracorpuscular. Also, somewhat larger forms, with distinct cytoplasm, are seen in small numbers. During the later days of the disease still larger forms are found, and these occur also in sections of organs (e.g., kidney) made post-mortem. Some of these larger forms are perhaps schizonts. In the second period of the disease possible micro- and macro-gametes may be found, some of which are extracorpuscular. Some small free bodies have been seen. Recently schizogony has been stated to occur in the lungs, and it is said that guinea-pigs can be inoculated with Paraplasma flavigenum, and show yellow pigment in the spleen.
Seidelin places Paraplasma in the BabesiidÆ, with resemblances more particularly to Theileria. V. Schilling-Torgau and Agramonte have criticized these findings; the former considers them to be the resultant of certain blood conditions.
P. subflavigenum was found by Seidelin in 1912 in a man suffering from an unclassified fever in Mexico.
Further, it is now known that a Paraplasma occurs naturally in guinea-pigs. More researches are needed on these matters, as some writers (e.g., Wenyon and Low) claim that the bodies are not organismal.
Paraplasma flavigenum.—The Yellow Fever Commission (West Africa) in their third report, dated 1915, have come to the conclusion that there is no evidence that the bodies termed Paraplasma flavigenum are of protozoal nature or that they are the causal agents of yellow fever.
Sub-class. NEOSPORIDIA, Schaudinn.
Sporozoa in which growth and spore formation usually go on together.
Order. Myxosporidia, BÜtschli.
These parasites, which were discovered by Johannes MÜller (1841), live principally in fishes, and occasionally cause destructive epizoÖtics amongst their hosts. MÜller first observed them in the form of whitish-yellow pustules on the skin or on the gills of various fishes. These pustules contained masses of small shell-covered bodies with or without tails (“psorosperms,” see fig.93). Similar bodies were also found in the air bladders of certain fish. Creplin (1842) demonstrated the resemblance of the cysts (“psorosperm tubes”) harbouring the psorosperms to the “pseudonavicella-cysts” of a gregarine, as described by v. Siebold. Dujardin (1845) considered that there was possibly some connection between the protoplasmic “psorosperm tubes” and the spores they contained, and the developmental stages of monocystid gregarines from the vesiculÆ seminales of earth-worms. The relationship of the “fish psorosperms” was placed on a firmer basis by Leydig (1851) and LieberkÜhn. The former found numerous forms in marine fish, and he discovered in species which live free in the gall bladder of cartilaginous fishes that the psorosperms originated in a manner similar to the gregarines. LieberkÜhn (1854) studied the Myxosporidia in the bladder of the pike (fig.93, a, b, d), and observed their amoeboid movements, as well as the formation of the spores, from each of which a small amoeboid body escaped, a discovery that was confirmed by Balbiani. The same author also found that spiral filaments were enclosed in the so-called polar body, i.e., the polar capsule of the psorosperm spores, and that these could be protruded (fig.93, d, and fig.95).
Fig. 93.—Upper figure, part of a gill of a roach, Leuciscus rutilus (natural size), with two myxosporidia. Lower figures, a, b, d, spores of myxosporidia from a pike, Esox lucius. c, Spore from Platystoma fasciatum. (After J. MÜller.)
Fig. 94.—The tailless spore of Myxobolus mÜlleri, with the polar bodies and their nuclei and the sporozoite. (After BÜtschli.)
The term Myxosporidia, which at the present day is universally applied to the “psorosperm tubes,” was introduced by BÜtschli in 1881, who studied not only the structure and development of the spores, but also the protoplasmic body of the
Fig. 95.—Schematic representation of a spore of Myxobolus. One polar capsule has protruded its filament; two nuclei and a “vacuole” in the sporozoite. (After Doflein.)
Fig. 96.—Chloromyxum leydigi. Active trophozoite (parasitic in gall-bladder of skates, rays, dog-fish). Ect, ectoplasm; ps, pseudopodia; end, endoplasm; y, yellow globules in endoplasm; sp, spores, each with four polar capsules. ×525. (After ThÉlohan.)
The Myxosporidia live either free on the epithelial surface of hollow organs (gall or urinary bladder, renal tubules, but never in the intestine), or are enclosed in the tissues of their host. The gills and muscular system are their favourite habitat, but other tissues or organs may be attacked. Species of Myxosporidia are also known from Amphibia, Reptilia, and a few invertebrates.
The free forms, which are often amoeboid (fig.96), move by the aid of variously shaped pseudopodia, have a constant form, or may exhibit contractions of the body. The tissue parasites often reach a considerable size, so that the integument of the host forms protuberances over them. They are of a roundish or irregular shape. Frequently they are enveloped in a connective tissue covering formed by the host.
The protoplasmic body in the trophic phase (fig.96) shows a distinct ectoplasm which is finely granular or sometimes striated, and an endoplasm which is coarsely granular and contains many nuclei as well as cell inclusions, such as crystals, pigment grains and fat globules. The nuclei originate by division from the primitive nucleus of the amoeboid germ that issues from the spore. This amoebula may or may not live intra-cellularly during the early stages of its existence.
The multinucleate trophozoite of a Myxosporidian forms spores in its endoplasm practically throughout its whole period of growth (fig.96). Vegetative reproduction by a process of external budding or plasmotomy may also occur, as in Myxidium lieberkÜhni from the urinary bladder of the pike.
The myxosporidian trophozoite may produce two spores within itself, when it is placed in the sub-order Disporea, or it may produce numerous spores, which is characteristic of the sub-order, Polysporea. The phenomenon of spore formation
Spore formation is usually very complicated and there are differences of opinion as to the interpretation of various stages, particularly as to whether conjugation occurs therein. The process is initiated by the concentration of cytoplasm around one of the nuclei of the endoplasm, so that a small spherical mass or initial corpuscle is produced, the pansporoblast (Gurley) or primitive sphere (ThÉlohan). Some authors state that a pansporoblast really results from a conjugation of two initial corpuscles (fig.97, A-D). Nuclear multiplication occurs within the pansporoblast (fig.97, E), and sooner or later two multinucleate sporoblasts are formed within it (fig.97, F). Each sporoblast gives rise to a single spore, which consists of a sporocyst or envelope composed of two valves each secreted by a cell, two polar capsules each secreted by a cell, and the sporoplasm or amoebula which becomes binucleate (fig.97, G). During the process of spore formation (fig.97) various vegetative and reduction nuclei may be produced, in addition to those which are essentially involved in spore formation, and the sporocyst cells may be developed early.
Fig. 97.—Myxobolus pfeifferi. Spore formation. A, reproductive cell from plasmodial trophozoite; B, cell divided unequally into two; C, smaller cell forming envelope to larger one; D, pansporoblast formed by union of two forms like C; E, multinucleate pansporoblast, two of the nuclei being those of the envelope; F, pansporoblast divided into two multinucleate sporoblasts; G, spore differentiation; p, two parietal cells forming sporocyst; bc, polar capsules; am, binucleate amoebula; H, ripe spore in which the two nuclei of the amoebula have fused. (After Keysselitz.)
Each spore contains two (figs.94, 95) or more polar capsules which are clearly visible in the fresh condition. Each polar capsule is a hollow, more or less pear-shaped body, secreted by a cell and having a well defined contour. Within it, a long, delicate, elastic filament, the polar filament, is formed, and lies spirally coiled in the polar capsule until just before the emergence of the amoebula from the spore (fig.95). The polar filament is ejected, probably under the influence of the digestive
The spores fulfil the purpose of effecting transmission to other hosts. Infection occurs by the ingestion of the parasites per os after their escape by some means from their host. ThÉlohan and others have demonstrated that the valves of the spores soon open under the influence of the digestive juices, thus allowing the young myxosporidia to escape. Their further history is unknown; but it may be surmised that they either travel direct to the organs usually affected (gall bladder, urinary bladder), or are distributed in the body by means of the circulatory or lymphatic systems.
The Myxosporidia that invade tissues are often deadly to their hosts. They may be present in a state of “diffuse infiltration” when practically every organ of the body may be infected, as in barbel disease (due to Myxobolus pfeifferi). On the other hand, the parasites may be concentrated at one spot, when cysts, either large or small, are produced. Such cysts occur on the gills of many fishes. A few additional important pathogenic forms are Myxobolus cyprini, the excitant of “pockenkrankheit” of carp, and Lentospora cerebralis, parasitic in the skeleton of SalmonidÆ and GadidÆ. The skeletons of the tail, fins and skull particularly are seats of infection, and from the skull the Lentospora can spread to the semicircular canals, resulting in loss of power to maintain its balance on the part of the fish. On this account the malady is termed “drehkrankheit.” Young fish are more particularly infected. Myxobolus neurobius infects the spinal cord and nerves of trout.
Myxosporidia are divided into two sub-orders—Disporea and Polysporea—according to whether they form only two or several spores during their growth. The former include two genera limited to fishes, which are easily distinguishable by the shape of the spores: Leptotheca, ThÉl., with a rounded spore, and Ceratomyxa, ThÉl., with a very elongate spore. The larger number of genera belong to the Polysporea, which are divided into three families:
| (1) Amoeboid germ with a vacuole the contents of which do not stain with iodine. | (a) With two polar capsules.—MyxidiidÆ. | |
| (b) With four polar capsules.—ChloromyxidÆ. | ||
| (2) Amoeboid germ with a vacuole stainable with iodine. Spores with two polar capsules.—?MyxobolidÆ. | ||
| For further subdivisions the differences in the spores are principally utilized. | ||
Order. Microsporidia, Balbiani.
These are the organisms discovered in the stickleback by Gluge in 1834, and in Coccus hesperidum by Leydig in 1853. They have since been found in numerous other arthropods, especially insects. They acquired particular importance when it was discovered that they were the cause of the “pÉbrine” disease (“gattina” of the Italians) which caused so much destruction amongst silkworms (Bombyx mori). Pasteur (1867–70) and especially Balbiani (1866) participated in the researches on Nosema bombycis, and it was the latter who classed the “pÉbrine bodies” or “psorospermia of the arthropoda” amongst the Sporozoa as Microsporidia (1882).223 The complete life cycle of N. bombycis was described in 1909 by Stempell. The Microsporidia are not confined to insects and arachnoids, they are now known to occur also in crustacea, worms, bryozoa, fishes, amphibians and reptiles. Certain tumours in fishes, similar to those formed by many Myxosporidia, are produced by Microsporidia. Fantham and Porter found that Nosema apis was pathogenic to bees
The Microsporidia, as their name implies, form minute spores which usually are oval or pear-shaped. Each spore contains a single polar capsule which is not easily visible in the fresh state (fig.98, f) and a single amoeboid germ issues from the spore (fig.99, b).
Fig. 98.—Nosema apis. Various stages in life-cycle. a, planonts or amoebulÆ from chyle stomach of bee; b, amoeboid planont creeping over surface of gut epithelial cell; c, uninucleate trophozoite within epithelial cell; d, meront with nucleus divided into four, about to form four spores; e, epithelial cell crowded with spores; f, young spore; g, spore showing five nuclei, polar filament ejected, and amoebula, about to issue. ×1,500, a-e; ×2,150, f-g. (After Fantham and Porter.)
The life cycle of Nosema apis, parasitic in bees, may be taken as an example of that of a microsporidian. The infection of the host is initiated by the ingestion of spores of N. apis in food or drink contaminated with the excrement of other infected bees. Under the influence of the digestive juice of the bee the spore-coat (sporocyst) softens, the polar filament is ejected and anchors the spore to the gut epithelium, and the minute amoebula contained in the spore emerges. The amoebula is capable of active amoeboid movements (fig.98, b) and so is termed the planont or wandering form (fig.98, a). After a short time each planont penetrates between or into the cells of the epithelium of the gut, a few only passing through into the body cavity. Within the cells the amoebulÆ become more or less rounded, lose their power of movement, and after a period of growth of the trophozoite (fig.98, c) commence to divide actively, these dividing forms being known as meronts (fig.98, d). Various forms of fission occur, and during this phase, termed merogony, the numbers of the parasite within the host are greatly increased, with concomitant destruction of the epithelium (fig.98, e). After a time sporogony commences. The full-grown meront becomes successively the pansporoblast and sporoblast. Nuclear multiplication and differentiation ensue and five nuclei are ultimately produced. At the same time a sporocyst is secreted, and two vacuoles are produced within. One is the polar capsule, and
Fig. 99.—a, section through the abdominal wall of a silkworm, whose epithelial cells contain Microsporidia (Nosema bombycis); b, a spore, the contents of which are escaping. (After Balbiani.)
Fig. 100.—Nosema bombycis, Naeg. Spores treated with nitric acid, thus rendering the polar capsule perceptible, and the filament has protruded from one of the spores. (After ThÉlohan.)
A trophozoite (meront) of N. apis becomes a single pansporoblast which gives rise to one sporoblast producing one spore, and this procedure is characteristic of the genus Nosema. In other genera the trophozoite may form more than one pansporoblast and each pansporoblast may form a variable number of spores in different cases. Various attempts at classification have been based on these characteristics. It must suffice here to note that in the cases where the trophozoite becomes one pansporoblast, the latter can produce four spores in the genus Gurleya, eight spores in ThÉlohania and many spores in Pleistophora. In other cases, where the trophozoites give rise to many pansporoblasts, each of the latter may form many spores, as in the genus Glugea.
A few pathogenic microsporidian parasites other than N. apis may be mentioned. N. bombycis, causing pÉbrine in silkworms, may infect any or all the tissues of the host (fig.99). The larvÆ of the host, i.e., the “silkworms,” may become infected by eating food contaminated with spore-containing excrement of already infected silkworms. In cases of heavy infection the silkworm dies, but should the infection be less intense the larva becomes a pupa in which the parasite persists, so that the moth emerges from the cocoon already infected. Not only is the moth parasitized itself, but the Nosema reaches the generative organs of both sexes and penetrates the ovaries of the female, with the result that the ova are deposited infected. Such infected eggs are capable of developing, so that infection may be transmitted hereditarily as well as by the contaminative method. Infected eggs can be recognized by microscopic examination, as Pasteur showed, and thus preventive measures may be adopted.
A microsporidian parasite is known to occur on the roots of the spinal and cranial nerves of Lophius piscatorius, the angler fish. This parasite is variously referred to the genera Nosema and Glugea.
ThÉlohania contejeani, parasitic in the muscles of crayfish, is believed by some to be the causal agent of recent epizoÖtics among them, though others believe the disease to be really due to a bacillus. It may be that the one organism aids in the entry of the other into the host.
Order. Actinomyxidia, Stolc.
Fig. 101.—Spore of Hexactinomyxon psammoryctis. At top of figure three polar capsules, one with polar filament extended. ×450. (After Stolc.)
A brief mention may be made of the Actinomyxidia (fig.101), which were first described by Stolc in 1899 as parasites of OligochÆtes. They have also been investigated by Mrazek, and a detailed study of certain species was made by Caullery and Mesnil (1905). The trophozoite is small and amoeboid. The spores are large, and exhibit tri-radiate symmetry. Spore formation is complicated and sexual processes occur therein. Many amoebulÆ are set free from each spore.
Order. Sarcosporidia, Balbiani.
The first member of this group was discovered by Miescher in 1843. This author found white filaments running parallel with the direction of the fibres in the voluntary muscles of mice. They were visible to the naked eye, and proved to be cylindrical tubes tapering at each end. They were as long as the muscular fibres, were enveloped in a membrane, and contained innumerable elongate or kidney-shaped bodies and a smaller number of little spherical forms. Th. v. Hessling confirmed (1853) the occurrence of these “Miescher’s tubes” within the muscular fibres, this author having discovered the same structures in the heart muscles of deer, cattle, and sheep. Both investigators considered them to be pathological transformations of the muscles. v. Siebold, from his own experiences, regarded them as fungus-like entophytes.
Rainey (1858) discovered similar structures in the muscular system of pigs, and considered them to be early stages of Cysticercus cellulosÆ, which error Leuckart rectified, simultaneously emphasizing their relationship with Myxosporidia. Both these authors found them in the muscular fibres, and both observed that they possessed a thick striated membrane. Manz (1867) published the results of more minute investigations on the structure and contents of the cylinders. This observer also recognized the disease in rabbits and attempted to cultivate the parasites. He also tried to induce experimental infection in guinea-pigs, rats, and mice, but the result was negative.
However, domestic and wild mammals are not the only hosts of Sarcosporidia; these parasites are also harboured by birds. Thus, according to KÜhn, they are found in the domestic fowl; according to Rivolta in Turdus, Corvus, and other birds; according to Stiles in North American birds; while Fantham found Sarcosporidia in the African mouse-bird, Colius. Reptiles also are parasitized occasionally. Bertram found them in the gecko, LÜhe in the wall-lizard. It was found also that the Sarcosporidia could develop not only in the muscles but also in the connective tissue. This led to the foundation of a new, but provisional, classification by Blanchard, using the generic name Miescheria for the parasites in the muscles and Balbiania for those in the connective tissue. Finally, Sarcosporidia have also been observed in man.
The relation of these parasites to certain diseases of domestic animals has been studied by veterinary surgeons. Sarcosporidia may cause fatal epizoÖtics among sheep.
There is still a wide field open for research in regard to the structure and development of these parasites, and the manner in which the hosts become infected.
Fig. 102.—Longitudinal section of a muscle of the domestic pig, with Sarcocystis miescheriana. ×30. (After KÜhn.)
Fig. 103.—Transverse section of the muscle of a pig, with Sarcocystis miescheriana. ×38. (After KÜhn.)
The Sarcosporidia usually appear as elongate, cylindrical, or fusiform bodies, rounded at both extremities and of various lengths and breadths (fig.102). In some species they may be from 16mm. to 50mm. long, as in the sheep and roebuck. These bodies are the so-called sarcocysts or Miescher’s tubes. They lie in transversely striated muscular fibres which they distend more or less. The forms found in the connective tissue are apparently parasites which originally inhabited the muscular fibres, and only on disintegration of the fibres reached the connective tissue, where they grow to large oval or globular bodies (fig.105). The mammalian muscles usually infected are those of the oesophagus, larynx, diaphragm, body-wall, and the psoas muscles. The skeletal muscles may be affected in acute cases, as well as those of the tongue and eye. The heart muscles are sometimes parasitized.
In fresh material cut into thin slices the parasites are frequently recognizable, even with the naked eye, because of their yellowish-white colour. Under the microscope they appear to be coarsely granular (fig.103). Beginners may find some difficulty in distinguishing them from other foreign bodies, such as dead and calcified encapsuled TrichinÆ, or from Cysticerci that have died and become calcified in the early stages, more particularly as the Sarcosporidia also occasionally may become calcified.
Fig. 104.—Sarcocystis miescheriana from pig. Late stage in which body is divided into numerous chambers or alveoli, each containing many spores. (From Wasielewski, after Manz.)
The Sarcosporidia are always enveloped in a membrane, which is probably formed at an early stage. In a few cases it remains thin
In the youngest Sarcosporidia (40µ in length) from the muscles of the sheep there occur, according to Bertram, small roundish or oval cells (4µ to 5µ), the nuclei of which are half their size, and are embedded in a granular protoplasmic mass. In somewhat larger, and therefore older, cylinders, the investing membrane of which already shows both layers, the cells have become larger (to 7µ) and are more sharply outlined from each other (fig.106). These uninucleate cells may be considered as pansporoblasts. In each pansporoblast division of the nucleus occurs (fig.107), and meanwhile the pansporoblasts become isolated within the chambers, the dividing partitions of which originate from the granular protoplasm which is present between the pansporoblasts. The numerous uninucleate daughter forms produced within the chambers become spores direct (fig.108).
The process commences in the centre of the cylinders or sarcocysts, and then progresses towards the extremities, the parasites meanwhile increasing in size, and new pansporoblasts being continually formed at the extremities (fig.107).
Fig. 105.—Transverse section of Sarcocystis tenella, Raill. From the oesophagus of the sheep, Ovis aries. ×38. a, marginal chambers filled with spores; b, connective tissue of the oesophagus; c, muscles of the oesophagus.
Fig. 106.—Young Sarcocystis tenella of the sheep, 47µ in length. (After Bertram.)
Fig. 107.—End of a trophozoite of Sarcocystis miescheriana from the diaphragm of the pig, showing division in pansporoblasts. ×800. (After Bertram.)
Fig. 108.—Sarcocystis blanchardi of the ox. Longitudinal section of sarcocyst or Miescher’s tube. a, substance of muscle fibre; b, envelope of sarcocyst; c, muscle nuclei; d, spores in chambers; e, ground substance. ×400. (From Wasielewski, after van Eecke.)
The spores (sometimes called Rainey’s corpuscles), vary in shape according to the species, but are also of different form individually. They are mostly kidney-, bean- or sickle-shaped (fig.109), and of small size, sometimes reaching 14µ by 3µ to 5µ. They are apparently surrounded by a thin membrane, and at one extremity (according to the discovery of L. Pfeiffer, confirmed by van Eecke,
Fig. 109.—Spores of Sarcocystis tenella, Raill. a, fresh, showing the polar capsule; b, stained, showing metachromatic granules and nucleus. ×1,000. (After Laveran and Mesnil.)
The gymnospores of Sarcocystis muris, from the mouse, show active boring movements when kept in saline solution warmed to 35° or 37°C. S. muris is very deadly to its host. From their structure the spores do not appear to have great powers of resistance to external conditions. They measure 12µ by 3µ to 4µ or less.
Laveran and Mesnil (1899) isolated a toxin from S. tenella of the sheep and called it sarcocystin. This substance is especially pathogenic to experimental rabbits.
The duration of life of the Sarcosporidia is a comparatively long one. The affected muscular fibres may remain intact and capable of performing their functions for a long time, but at last they perish, if the host lives long enough. Thus the Sarcosporidia of the muscles are then enveloped only by sarcolemma, and finally, when this likewise disappears, they fall into the intra-muscular connective tissue. In many cases the Sarcosporidia die off within their hosts, this, according to Bertram, being brought about by a disintegration of the spores in the central chambers. In other cases the leucocytes play a part in the destruction of the Sarcosporidia, and sometimes it happens that lime salts are deposited in and around the vacant cylinders.
In some places pigs, sheep, mice and rats are infected with sarcosporidiosis to a remarkable extent, in certain cases almost reaching 100 per cent. Young animals also are infected, and perhaps infection only takes place during youth.
Although the natural mode of transmission of the Sarcosporidia remains to be determined, yet various experimental researches on the problem are of interest and importance. Theobald Smith (1901) found that mice could be experimentally infected with S. muris by feeding them with the flesh of other infected mice. The incubation period was a long one, namely forty to fifty days. Thus, on the forty-fifth day after feeding young Sarcosporidia were found, and seventy days after feeding spore formation began. Ripe spores were found two and a half to three months after the commencement of
According to Erdmann228 (1910) the Sarcosporidian spore germinates in the intestine of the host, which has recently ingested infected material. The spore liberates its contained toxin—sarcocystin—which acts upon the adjacent intestinal epithelium, whereby the latter is shed, and an amoebula creeps out of the spore. The amoebula is able to penetrate the denuded area and get directly into the lymph-spaces of the submucous coat of the intestine. The first period of development, lasting some twenty-eight to thirty days, is said to be passed in the lymph-spaces of the intestine. Later the amoebula reaches a muscle fibre. Writing in May, 1914, Erdmann229 records the appearance of small amoeboid and schizogony forms six days after infection of the host. Crawley230 (1913) controverts some of these statements and considers that the Sarcosporidian spore, still sickle-shaped, bores its way into the epithelial cells of the intestine and comes to rest there. The spore then becomes round or elliptical, and peripheral masses of chromatin appear within it, suggesting schizogony. This happens about twelve hours after feeding, and in twenty-four hours the spores appear to have left the intestine. More recently (May, 1914), Crawley231 considers that there is sexual differentiation among the Sarcosporidian spores, a few hours after their ingestion by the host.
Interesting discussions have occurred as to the site of the toxic sarcocystin within the spore. Metachromatic granules occur in the middle of the Sarcosporidian spore (fig.109), and the toxin may be contained in these grains, as they disappear, according to Erdmann, before the amoebula penetrates the denuded intestinal wall. However, a polar capsule, containing a polar filament, may be present at one end of a Sarcosporidian spore. Laveran and Mesnil described a striated area at the more pointed end of the spore of S. tenella, which area they consider to represent a polar capsule. Fantham232 (1913)
Again, various authors have stated that Sarcosporidian spores may occur in the blood of the host at times. If so, then an intermediate host may be concerned in their transmission. Perrin suggested that Sarcosporidia might be spread by blow-flies and flesh-flies.
The classification of the Sarcosporidia as proposed by R. Blanchard, which was based on their various habitats, can no longer hold, because the same species may occur in the muscles as well as in the connective tissue. For the present, the few species that are known may be placed in one genus, Sarcocystis, Ray Lankester, 1882.
The following species of Sarcocystis are of interest:—
S. miescheriana, KÜhn, 1865, in the pig.
S. bertrami, Doflein, 1901, in the horse.
S. tenella, Railliet, 1886, in sheep. S. tenella bubali in buffaloes in Ceylon and Egypt.
S. blanchardi, Doflein, 1901, in cattle.
S. muris, Blanchard, 1885, in the mouse, to which it is lethal.
S. hueti, Blanchard, 1885, in the seal.
S. colii, Fantham, 1913, in the African mouse-bird, Colius erythromelon.
Also various Sarcosporidia from antelopes, monkeys, opossum, birds, the gecko and wall-lizard are known.
The spores of S. muris, S. bertrami, S. tenella, and S. colii can multiply by longitudinal fission.
Sarcosporidia observed in Man.
(1) Lindemann233 found on the valves and in the myocardium of a person who had died of dropsy certain brownish masses, 3mm. in length and 1·5mm. in breadth which he regarded as gregarines. If these were actually independent animal organisms it may be suggested that they were Sarcosporidia. Rivolta (1878) named the species S. lindemanni.
(2) Rosenberg234 found a cyst 5mm. in length and 2mm. in breadth in a papillary muscle of the mitral valve of a woman, aged 40, who had died from pleuritis and endocarditis. The cyst contained no scolex nor hooklets of tÆnia. Numerous small refracting bodies, round, oval or kidney-shaped, were found in a daughter cyst, as well
(3) Kartulis235 observed Miescher’s cylinders of various sizes in the liver (?) and in the muscular system, of a Sudanese who had succumbed to multiple abscesses of the liver and abdominal muscles. This may be considered as the first actual case of the occurrence of Sarcosporidia in man. Koch in 1887 described a case in Egypt.
(4) The case reported by Baraban and St. Remy236 was at once demonstrated as certain. It related to a man who had been executed, and in the laryngeal muscles of whom Sarcosporidia were found; the length of the parasites varied between 150µ and 1,600µ, their breadth between 77µ and 168µ. The affected muscular fibres were distended to four times their normal thickness. This species was described by Blanchard as “Miescheria” muris, but according to Vuillemin, it was more probably Sarcocystis tenella of the sheep.
(5) Vuillemin has also described a case of Sarcosporidia found in the muscles of a man who died from tubercle at Nancy. The author considered that the parasite corresponded to S. tenella.
(6) Darling237 (1909) found Sarcosporidia in the biceps of a negro from Barbados.
The Myxosporidia, Microsporidia, Actinomyxidia and possibly the Sarcosporidia may be included within the section Cnidosporidia (Doflein), since they possess spores containing polar capsules.
Order. Haplosporidia, Caullery and Mesnil.
The Haplosporidia are a group of organisms having both a simple structure and life-history. The simplicity may represent a primitive condition or may be due to degradation resultant on parasitism, and thus it is possible that the group is not a homogeneous one. The order Haplosporidia was created by Caullery and Mesnil in 1899, and includes parasites of rotifers, annelids (fig.110), crustacea, fish, prochordates and man. They may be present in the body cavity or alimentary tract, and can also occur in the septum nasi of man, in the nervous system of Cephalodiscus, and in tumours of fish.
As the name implies, the spores of the Haplosporidia are simple, without polar capsules, and are uninucleate. In some genera, e.g., Haplosporidium, Urosporidium (fig.111) there is a spore-coat or sporocyst which may be elongate or spiny. The developmental cycle of a Haplosporidian, such as Haplosporidium or Bertramia, begins with a small, uninucleate cell, often rounded, possessing a cell membrane that may be prolonged into processes. Growth takes place, coupled with an increase in the number of nuclei, so that a multinucleate trophozoite is produced. Later, this
More recently (1905–1907) two important organisms have been described and included in this group, namely, Neurosporidium cephalodisci238 (Ridewood and Fantham) from the nervous system of the prochordate, Cephalodiscus nigrescens, and Rhinosporidium kinealyi (or seeberi) from the septum nasi of man. In the case of Rhinosporidium and Neurosporidium, after the uninucleate spore has grown into a multinucleate trophozoite, the latter segments into uninucleate pansporoblasts, as in the preceding cases. A difference then occurs, for each pansporoblast enlarges, its nucleus divides and a “spore-morula” is formed. Thus a multinucleate pansporoblast or spore-morula, divided into many uninucleate sporoblasts (spore mother cells) is produced, and each sporoblast without further change becomes a uninucleate spore.
The Haplosporidia have therefore been divided by Ridewood and Fantham (1907)239 into two sections:—
(1) The Polysporulea, wherein the pansporoblast gives rise to a number of spores (nine or more), e.g., Rhinosporidium, Neurosporidium.
(2) The Oligosporulea, wherein the pansporoblasts give rise each to a few (four) spores or to only a single spore, e.g., Haplosporidium, Bertramia, Coelosporidium, Ichthyosporidium.
Fig. 110.—Haplosporidium heterocirri. Section throughout wall of the PolychÆte worm, Heterocirrus viridis, showing various developmental stages of the Haplosporidium. ×550. (After Caullery and Mesnil.)
Fig. 111.—Haplosporidian spores. a, b, Haplosporidium heterocirri. a, fresh; b, after immersion in sea water; c, d, Urosporidium fuliginosum. ×1000. (After Caullery and Mesnil.)
Rhinosporidium kinealyi, Minchin and Fantham, 1905.
Rhinosporidium kinealyi, parasitic in man, must now be considered in greater detail. This organism was found in nasal polypus in India, and has since been recorded from the ear as small nodules in the external auditory meatus. The Indian cases came from the
The Rhinosporidium polypus is said not to be particularly painful, though nasal forms must interfere with breathing to some extent. The first nasal polyp reported from India formed a vascular pedunculated growth on the septum nasi and was about the size of a large pea or raspberry. It was compared with a raspberry, being red in colour with a number of small whitish dots upon its surface. When the tumour was cut, a number of similar whitish dots were seen within. These were the cysts of Rhinosporidium. According to Minchin and Fantham240 (1905), they vary considerably in size and measure up to 200µ or 250µ in diameter. Each possesses a cyst wall which varies in thickness in different cysts. Its outer wall is always firm and distinct, the inner limit being less definite at times. Each large cyst is filled with numbers of spherical or oval bodies, showing every gradation between small ones at the periphery and large ones at the centre (fig.112). Roughly, three zones of parasites can be distinguished in a large cyst, a peripheral set consisting of the youngest parasites, an intermediate group and a central, oldest zone. A large cyst may possess a pore for the egress of its contents. Some of the cysts show polar distribution of the zones.
The youngest forms of Rhinosporidium are difficult to detect. They are small, granular masses, round, ovoid or irregular and at times even amoeboid in appearance. These are young trophozoites. They increase in size, but encystment occurs early, the outer layer becoming firm so that the organisms have a definite contour. Each is soon multinucleate and the cytoplasm segments around the nuclei. The cyst thus becomes full of uninucleate pansporoblasts or sporonts, with a peripheral layer of undifferentiated protoplasm. The pansporoblasts grow in size. In the larger cysts the formation of pansporoblasts progresses at the expense of the peripheral layer of protoplasm, which, however, continues to grow, so that the cyst as a whole increases in size. The pansporoblasts at first are uninucleate (fig.112, a), and then undergo nuclear multiplication. This is well seen in the intermediate zone of parasites, where the pansporoblasts show first one, then two, then four or more spores (fig.112, b), while in the oldest centrally placed pansporoblasts, about a dozen or sixteen closely packed spores (fig.112, c), can be seen. The spore is small and rounded, and its nucleus is clear and distinct. The fully formed pansporoblast or spore morula becomes surrounded by a membrane.
Fig. 112.—Rhinosporidium kinealyi. Portion of ripe cyst containing pansporoblasts of various ages. ×480. (After Minchin and Fantham.)
Certain of the cysts have been found in a ruptured condition,
The Asiatic specimens of R. kinealyi were first described in detail by Minchin and Fantham (1905) from material briefly reported to the Laryngological Society of London in 1903, by O’Kinealy. Material obtained by Dr. Nair, of Madras, was described by Beattie241 in 1906. This material came from Cochin. Castellani and Chalmers have found similar polypi in Ceylon.
Wright242 has described the parasite from Memphis, Tennessee. Seeber243 in 1896 described nasal polypi in Buenos Ayres, and in 1900 Wernicke named the parasite therein Coccidium seeberi. Seeber’s parasite is a Rhinosporidium, R. seeberi, and may ultimately be found to be the same as R. kinealyi. Ingram244 reports Rhinosporidium cysts, with pores in the cyst walls, in conjunctival polypus and in papilloma of the penis in India. Zschokke has reported the presence of Rhinosporidium in horses in South Africa.
Class IV. INFUSORIA, LedermÜller, 1763.
The Infusoria (or Heterokaryota, Hickson, or Ciliophora, Doflein) include the Ciliata and the Suctoria. A few authorities, including Braun, raise the Suctoria (or Acinetaria) to separate rank as a class, but this is not widely followed.
The body of the Ciliata usually is bilaterally symmetrical and is enveloped in a cuticle which has numerous openings for the protrusion of the cilia. Most kinds have a fixed shape, whilst changes in the form of others are brought about by the contractions of the body substance. The latter exhibits hyaline ectoplasm, in which myonemes, and occasionally also trichocysts (minute spindle-shaped bodies) appear, and granular endoplasm which may contain numerous vacuoles. The cilia, on whose various arrangements the classification is based, are always processes of the ectoplasm. Their form varies; they may be hair-like, or more rarely thorn-like, spur-like, or hook-shaped; undulatory membranes also may occur, which are probably composed of fused cilia.
With the exception of some of the parasitic species, an oral cavity, peristome or cytostome, is always present. It is frequently beset with cilia or provided with undulatory membranes, which help to waft the food inwards; sometimes there is an anal aperture (cytopyge) generally placed at the opposite pole of the organism. A cytopharynx fringed with cilia or sometimes with a specialized supporting apparatus is connected with the peristome. Vacuoles form round the ingested food, and in many species a constant rotation goes on in the endoplasm. Often one, and sometimes two contractile vacuoles are present, the frequency of the pulsations of which depends on the surrounding temperature. Sometimes special conducting channels lead to the vacuoles, or there are outlet channels leading to the exterior.
There is in almost every case a large nucleus (macronucleus), and lying close up to it a small nucleus (micronucleus). The form of the large nucleus varies according to the species. Numerous nuclei are not very common, but these occur in Opalina, which lives in the hind-gut of amphibia, and is also distinguished by the absence of an oral aperture.
Reproduction is effected by binary fission; less commonly, after encystment, by multiple division, or by budding. The divisions can be repeated many times, but finally cease, and then the conjugation of two specimens brings about a regeneration, particularly of the nuclei. Numerous examinations (BÜtschli, Hertwig, Maupas, Calkins) have demonstrated that after two individuals have associated by homologous parts of the body, the micronucleus separates from the macronucleus, becomes larger and divides twice by mitosis, so
Encystment amongst the Infusoria is very general, and is essentially a means of protection when the surrounding medium dries up. Doubtless these cysts are frequently carried long distances by the wind, which explains the wide geographical distribution of most species. Also, multiplication often takes place in the encysted condition.
Some Infusoria live a free life, others are sedentary; the latter form colonies in fresh as well as in salt water. Numerous species are parasites of various lower and higher animals,245 and a few also are parasitic in man.
The Prague zoologist, v. Stein, introduced a classification of the Infusoria that has been almost universally adopted. It is founded on the different position of the cilia on the body. Though, no doubt, artificial, it is a convenient system. BÜtschli has compiled a better one.246 But for our purpose Stein’s system is sufficient:—
Order 1. Holotricha, Infusoria with cilia that are evenly distributed over the entire body.
Order 2. Heterotricha, ciliated all over like the Holotricha, but having stouter cilia about the peristome.
Order 3. Hypotricha, only ciliated on the ventral surface.
Order 4. Peritricha, with only a ring of spiral cilia, mostly sedentary.
The Infusoria observed in man belong to the order Heterotricha, with few exceptions.
Genus. Balantidium, ClaparÈde et Lachmann.
Heterotrichous Infusoria of oval or bag-like form and almost circular on transverse section; the anterior extremity narrowed, the posterior end broad and rounded off, or also narrowed; the peristome starting at the anterior end is broadest there and becomes narrower as it gradually obliquely approaches towards the posterior extremity. There are coarse cilia along the entire left border and the anterior part of the right border. Longitudinal striation is distinct and regular. There are two contractile vacuoles on the right, and occasionally also two or more to the left. The anus (cytopyge) is terminal. The macronucleus is usually horse-shoe or kidney-shaped, sometimes oval; the micronucleus contiguous. Reproduction is by binary fission and conjugation, and encystment occurs. The cysts are spherical or oval. These ciliates are parasitic in the large intestine of human beings and pigs, in Amphibia, and in the body cavity of polychÆte Annelida.
Fig. 113.—Balantidium coli. a, nucleus; b, vacuole; c, peristome; d, bolus of food. (After Leuckart.)
Fig. 114.—Balantidium coli, free and encysted; a, anus or cytopyge; n, macronucleus; b, bolus of food. (After Casagrandi and Barbagallo.)
Balantidium coli, Malmsten, 1857.
Syn.: ParamÆcium coli, Malmsten, 1857.
The body is oval, 60µ to 100µ in length (up to 200µ according to Janowski), and 50µ to 70µ in breadth. The peristome is funnel-shaped or contracted, the anterior end being then broadened or pointed according to the degree of contraction (figs.113, 114). The ecto- and endo-plasm are distinct, the latter is granular, containing drops of fat and mucus, granules of starch, bacteria, and occasionally
Balantidium coli lives in the large intestine of man, in the rectum of the domestic pig, and has been found in monkeys. It propagates by transverse division, but conjugation and encystment are known to take place.247 Transmission to other hosts is effected by the cysts of the parasite (fig.114).
Balantidium coli, first seen by Leeuwenhoek, was described by Malmsten in 1857 in a man aged 35 years, who had two years previously suffered from cholera, and since then had been subject to diarrhoea. The examination showed an ulcer in the rectum above the mid sphincter ani, in the sanguineous purulent secretion of which numerous Balantidia were swimming about. Although the ulcer was made to heal, the diarrhoea did not cease and the stools contained numerous Balantidia, the number of which could only be decreased by extensive enemas of hydrochloric acid.
The second case related to a woman who was suffering from severe colitis, and who died ten days after admission. The malodorous, watery evacuations contained innumerable Balantidia, in addition to pus, and at the autopsy the anterior portion of the large intestine was found to be infested with them.
Subsequently this parasite has often been observed in human beings, and various cases have been recorded. These occurred in Russia, Scandinavia, Finland, Cochin China, Italy, Germany, Serbia, Sunda Islands, Philippine Islands, China, and in other parts of Asia and in America. Other cases were reported by Askanazy, Ehrnroth, Klimenko, Nagel, Koslowsky, Kossler, Waljeff, Strong and Musgrave, Glaessner248 and others. Sievers found B. coli very common in Finland.
In the majority of the cases described by Sievers from Finland, and in other cases from Central Europe, the patients suffered from obstinate intestinal catarrh, which did not always cease even after the Balantidia had disappeared. On the other hand, Balantidia have occasionally still been found to persist, though in small numbers, after the catarrh has been cured. Some authors, nevertheless, do not
Since Leuckart confirmed the frequent presence of B. coli in the rectum of pigs, and corresponding observations were made in other countries, the pig is universally considered to be the means of the transmission of Balantidium to man. The encysted stages only serve for transmission, because, according to all observations, the free parasites have a very small power of resistance. They perish when the fÆces have become cool; they cannot live in ordinary, slimy, or salt water. As they are killed by acids even when much diluted, they cannot pass through the normal stomach alive except under the most unusual circumstances. The pigs, in whose intestines the Balantidium appears to cause little or no disturbance, evacuate numerous encysted Balantidia with the fÆces, and their occasional transference to man brings about their colonization there, but perhaps only when a disease of the colon already exists.
Experimental transmission of the free parasites to animals (per os or per anum) yielded negative results, even in the case of pigs. Casagrandi and Barbagallo (1896), however, had positive, as well as negative, results. They employed healthy young cats, or cats in which catarrhal entero-colitis had been artificially induced (which in other experiments is apt to cause the death of the animals experimented upon in about six or seven days), or finally cats that had dilatation of the rectum with alkaline reaction of the fÆces. An attempt to infect three healthy cats by injecting human fÆces containing Balantidium into the rectum proved negative, in so far as the fÆces of the experimental animals had an acid reaction and contained no Balantidia, but at the autopsy performed eight days after infection a few encysted parasites were found in the mucus of the ileum. In the case of four cats
More recent experiments by Brumpt have shown that young sucking pigs can be infected with Balantidium from infected monkeys (Macacus cynomolgus) and suffer heavily from the same, whereas the Balantidium of the pig is rarely harmful to its host. This and previous experiments may be thought to suggest that there are perhaps several pathogenic species, and also that harmless strains of Balantidium may occur. At the same time, it must be remembered that a large proportion of the cases recorded of Balantidian colitis occur among swineherds and butchers, that is, among people in frequent contact with pigs. Morphologically, there are practically no differences between the Balantidia found in man, monkeys and pigs, and it is probable that one species only, under slightly different environmental conditions, may be responsible for the colitis observed. In any case, efficient prophylactic measures should be taken against balantidiasis in countries where it may occur, by confining the pigs and not allowing them to run in yards and dwellings.
E.L. Walker (1913) has given a good summary of work on balantidiasis. His own researches in the Philippines showed that monkeys could be infected by Balantidia both from pigs and men. Parasites may appear in the stools only at infrequent intervals. He
Behrenroth (1913) has given an interesting account of Balantidium coli and its pathogenic significance.
Balantidium minutum, Schaudinn, 1899.
Fig. 115.—Balantidium minutum. P, peristome; N, nucleus; M, micronucleus; V, contractile vacuole. Food vacuoles are represented in the endoplasm. (After Schaudinn.)
The body is of oval form, with the anterior extremity pointed, and posterior extremity broad and rounded (fig.115). The length is 20µ to 32µ, and the breadth is 14µ to 20µ. The peristome, which is fissure-like, extends to the centre of the body (fig.115). The right lateral border of the peristome is beset with cilia the same length as those of the body, the left side terminates in a thin hyaline membrane that extends towards the back, and can pass over to the right side. A row of longer and stronger cilia (cirri) are on the left border of the peristome. The cuticle is refractile, the ectoplasm hyaline and the endoplasm granular, with numerous food vacuoles.
A single contractile vacuole lies dorsally and to one side at the posterior extremity. The macronucleus, which is always spherical, is central and is 6µ to 7µ in diameter. The micronucleus, close in front of it, only measures 1µ (fig.115). The cysts are oval.
These parasites were found in numbers in the evacuations of a man aged 30, who was born in Germany and had repeatedly travelled between Hamburg and North America, where he made long stays. The patient came to the CharitÉ in Berlin to seek advice for constipation alternating with diarrhoea accompanied by abdominal pain.
A second case (the parasite of which was described as Colpoda cucullus by Schulz) was observed in a patient in the same institution.
As, in both cases, the parasites only appeared during the diarrhoea, and disappeared as soon as the fÆces had assumed a normal consistency, or could only be demonstrated in a few encysted specimens, it may be assumed that the small intestine or the duodenum is their habitat.
Genus. Nyctotherus, Leidy, 1849.
Flat, heterotrichous Infusoria, kidney- or bean-shaped. The peristome commences at the anterior pole of the body and extends along the concave side to the
Nyctotherus faba, Schaudinn, 1899.
Fig. 116.—Nyctotherus faba. P, peristome; N, nucleus; M, micronucleus; V, contractile vacuole. (After Schaudinn.)
The body is bean-shaped, and a little flattened dorso-ventrally. It is 26µ to 28µ long, 16µ to 18µ broad, and 10µ to 12µ thick (fig.116). The peristome is on the right border and extends to the middle; at the left there are large adoral cilia, the cilia on the right border not being larger than those on the body. The cytopharynx is short, slightly curved and turned backwards. The contractile vacuole is large, spherical, situated at the posterior extremity, and its contents are voided through the anus at its left. The macronucleus is in the centre of the body; it is globular (6µ to 7µ in size), and contains four or five chromatin masses. The micronucleus lies close to it, and is spherical or somewhat elongate measuring 1µ to 1·5µ (fig.116). The cysts are oval.
This species has hitherto only been seen once in the same patient in whom Balantidium minutum was discovered.
Nyctotherus giganteus, P. Krause, 1906.
Under the name Balantidium giganteum n. sp., P. Krause described an Infusorian which was repeatedly observed with Trichomonas intestinalis in the alkaline evacuations of a typhoid patient in Breslau. The body is ovoid, narrower and rounded anteriorly and broader and stunted posteriorly. The peristome lies to one side; the macronucleus is bean-shaped, the micronucleus small and globular; one or two vacuoles are present. The anus is at the farther end. The organism is 90µ to 400µ long, 60µ to 150µ broad (fig.117). After a prolonged stay outside the body, it becomes rounded and encystment occurs. In the thermostat the Infusoria remain alive at 37°C. for five weeks.
The species, however, hardly belongs to Balantidium, but to all appearances is a Nyctotherus and is distinguished from N. faba by the difference in size.
[Nyctotherus] africanus, Castellani, 1905.
In the fÆces of a native of Uganda who suffered from sleeping sickness and diarrhoea and had in his intestine Ascaris lumbricoides, Trichocephalus trichiurus and Ancylostoma duodenale, Castellani found a curiously shaped Infusorian, 40µ to 50µ long, and 35µ to 40µ broad, with spherical macro- and micronucleus and a contractile vacuole (fig.118). He included the organism in the genus Nyctotherus, perhaps wrongly, or the parasite may have been deformed. After the patient’s death the same parasite was found in the intestine and especially in the cÆcum.
Fig. 117.—Nyctotherus giganteus. (After Krause.)
Fig. 118.—Nyctotherus africanus. (After Castellani.)
G. Lindner, in Cassel, studied certain peritrichal Infusoria (stalkless Vorticella), and connected them, probably incorrectly, with the most varied diseases of man and domestic animals, even with Sarcosporidia of pigs. It may be mentioned that according to a communication by letter from Schaudinn, Vorticella may be found in freshly evacuated fÆces, but always only after the administration of a water enema. In spite of this, several other investigators mention VorticellÆ as intestinal parasites of man.
The Chilodon dentatus (Ehrenberg) recorded in 1903 by J. Guiart as a parasite of man, which may be found in all infusions, can hardly have lived in the man from whose fÆces it was cultivated, but may represent a chance admixture both in the fÆces and the cultivations. C. uncinatus was also found as a chance parasite of man by Manson and Sambon. According to Doflein250 (1911) certain Chilodon-like organisms have been found by Selenew in prostate secretions in gonorrhoea. Other species of the genus Chilodon are known, but only as ectoparasites (e.g., Chilodon cyprini, Moroff, 1902, from the skin and gills of diseased carp).
A number of other parasitic Ciliates are known, among which Ichthyophthirius multifiliis, destructive to fish, is important. It lives in the skin and the layers immediately below it, forming small whitish pustules which may become confluent.
Opalina ranarum, parasitic in the rectum and urinary bladder of frogs and toads, shows great degradation and simplification due to parasitism, possessing no separate micronuclei, no cytostome, cytopharynx or cytopyge. It has many macronuclei, and is a large parasite. During summer and autumn nuclear multiplication followed by division of the body occurs, the process being repeated after the daughter forms have grown to the size of their parent. In spring, the Opalina divide rapidly, but do not grow much before dividing again. Finally, tiny forms, containing three to six nuclei, encyst and pass from the host with the fÆces. As these latter are greedily devoured by tadpoles, the Opalina gain new hosts in which they develop.
THE CHLAMYDOZOA.
The name Chlamydozoa was proposed by Prowazek in 1907 for a number of minute, problematic organisms (fig.119) believed to be the causal agents of certain diseases in man and animals, such as vaccinia and variola, trachoma, inclusion blenorrhoea in infants, molluscum contagiosum, and bird epithelioma contagiosum. Other diseases possibly due to Chlamydozoa251 are hydrophobia, measles, scarlet fever, foot-and-mouth disease, the “Gelbsucht” disease of silkworms, and perhaps even typhus (Prowazek, 1913). The subject is difficult and controversial and can only be briefly discussed here. It is known that the viruses in all these diseases can pass through ordinary bacterial filters, that is, they belong to the group of “filterable viruses.” At such periods the organisms are extracellular or free. It is also known that in many of these cases the virus produces definite and characteristic reaction-products or cell-inclusions in the infected cells, during the intracellular phase of the life-history of the organism. As the organisms to be considered are problematic, it will be convenient to summarize their history:—
(1) Cell-inclusions, usually named after their discoverers, have been found in certain diseases, thus: In vaccinia Guarnieri’s bodies,
(2) At first these characteristic cell-inclusions were considered to be actual parasitic organisms causing the diseases in question. The bodies received zoological names and attempts were made to work out their supposed development cycles. The supposed parasites of vaccinia and variola were referred to a so-called genus Cytoryctes, those of hydrophobia to Neuroryctes, of scarlet fever to Cyclasterium, while those of molluscum contagiosum were referred to the Coccidia. Calkins in 1904 studied in detail the cell-inclusions of vaccinia and small-pox, calling them Cytoryctes variolÆ, Guarnieri. Calkins considered that in the stratified cells of the epidermis they passed through two cycles, the one cytoplasmic, the other intranuclear. The first is the vaccinia cycle, the second the pathogenic (intranuclear) variola cycle. It is hardly necessary to follow all Calkins’ stages here.
Negri (1909) described a cycle for Neuroryctes hydrophobiÆ. Calkins refers both Cytoryctes variolÆ and Neuroryctes hydrophobiÆ to the Rhizopoda.
Siegel (1905) described quite different organisms under the name Cytorhyctes. He listed several species: C. vacciniÆ; of vaccinia and small-pox, C. scarlatinÆ of scarlet fever, C. luis of syphilis (this is probably the granule stage of Treponema pallidum), and C. aphtharum of foot-and-mouth disease.
(3) The afore-mentioned views were criticized, and the bodies were not considered to be living organisms but merely reaction products or cell-inclusions due to the effects of the virus on the host cells. Thus Guarnieri’s bodies were stated to consist of extruded nucleolar or plastin material, having no developmental cycle. It was further asserted that infection could be produced by lymph in which Guarnieri’s bodies had been destroyed. Similar assertions have been made regarding the Negri bodies, and others. The Cytoryctes, Neuroryctes, etc., are considered, according to these views, to be degeneration products of the nucleus or to be of a mucoid nature.
(4) More recently a positive belief has gained ground that there are true parasitic organisms causing these diseases, and that the parasites are very minute, being termed Chlamydozoa by Prowazek and Strongyloplasmata by LipschÜtz.
The Chlamydozoa are characterized by (a) their very minute size, smaller than any bacteria, so that they can pass through bacterial filters; (b) they pass through intracellular stages, in the cytoplasm or the nucleus of the host cell, producing therein the reaction products or inclusions in the cell already recorded as characteristic or diagnostic of the diseases produced; (c) they pass through definite developmental cycles. Such a cycle consists essentially of growth
The Chlamydozoa are parasites of epiblastic tissues (e.g., epidermal cells, nerve cells, conjunctival cells).
Fig. 119.—Chlamydozoa. Trachoma bodies in infected epithelial cells of the conjunctiva. (a) initial bodies (above) and cluster of elementary bodies (touching the nucleus); (b) cluster of granules surrounded by mantles. ×2,000 approx. (Original. From preparation by Fantham.)
The life-history of a ChlamydozoÖn (fig.119), such as that of vaccinia, is, according to Prowazek, Hartmann and their school, as follows:—
1. The infection begins with elementary bodies or elementary corpuscles which live at first extracellularly. An elementary body is a minute speck of chromatin, apparently devoid of cytoplasm, which can pass through a bacterial filter. It can enter a host cell, but the entry is not a process of phagocytosis.
2. Inside the host cell the elementary body grows in size, and becomes an initial body (fig.119, a).
3. A reaction on the part of the host cell results, for nucleolar, plastin substance is extruded from the cell-nucleus and surrounds the parasitic initial body. The latter is thus enveloped in a mantle (hence the name Chlamydozoa, from ??a??, a mantle), and the characteristic cell-inclusion (Guarnieri’s body, Negri’s body, etc.) is produced. The nucleolar, mantle substance probably represents the “cytoplasm” of Cytoryctes, described by Calkins.
4. The body next breaks up into a number of smaller bodies known as initial corpuscles. These, in their turn, divide by simple division (in the manner already described) into numerous elementary bodies (fig.119). Thus, the life-cycle is completed.
The Chlamydozoa are, then, the minute granules inside the body of the Cytoryctes variolÆ or the Neuroryctes hydrophobiÆ, so that the whole body of the Cytoryctes or Neuroryctes corresponds to the mantle and parasite of the ChlamydozoÖn. The Cytoryctes group is said to cause destruction of the host cell. The CytoÖikon group (e.g., trachoma bodies) causes proliferation of the host cell.
In September, 1913, Noguchi252 described the cultivation of the parasite of rabies in an artificial medium, similar to that used by him for the cultivation of SpirochÆta recurrentis. The cultures were stated to be infective to dogs, rabbits and guinea-pigs. Levaditi, in December, 1913, stated that he had succeeded in cultivating spinal ganglia of rabid monkeys in monkey plasma.
Noguchi and Cohen (November, 1913)253 have succeeded in cultivating the so-called trachoma bodies, or at any rate bodies very closely resembling them morphologically. The medium employed was Noguchi’s ascitic fluid and rabbit kidney medium, as used for spirochÆtes. The coarser cultural forms stained blue with Giemsa’s solution, the finer ones stained red. Attempts to infect monkeys from the culture tubes failed.
From their behaviour on treatment with such reagents as saponin, bile and sodium taurocholate, Prowazek considers that the Chlamydozoa approach the Protozoa.
PROTOZOA INCERTÆ SEDIS.
Sergentella hominis, Brumpt, 1910.
Et. and Ed. Sergent in 1908 found vermiform bodies about 40µ long by 1µ to 1·5µ broad in the blood of an Algerian suffering from nausea and cold sweats, without other symptoms. The bodies were pointed at each end, with a somewhat ill-defined nucleus in the middle. Their systematic position is doubtful.
Note.—An Appendix on Protozoology will be found on pp.733–752. This has been prepared in order to incorporate a number of new additions to knowledge made since the body of the book was printed off.
B. PLATYHELMINTHES, or Flat Worms.
BY
J.W.W. STEPHENS, M.D., B.C., D.P.H.
Definition: Bilaterally symmetrical animals without limbs, the form of which is leaf or tape-like, rarely cylindrical, and whose primary body cavity (segmentation cavity) is absent, the cavity being filled by a mesenchymatous tissue (parenchyma).
The mouth is either situated at the anterior end of the body, or is shifted more or less backwards on to the flat ventral surface. The alimentary canal consists of a short fore-gut, which is frequently provided with a muscular pharynx, and of a simple forked or branched mid-gut; there is neither a hind-gut nor an anus; in one class, the Cestodes, the alimentary canal has entirely disappeared except for muscular remnants in the scolex.
The INTEGUMENT OF THE BODY consists either of a ciliated epithelium of only one layer (Turbellaria), or of a cuticle and gland-like cells embedded in the parenchyma, or subcuticular layer (Cestodes, Trematodes). The dermo-muscular layer consists of annular, longitudinal, and even diagonal fibres, while the parenchyma is traversed by dorso-ventral fibres.
The central NERVOUS SYSTEM, which is embedded in the parenchyma of the body, consists of cerebral ganglia, united together in the shape of dumb-bells, and of two or more longitudinal MEDULLARY FASCICLES, often forming transverse anastomoses. Organs of sense usually occur only in the free-living species, more rarely during the free-living stages of a few parasitic species and in a few ectoparasitic forms.
[In Platyhelminthes simple eye-spots frequently occur, and in a few an auditory vesicle.]
Blood-vessels and definite RESPIRATORY ORGANS are lacking [except in Nemertinea]; the EXCRETORY APPARATUS (formerly termed water-vascular system) is typical of the entire class. It commences in the interstices of the parenchyma, with peculiar terminal cells (ciliated funnels), which will be described later (p.219), the capillary processes of which go on uniting into larger branches, and finally form two large collecting vessels, which, sometimes separately and sometimes united, open to the exterior through one, two, or numerous pores.
Nearly all the Platyhelminthes are HERMAPHRODITIC, and in nearly all there are, in addition to the ovaries producing ova, other glands attached to the female genital apparatus, namely, the vitellaria or yolk glands, which provide a substance termed yolk, which serves as nourishment for the embryo. The fully formed eggs have shells and are “compound,” i.e., composed of the egg or ovarian cell, which is surrounded by numerous yolk cells or their products of disintegration. The two sexual openings usually lie close together, frequently in the fundus of a genital atrium; they are rarely separated from one another. Shell glands also usually occur (p.221).
Reproduction is sexual, often, however, combined with asexual methods of propagation (segmentation, budding). The Platyhelminthes live partly free in fresh or salt water, exceptionally also on land. The greater part, however, live as parasites on or in animals.
Classification of the Platyhelminthes.
Class I.—Turbellaria (or Eddy Worms). Flat worms for the most part, free living, and always covered with a ciliated epithelium.
Order 1.—Rhabdocoelida, gut unbranched.
Order 2.—Tricladida, gut with three main branches.
Order 3.—Polycladida, a central gut with lateral cÆca. Development direct or through metamorphosis. They live in fresh and salt water or on land; very seldom as parasites.
Class II.—Trematoda (Sucking Worms254). [Usually known as Flukes.—F.V.T.] Flat worms, living as ecto- or endoparasites, that are only ciliated in the larval condition, and in their adult state are covered with a cuticle, the matrix cells of which lie in the parenchyma. They have either one, a few, or several suckers,255 and frequently also possess chitinous fixation and adhesive organs. The intestine is single, but generally bifurcated, and not uncommonly there are transverse anastomoses between the forks or diverticula on them. Excretory organs double, with two orifices at the anterior extremity or a single one at the posterior end. Development takes place by a metamorphosis or alternation of generations (p.283). These worms are almost always hermaphroditic, with two or more female and one male sexual orifice. They live, almost without exception, as parasites on vertebrate animals, but the intermediate generations are passed in molluscs.
Class III.—Cestoda (Tapeworms). Endoparasitic flat worms without an alimentary canal. The larval stages are rarely ciliated, but are usually provided with six spines; the adult worm is covered with a cuticle, the matrix cells of which are embedded in the parenchyma. The body consists of a single segment (Cestodaria) or a chain of segments, in which case it consists of the scolex and the segments containing the sexual organs (proglottides) (Cestodes s. str.). The scolex is provided with various adhesive and fixation organs, and there are calcareous corpuscles in the parenchyma. Excretory organs symmetrical, opening at the posterior end. These worms are always hermaphroditic, and then possess one or two female and one male sexual orifice. During development a larval intermediate stage (“measle”) occurs and almost always in a different host to that in which the adult sexual worm lives. The adult stage is parasitic in vertebrate animals; but the larval stage may occur in invertebrates.
Class II. TREMATODA, Rud.
These worms are usually leaf- or tongue-shaped, but also barrel-shaped or conical; they vary from 0·1mm. to almost 1m.256 in length; most of them, however, are small (5mm. to15mm.). The surface on which the orifice of the uterus and the male sexual opening are situated is termed the ventral surface; the oral aperture, which also acts as anus, is always at the anterior end in the sub-order Prostomata (p.230), but in the sub-order Gasterostomata it is ventral.
Suckers are always present and occur in varying numbers and positions at the anterior extremities as well as on the ventral surface, and occasionally on the lateral margin and on the dorsum; the beginning of the intestine (mouth) is always surrounded by a sucker in the Prostomata.
In or near the suckers there may be chitinous hooks, claws or claspers, or the surface of the body is more or less covered with spines, scales or prickles; in one genus (Rhopalias) there are projectile tentacles beset with spines on the sides of the anterior part of the body.
The body of adult Trematodes is covered by a homogeneous layer of varying thickness, which either lies directly over the external layer (basement membrane) of the parenchyma, or over the muscles embedded in the parenchyma. This investing membrane (cuticle) arises from pear-shaped or spindle-shaped cells arranged singly or in groups (which lie between or internal to the diagonal muscles), and is connected with them by processes; these cells one may regard as epithelial cells which have sunk down, or possibly as parenchymatous cells. An epithelium of one layer is also found on the body of young stages, but it disappears during growth, and only occasionally do its nuclei persist until adult life. In its place we then find the cuticle, which, moreover, extends into all the body openings more or less deeply.
It is thus a debatable point whether the “investing layer” of flukes is a cuticle—that is, consists of modified epithelial cells—or whether it is a basement membrane, i.e., compressed and modified connective tissue cells; in this latter case the true epidermis and cuticle have been cast off. In the former case the epidermal cells are the pear-shaped cells referred to above. According to recent authors it consists of two parts, an outer true cuticle and an inner basement membrane. There are also unicellular cuticular glands, lying isolated or in groups, which are termed cephalic, abdominal, or dorsal glands according to the position of their orifice.
The PARENCHYMA is a connective substance, the structure of which is still a matter of dispute. It consists, according to some authors, of multipolar cells, the offshoots from which anastomose with each other so that a network, permeating the entire body and encompassing all the organs, is produced. There exists also, as part of it, a homogeneous matrix, in the form of lamellÆ and trabeculÆ that border small cavities communicating with each other and filled with fluid. According to other authors, the parenchyma of the Trematodes consisted originally of cells, of which, however, only the cell membranes remain, while the protoplasm has been liquefied except for small residua around the nucleus. Between these cells an intercellular mass has appeared. By partial absorption of the walls, adjoining spaces unite,
The MUSCULAR SYSTEM of the Trematodes is composed of (1) a dermo-muscular tube, (2) the dorso-ventral or parenchymal muscles, (3) the suckers, and (4) the special muscles of certain organs.
The dermo-muscular tube, which lies fairly close to the cuticle, consists of annular, diagonal, and longitudinal fibres which surround the entire body in one or several layers, and as a rule are more strongly developed on the ventral surface as well as in the anterior part of the body. The MUSCLES OF THE PARENCHYMA are found chiefly in the lateral parts of the body and pass through the parenchyma in a dorso-ventral direction; their diverging brush-like ends are inserted on the inner surface of the cuticle (fig.120).
Fig. 120.—Half of a transverse section through Fasciola hepatica, L. 25/1. Cu., Cuticle with scales; under the cuticle are circular muscles, and adjoining them the longitudinal and diagonal muscles; internal to the latter are the matrix cells of the cuticle; I., gut; the other similarly contoured cavities are gut diverticula that have been transversely or obliquely sectioned; F.v.s., vitellaria; Ex.v., excretory vessels; T., testes; Md., median plane; the fibres passing from the ventral to the dorsal surface are the muscles of the parenchyma. The parenchyma itself is omitted.
The suckers are specially differentiated parts of the dermo-muscular tube. Their concave inner surface is lined by the continuation of the cuticle and their convex external surface is covered by a more dense tissue that frequently takes the form of a refractive membrane, thus separating them from the parenchymal muscles.
The principal mass of the suckers consists of muscular fibres which run in three directions—equatorial, meridional and radial. The equatorial fibres correspond to the annular muscles, the meridional fibres to the longitudinal muscles, and the radial fibres to the muscles of the parenchyma; the radial fibres are always the most strongly
Fig. 121.—Harmostomum leptostomum, Olss., an immature specimen from Helix hortensis. Nervous system, according to Bettendorf. A.s., ventral sucker; C.g., cerebral ganglion; Ex.p., excretory pore; G.p., genital pore; O.s., oral sucker; M.d., dorsal medullary nerve; M.l., lateral medullary nerve; N.ph., pharyngeal nerve; M.v., ventral medullary nerve. Magnified.
Of the muscles of the organs which have developed from the parenchyma muscles we may briefly mention those bundles that are attached to certain parts of the genital apparatus, to the suckers, to the hooks and claws, and also, at all events in Fasciola hepatica, to the spines. The sheaths used for the projection of the tentacles of the RhopaliadÆ are also muscular.
The contractile elements consist of fibres of various lengths that are mostly parallel to one another, and frequently anastomose; a cortical substance finely fibrillated can usually be distinguished from an internal homogeneous mass; large nucleated cells of uniform size are always connected with them; these have been variously interpreted, but have been proved to be myoblasts, one or more of their processes constituting the muscular fibres.
The MOVEMENTS of the Trematodes consist in alterations of form and position of the body, as well as in creeping movements.
In the NERVOUS SYSTEM (fig.121) can be distinguished a cerebral portion as well as strands (medullary strands) running from it, and peripheral nerves. The cerebral portion always consists of two large ganglia situated in the anterior end of the body which pass dorsally over the oesophagus and are connected by means of a broad and thick commissure composed of fibres only. From each ganglion three nerves run anteriorly—the inner and dorsal nerve for supplying the anterior dorsal part of the body; the median and ventral for the oral sucker; and the exterior and lateral likewise for the supply of the sucker.
In a similar manner three strands run backwards from each ganglion—one dorsal, one lateral and one ventral. The dorsal and ventral strands become united and curve backwards; the symmetrical lateral strands are connected by means of transverse commissures, the number of which vary according to the species. Such commissures also exist between the lateral and the two other strands on each side. There are ganglion cells along the entire course of the posterior cords, more particularly at the points of origin of the commissures. There also appears to be in addition a fourth anterior and posterior pair of nerves, the front pair for the oral sucker and the hind pair for the pharynx.
The peripheral nerves, which spring from the posterior strands as well as from the commissures, either pass directly to the muscular fibres or to the sensory cells that are situated at the level of the subcuticular cells, or they reach these after the formation of a plexus situated immediately beneath the dermo-muscular layer; the processes directed outwards terminate in small vesicles in the cuticle.
As to other ORGANS OF SENSE, simple eyes, two or four in number, are known in several ectoparasitic species as well as in a
Fig. 122.—Median section through the anterior part of Fasciola hepatica: the oral sucker, pharyngeal pouches, pharynx, oesophagus, cuticle with spines, and the body parenchyma.
The ALIMENTARY CANAL commences with an oral aperture, generally terminal or sub-terminal (ventral) at the anterior extremity, which leads into an oral cavity usually surrounded by a sucker; the oesophagus, of various lengths, is directed backwards and is generally surrounded by a muscular pharynx (fig.122). In some cases there exists between the sucker and pharynx, pharyngeal pouches (prÆpharynx). Sooner or later the intestine divides into two lateral branches directed backwards, both of which end blindly (cÆca) at the same level.257 In many ectoparasites (Monogenea [p.222]) a connection exists between the genital glands and one of the intestinal branches (ductus vitello-intestinalis [fig.123]).
The oral cavity, pharyngeal pouches, pharynx, and oesophagus are lined with a continuation of the cuticle of the body; the gut cÆca are lined with tall cylindrical epithelium (fig.120). The oesophagus and intestinal branches often have also one layer of annular and longitudinal muscles; the pharynx has essentially the structure of a sucker (fig.122).
The accessory organs of the alimentary canal consist of groups of unicellular SALIVARY GLANDS that discharge into the oesophagus in front of or behind the pharynx, or even into the pharynx itself.
The food of the Trematodes consists of mucus, epithelial cells, the intestinal contents of the hosts, and often also of blood, and this not only in those species living in the vascular system, but also in species living as ectoparasites or in the intestine or biliary passages of their hosts.
Fig. 123.—Polystomum integerrimum, a monogenetic fluke from the urinary bladder of the frog. i., intestine; h., large hooks of the sucking disc; h.k., smaller hooklets; l.c.v., longitudinal vitelline ducts; o., oral orifice; Oot., oÖtype; ov., ovary; s.p., suckers of the disc; tr.c.v., transverse vitelline ducts; Ut., uterus with ova; v., entrance to the vagina; v.d.e., vas deferens; v.d.i., ductus vitello-intestinalis; the vitellaria and testes are not shown. Magnified. (After Zeller.)
Fig. 124.—Allocreadium isoporum, Looss. Excretory apparatus. Of the other organs, the oral sucker, pharynx, genital pore, ventral sucker, ovary and testes are shown; the cylindrical excretory bladder is in the posterior end. 38/1. (After Looss.)
The final products of assimilation dissolved in the fluids of the body are distributed throughout the parenchyma and are thence
The EXCRETORY SYSTEM258 consists of several parts: (1) of the more or less numerous terminal “flame” cells or funnel cells (figs.124, 125); (2) of the capillaries ending in them; (3) of larger vessels receiving the capillaries; and (4) of the excretory bladder. Terminal cells and capillaries may be compared to unicellular glands with long excretory ducts; the cellular body (fig.125) is comparatively large, stretched longitudinally, more rarely transversely, and provided with numerous processes, that are lost in the parenchyma; within is a conical cavity (analogous to the secretory cavity of unicellular glands) which is continued directly into the structureless capillary; at its blind end is a bunch of cilia projecting into the cavity, and which, during life, shows a flickering motion (ciliary flame). The nucleus is situated in the protoplasm of the terminal cell at its blind end.
Fig. 125.—Terminal flame cell of the excretory system. n., nucleus of cell; c., bundle of cilia forming the “flame”; p., processes of cell extending into parenchyma; d., excretory capillary. (Stephens.)
The entire apparatus thus begins blindly—i.e., within the terminal cells, to which must be ascribed the capacity of taking up from the fluid that permeates the parenchyma the products which are first collected into their own cavities and thence excreted by means of the capillaries and vessels.
The vessels possess definite walls, consisting of a membrane and a nucleated protoplasmic layer. They unite at many points on either side, and again pass into other canals (COLLECTING TUBES), which finally, travelling towards the posterior end, discharge into the excretory bladder (fig.124).
The form and size of the bladder vary much according to the different species, but it always possesses its own flattened epithelium, surrounded by circular and longitudinal muscles, the circular muscles
The contents of the entire apparatus usually consist of a clear or sometimes reddish fluid; in some species there are larger or smaller granules, and occasionally also concretions occur.
Fig. 126.—Diagram of female genitalia. Ov., ovary; ovd., oviduct; L.c., Laurer’s canal; Rec. sem., receptaculum seminis; Vit. R., vitellarian reservoir; t.v.d., transverse vitelline duct; Oo., oÖtype; Sh. gl., shell gland; Rec. ut., receptaculum uterinum; ut., uterus. (The various parts are not to the same scale.) (Stephens.)
Fig. 127.—Diagram of male and part of female genitalia. ut., uterus; vag., vagina; ?, opening of vagina; g.s., genital sinus; g.p., genital pore; ?, opening of ejaculatory duct or vas deferens; c.s., cirrus sac; c., cirrus; p.p., pars prostatica; s.v., seminal vesicle; e.j., ejaculatory duct or vas deferens; v.e., vas efferens; t., testis. (Stephens.)
Sexual Organs.—Nearly all the Trematodes are hermaphrodites, and only a few (SchistosomidÆ, Koellikeria) are sexually differentiated. The sexual organs usually lie in the “central field” limited by the gut cÆca; the vitellaria, on the other hand, are, as a rule, external to the gut cÆca in the “lateral fields.”
The male apparatus259 is composed of two variously formed testes (fig.127) (globular, oval, indented, lobed, or ramified), which may lie side by side or one behind the other; from each testicle a tube (vas efferens) originates; sooner or later, both tubes as a rule unite to form the ejaculatory duct or vas deferens, which is frequently
The female genitalia (fig.126) consist of an ovary, usually situated in front of the testes, the form of which varies according to the species, the usually double vitellaria, the ducts and a number of auxiliary organs; the short oviduct directed towards the centre arises from the ovary, and is connected in the median line with the excretory duct of the vitelline glands. These grape-like glands possess longitudinal excretory ducts, which assume a transverse direction behind the ovary, unite together at the median line and form a single duct, often dilated into a vitelline receptacle, that unites with the oviduct. Near this point, moreover, there frequently opens a canal (Laurer’s canal) which begins on the dorsal surface, and on the inner end of which a vesicle filled with sperm (receptaculum seminis) usually occurs (fig.126). Moreover, there are also numerous radial unicellular glands (shell glands) at or beyond the point of junction of the oviduct, vitelline ducts and Laurer’s canal. In this portion of the duct (oÖtype), which is usually dilated, the ovarian cells are fertilized, surrounded with yolk cells and shell material, and as ova with shells they pass into the uterus (a direct continuation of the oviduct), which, with its many convolutions, occupies a larger or smaller portion of the central field, and runs either direct to the genital pore or, forming convolutions, first runs posteriorly and then bends forward (descending and ascending limbs). In both cases the terminal part lies beside the cirrus pouch and discharges beside the male orifice either on the surface of the body or into a genital atrium. The terminal portion of the uterus, which is often of a particular structure, serves as a vagina (METRATERM).
The cirrus sac may include (1) the genital atrium (i.e., the common sinus, into which the vas deferens and vagina may open), or (2) a variable extent of the vas from cirrus to seminal vesicle. Thus the latter may be outside the sac. In the absence of a sac, the genital sinus may be surrounded by a pseudo-sucker, as in Heterophyes (in some cases the ventral sucker itself, from its close proximity to the genital pore, serves as an accessory copulatory organ). In other cases
The GENITAL PORE, which is the opening from the genital sinus on to the surface, is generally situated at or near to the median line on the ventral surface and in the anterior region of the body; in most of the Distomata it is in front of the ventral sucker, in other cases, e.g., in the CryptocotylinÆ, it is behind.260
The spermatozoa do not differ essentially in their structure from those of other animals; the ovarian or egg cells are cells without integument and contain a large nucleus and a little protoplasm; the vitellaria also produce nucleated cells, in the plasm of which there are numerous yellow yolk granules; the yolk cells detach themselves, like the ovarian cells, from the ovarium, and pass into the oviduct to surround each ovarian cell in the oÖtype. They disintegrate sooner or later in the completely formed egg and are utilized as food by the developing embryo.
Development of the Trematodes.
(1) Copulation.—Observation has demonstrated that the one or two vaginÆ occurring in the ectoparasitic Trematodes are utilized as female organs of copulation, and that the copulation is cross; it is also known that Laurer’s canal, which was formerly generally regarded as the vagina, has only quite exceptionally, if at all, served the digenetic Trematodes as such—it appears to be homologous with the canalis vitello-intestinalis of the Monogenea261—but the terminal portion of the uterus, termed the metraterm, is used for copulation. Cross-copulation occurs as well as auto-copulation and auto-fecundation. The spermatozoa subsequently pass through the entire uterus, which is still quite short at the time the male organs are matured; the maturation of which, as usually is the case in hermaphrodites, precedes
Fig. 128.—Ovum of Fasciola hepatica, L., cut longitudinally. The lid has been lifted in the process. Within the egg are numerous yolk cells, and at the lid end there is the still unsegmented ovum (dark). 240/1.
Fig. 129.—Miracidium of Fasciola hepatica that has just hatched from the egg, with a distinct cuticular ciliated epithelium. Magnified. (From Leuckart.)
(2) Formation of the Ova.—The ovarian cells arising from the ovary first become mature after their entry into the oÖtype by the formation of three polar bodies, fertilization then taking place. At the same time as the ovarian cell a number of yolk cells from the vitellarium and secretion, drop by drop, from the shell gland reach the oÖtype.262 The shell is then formed during the generally active contractions of the oÖtype walls and then passes on into the uterus. In the uterus of the endoparasitic trematodes the eggs accumulate more and more, often in large quantities, while in ectoparasitic species generally only one or some few eggs can be found. The completed ova are of various forms and sizes. They are mostly oval, at all events in the digenetic trematodes, and the yellowish or brown shell is provided with an opening at one pole which is closed by a watch-glass-shaped lid (operculum). Appendages (filaments) on the shell—at one or both poles—are uncommon, but are the rule in the ova of the Monogenea (ectoparasitic species).
(3) Deposition of the Ova.—Soon after their formation, the Monogenea (ectoparasitic trematodes) deposit round the place of
(4) The embryonic development, after irregular segmentation of the ovum into a number of blastomeres, leads to the formation of a solid blastosphere or morula, which is surrounded by a cellular investing membrane (yolk envelope), while the principal mass of the cells forms the embryo, which uses for its nourishment the yolk cells, which have in the meantime disintegrated (cf. footnote, p.223). Usually, after the ova have reached water the embryos hatch out, leaving the yolk envelope in the egg-shell; in other cases, however, the embryos only hatch out after having been subjected to the influence of the intestinal juices, that is to say, in the intestine of an intermediate host which has ingested with its food the ova that have escaped from the primary host.
(5) The post-embryonic development of the Trematodes is accomplished in various ways; the process is the most simple in the ectoparasitic species (Monogenea), the young of which should certainly be regarded as larvÆ, because they possess characteristics (cilia, simple gut, etc.) that are lacking in the adult worms, but which, nevertheless, pass into the adult state direct after a relatively simple metamorphosis. In the Holostomata,263 a group found chiefly in the intestine of aquatic birds, and which rarely occur in other vertebrates, the ova develop in water. The young are ciliated all over, and, after having entered an intermediate host (leeches, molluscs, arthropods, amphibians, fishes) living in the water, they undergo a metamorphosis into a second larval stage; they then encyst and await transmission into the final host, where they become adult Metastatic trematodes, i.e., trematodes without asexually produced generations (p.229).
Fig. 130.—A group of cercariÆ of Echinostoma sp. (from fresh water). 25/1.
In the remaining so-called digenetic trematodes (p.230) one or two asexual generations interpose between the miracidium and terminal stage, so that quite a number of adult worms may originate from one egg. Usually the young, which are termed MIRACIDIA264 (fig.129),
Accordingly the following conditions are necessary for the completion of the entire development: (1) The terminal host in which the adult stage lives; (2) an intermediate host into which the miracidia penetrate and in which they become sporocysts; (3) a second intermediate host in which the cercariÆ become encysted. In certain species, as in Fasciola hepatica, this second host is omitted, as the cercariÆ spontaneously encyst on plants, or again (in other species) encystment may occur within the first intermediate host, when,
Animals that harbour adult digenetic Trematodes thus become infected by ingesting encysted cercariÆ, which either occur (1) in certain animals (second intermediate hosts) on which they feed, or (2) in water, or (3) on plants, or finally (4) in the first intermediate host; whereas animals harbouring encysted cercariÆ have been directly infected by the corresponding tailed stage, and animals harbouring germinal tubes (sporocysts or rediÆ) have been infected by the miracidia.
Fig. 131.—Development of Fasciola hepatica, L. a, the miracidium in optical section showing cephalic lobe, x-shaped eye-spot resting on the cerebral ganglion, two germ balls; below each of these a flame cell, and still lower germ cells lying in a cavity (primitive body cavity). b, young sporocyst with two eye-spots, and germ balls; the cells lining the cavity are not shown. c, older sporocyst with a young redia. Magnified. (After Leuckart.)
Thus certain species of ducks and geese become infected with Echinostoma echinatum by devouring certain water-snails (LimnÆus, Paludina) in which the encysted cercariÆ occur. Oxen become infected with Paramphistomum cervi (= Amphistomum conicum) by swallowing with water, cysts of this species which occur at the bottom of puddles and pits. Sheep are infected with Fasciola hepatica by eating grass to which the encysted cercariÆ of the liver-fluke are attached; our song-birds infect themselves or their young with Urogonimus macrostomus by tearing off pieces containing the corresponding sporocysts which are full of encysted cercariÆ from snails (Succinea amphibia), which act as the first intermediate hosts, and eating, or offering their young these pieces.
(1) The MIRACIDIA of the digenetic Trematodes are comparatively highly organized, and the mode of their formation from the
[The germ cells of the miracidium and the germ balls of the sporocyst arise, according to some observers, by further division of undifferentiated blastomeres; according to others from the cells of the lining wall of its body cavity. It is from these free germ balls that the redia stage is developed.
[In the germ ball or morula appears an invagination, giving rise to the cup-shaped gastrula stage. This elongates and forms the REDIA (fig.131, c).
[In the interior of the redia cells are budded off and develop into gastrulÆ, as in the case of the sporocyst. These become a fresh generation of rediÆ or give rise to the third stage (CERCARIA).]
Fig. 132.—Young redia of Fasciola hepatica, with pharynx and intestine, with a circular ridge anteriorly and a pair of processes posteriorly and masses of cells (germ balls) in the interior. Magnified. (From Leuckart.)
Fig. 133.—Older redia of Distoma echinatum, with rudimentary intestine i.; cercariÆ, c.; germ balls, b.; and birth pore, g. Magnified.
(2) The SPOROCYSTS, on the contrary, which are produced direct from the miracidia, are very simple, as all the organs of the latter disappear, even to the muscles and excretory organs, during or after penetration into the intermediate host, whereas the budded and still budding cells of the wall of the (primary) body cavity continue to develop rapidly and form germ balls. The sporocysts when fully developed have the appearance of tubes or fusiform bodies with rounded edge; they are frequently of a yellow colour. Their length
(3) The REDIÆ (figs.132, 133), on the other hand, are more cylindrical and always have a simple intestine of varying length, provided with a pharynx; they likewise possess, situated near the circular ridge, a “birth pore” which serves for the exit of the cercariÆ originating within them.
Fig. 134.—Cercaria of Fasciola hepatica; the cutaneous glands at the side of the anterior body. Magnified. (After Leuckart.)
(4) The CERCARIÆ266 are very different; typically they consist of the anterior body and the oar-like tail at the posterior end (fig.134). The former, even to the genitalia, has the organization of the adult digenetic Trematodes, and thus allows the easy recognition of at least the characters of that large group to which the species in question belongs. On the other hand, however, there are also organs that are lacking in the adult form, such as, in many, the boring spine in the oral sucker, or the eyes situated on the cerebral ganglion; moreover, also, cutaneous glands (fig.134), the secretion of which forms the cyst membrane. The oar-like tail may be long or short (stumpy-tailed cercaria) or entirely absent; its free end may be partly split (furcate cercaria), or split to its base (bucephalus); in various forms also the anterior end of the tail is hollow, and has enclosed within it the anterior body, which is otherwise free. The size also of the cercaria belonging to the different species is very diverse; in addition to forms swimming in the water that have the appearance of minute milky-white bodies, there are forms which measure as much as 6mm. in length.
Fig. 135.—Encysted cercaria of Fasciola hepatica. Magnified. (After Leuckart.)
The encysted cercariÆ (fig.135) are globular or oval, and are surrounded by a homogeneous
The cycle of development of the digenetic Trematodes has hitherto been generally explained as a typical ALTERNATION OF GENERATIONS, one sexual generation regularly alternating with one or two asexually reproducing generations. Recent authors, however, regard the cells in the sporocysts from which rediÆ or eventually cercariÆ arise as parthenogenetically developing ova, and the sporocysts as well as the rediÆ as generations propagating parthenogenetically. In this case, however, it is an alternation of a sexual not with an asexual but with firstly a parthenogenetic generation (the sporocyst), the central cells of which are regarded as ova which develop parthenogenetically into the redia, and this the second parthenogenetic generation finally produces larvÆ (cercariÆ) capable of developing into the sexually mature form.
Other authors, again, regard the development of the Digenea as only a complicated metamorphosis (p.283), which is distributed over several generations before it is concluded.
Biology.
Endoparasitic Trematodes, as fully developed organisms, occur in vertebrate animals only, with very few exceptions; they inhabit almost all the organs (with the exception of the nervous and osseous systems and the male genitalia), but by preference the intestine in all its extent from the oral cavity to the anus; and, further, certain species or groups inhabit only quite restricted parts of the intestine. Besides in the intestine other species live in the liver, or in the bile-ducts, or in the gall-bladder; other accessory organs of the intestine, such as the pancreas, bursa Fabricii (of birds), are only infected by a few species. Many inhabit the lungs, or the air sacs in fowls, a few the trachea. Trematodes have also been known to occur in the urinary bladder, the urethra and the kidneys of all classes of vertebrates; they are also present in the vascular system of a few tortoises, birds and mammals; in birds they even penetrate from the cloaca into the oviducts, and are occasionally found enclosed in the laid eggs; one species is known to occur in the cavum tympani and in the Eustachian tube of a mammal (Dugong), another in the frontal sinus of the polecat; several species infest the
Trematodes live free and active within the organs attacked, though they may attach themselves by suction for a longer or shorter period; in other cases, however, they bore more or less deeply into the intestinal wall with their anterior end, or lie in cysts of the intestinal wall which only communicate with the lumen through a small opening; in those species living in the lungs of mammals the host likewise produces a cyst, which usually encloses two specimens; such association of a pair is also observed in other situations, and, though this is the rule in species sexually distinct, it is not entirely confined to these.
As regards the AGE attained by endoparasitic Trematodes, there are but few reliable records, and these differ considerably; the overwhelming majority of species certainly live about a year, or perhaps a little longer, but there are some whose term of life extends to several or many years.
Trematodes are but rarely found encysted in the higher vertebrate animals; the condition, however, is more frequent in amphibians, and especially in fishes, as well as in numerous invertebrate animals.
Classification of the Trematodes of Man.
The following classification, partly artificial, partly natural, embraces only the flukes found in man:—
Order. Digenea, v. Beneden, 1858.
Anterior sucker single and median, present. Eggs few. The (specialized) terminal portion of the uterus serves as a vagina. Development indirect, i.e., an intermediate host is required.
Sub-order. Prostomata, Odhner, 1905.
Mouth surrounded by the anterior sucker.
Group. Amphistomata, Rudolphi, 1801, ep., Nitzsch, 1819.
Gut forked, two suckers, the posterior sucker (acetabulum) terminal or ventro-terminal behind the genitalia, or at most embraced by the vitellaria. Skin with no spines. Excretory bladder a simple sac opening dorsally near hind end. Testes in
Family. ParamphistomidÆ, Fischoeder, 1901.
Amphistomata: Body not divided into a conical anterior portion and disc-like caudal portion. Ventral pouch absent.
Sub-family. ParamphistominÆ, Fisch., 1901.
ParamphistomidÆ: Oral sucker without evaginations. Not in man.
Sub-family. CladorchiinÆ, Fisch., 1901.
ParamphistomidÆ: Oral sucker with evaginations; testes, two, deeply cleft (fig.137). Genera: Watsonius, Cladorchis, etc.
Family. GastrodisciidÆ, Stiles and Goldberger, 1910.
Amphistomata: With body divided into a conical cephalic and disc-like caudal portion (fig.138). Posterior sucker ventro-terminal. Oral sucker with evaginations. Genera: Gastrodiscus and Homalogaster.
Group. Distomata, Retzius, 1782.
Gut forked, two suckers, the posterior sucker (acetabulum) ventral. It is always separated from the hind end by at least a part of the genitalia.
Family. FasciolidÆ, Railliet, 1895.
Large flat forms, genital pore in front of ventral sucker, the latter powerful. VitellariÆ of numerous follicles, united by branching vitellarian ducts, at the sides of the body meeting posteriorly and extending ventrally and dorsally. Cirrus and vagina without spines. No crown of strong spines around sucker. Testes much branched. Uterus not well developed. Excretory bladder much branched. Eggs large.
Sub-family. FasciolinÆ, Odhner, 1910.
Large or median forms, gut much branched. Body has a shoulder separating head from body. Receptaculum seminis absent. Ovary branched, ventral sucker in anterior part of body. Genus: Fasciola.
Sub-family. FasciolopsinÆ, Odhner, 1910.
Shoulder absent. Receptaculum seminis present. Ovary branched, gut takes a zig-zag course with kinks on it, ventral sucker in anterior part of body. Genus: Fasciolopsis.
Family. OpisthorchiidÆ, Braun, 1901, emend. auctor.
Ovary in front of testes. Small to medium flukes, very transparent, tapering anteriorly. Vitellaria moderately developed not extending in front of sucker. Cirrus absent. Seminal vesicle a twisted tube free in parenchyma. Testes near hind end one behind the other, lobed or branched, but not dendritically. Excretory bladder Y-shaped, the two limbs short, the stem S-shaped passing between the testes. Receptaculum seminis well developed. Laurer’s canal present. Uterine coils transverse, numerous. Eggs small.
Sub-family. OpisthorchiinÆ, Looss, 1899, emend. auctor.
OpisthorchiidÆ in which the excretory pore is terminal. Excretory bladder long, dorsal to testes. Uterine coils not overlapping gut forks. Genera: Opisthorchis, Paropisthorchis, Clonorchis, Amphimerus, etc.
Sub-family. MetorchiinÆ, LÜhe, 1909.
OpisthorchiidÆ in which the excretory pore is ventral. Excretory bladder short, ventral to testes. Uterine coils partly overlapping gut forks and extend anteriorly beyond the sucker. Vitellaria compressed on the sides of the body. Genus: Metorchis.
Family. DicrocoeliidÆ, Odhner, 1910.
Ovary behind testes. Testes behind the ventral sucker, between it and the ovary. Body thin and transparent. Cirrus sac encloses the pars prostatica and seminal vesicle. Skin smooth. Gut forks do not reach posterior end. Receptaculum seminis and Laurer’s canal present. Vitellaria, moderate, lateral in mid-body slightly overlapping the gut. Uterus with an ascending and descending branch and numerous transverse coils extending to hind end. Eggs dark brown, 25µ to 60µ. Excretory bladder tubular in posterior third or half of body. Parasitic in bile-ducts of mammals and birds. Genus: Dicrocoelium.
Family. HeterophyiidÆ, Odhner, 1914.
Ovary in front of testes. Genital pore behind or on a level with ventral sucker. Genital pore surrounded by a pseudo-sucker (i.e., its muscle is not sharply separated from but blends with the body muscles). Cirrus sac absent, consequently vesicula seminalis and pars prostatica lie free. Vagina and ejaculatory duct unite into a common duct before opening. Small and very small forms. Body covered with scales. Genera: Heterophyes, Metagonimus, etc.
Family. TroglotremidÆ, Odhner, 1914.
More or less flattened Distomes of compact form, 2 to 13mm. long. Ventral surface flat or somewhat hollowed, dorsal surface arched. Skin completely covered with pointed spines. Musculature weakly developed also in the suckers in those
Family. EchinostomidÆ, Looss, 1902.
More or less elongated flukes, small or very large, much flattened anteriorly, less so posteriorly, or even round. Suckers near one another, the anterior small and weak, the posterior large and powerful directed obliquely backwards. Surrounding the oral sucker dorsally and laterally but not ventrally is a fold or “collar” bearing a row or rows of pointed spines which are continued round laterally on to the ventral corners, the number being constant for each species, the corner spines large or specialized, skin anteriorly scaled or spiny. Alimentary canal consists of a pharynx, epithelial “pseudo-oesophagus” and gut cÆca reaching to posterior end. Testes behind one another in hind body. Ovary on right side or median directly in front of the testes. Vitellaria lateral, usually extending to the hind end and not beyond the ventral sucker anteriorly. Genital pore just in front of ventral sucker. Uterus in transverse loops. Genital sinus absent or present. Receptaculum seminis and Laurer’s canal present. Eggs thin shelled and large, bright yellow, 65µ to 120µ long. Excretory bladder Y-shaped. Parasitic in gut of vertebrates, especially birds.
Sub-family. EchinostominÆ, Looss, 1899.
Cirrus sac usually reaching to centre of ventral sucker, but not beyond. Cirrus long, usually without spines, coiled when retracted. Seminal vesicle tubular, twisted. On the head a ventral uniting ridge between the angles of the collar. Dorsal circlet of spines, single or double, not interrupted unless the collar itself is dorsally divided. Genera: Echinostoma, etc.
Sub-family. HimasthlinÆ, Odhner, 1910.
Cirrus sac reaching far beyond ventral sucker. Cirrus armed with strong rose-thorn-shaped hooks. Vesicula seminalis tubular not coiled. Cervical collar not continued across ventral aspect. Spines on collar in one row. Body armed with fine needle-shaped spines.
Family. SchistosomidÆ, Looss, 1899.
Sexes separate. Genital pore behind the ventral sucker. Ventral sucker elevated above the surface. Pharynx absent. Gut forks reunite to form a single stem. In ? four or more testicular follicles. In ? a single ovary, just in front of the union of the gut forks. Vitellaria on either side of the united gut stem.
The Trematodes Observed in Man.
Family. ParamphistomidÆ, Stiles and Goldberger, emend. 1910.
Sub-family. CladorchiinÆ, Fisch., 1901.
Genus. Watsonius, Stiles and Goldberger, 1910.
CladorchinÆ.—Body pyriform. Ventral pouch absent. Acetabulum ventral or (?) ventro-subterminal, very large, margins projecting, aperture small. Genital pore in front of bifurcation of gut, not surrounded by a sucker; ductus hermaphroditicus apparently absent. Excretory pore at posterior end of excretory vesicle, behind Laurer’s canal. Oral sucker with a pair of irregularly globular suctorial pouches; oesophagus thickened distally; cÆca long, not wavy; end in acetabular region.
Male Organs.—Testes two lobed, smaller than acetabulum; longitudinally, nearly or quite coinciding; transversely they abut or slightly overlap; preovarial in equatorial and caudal thirds. Pars musculosa not largely developed; cirrus pouch absent.
Female Organs.—Ovary and shell gland post-testicular. Vitellaria extend from gut fork to slightly beyond gut ending; uterus intercÆcal, partly post-testicular. Laurer’s canal in front of excretory vesicle.
Type Species.—Watsonius watsoni, Conyngham, 1904.
Watsonius watsoni, Stiles and Goldberger, 1910.
Syn.: Amphistomum watsoni, Conyngham, 1904; Cladorchis watsoni, Shipley, 1905.
Fig. 136.—Watsonius watsoni: ventral view. 4/1. (After Shipley.)
Body, 8 to 10mm. long, by 4 to 5mm. broad, by 4mm. thick; tapers anteriorly to 2·5mm. Caudal extremity bluntly rounded, venter surrounded by an elevated ridge, surface with transverse ridges best defined ventrally. Genital pore median about one-quarter of body length from anterior end at level of suctorial pouches. Acetabulum 1mm. in diameter, margin projecting, aperture small. Mouth in a groove with digitate papillÆ. Oral sucker very large, one-fifth of length of body, with a pair of irregularly globular pouches. Œsophagus somewhat longer than sucker. Excretory pore at the level of the acetabular aperture. The vesicle extends from the plane of the transverse vitelline ducts to centre of acetabulum.
Male Organs.—Testes deeply notched adjoining one another. Vesicula seminalis much coiled and dilated, pars musculosa not coiled. Pars prostatica (?) dilated, ejaculatory duct long and narrow, opening on a papilla; genital atrium papillated.
Female Organs.—Ovary dorso-posterior of posterior testis. Shell gland dorsal to ovary. Vitellaria ventral and lateral to gut cÆca extending from gut fork to equator of acetabulum. Uterus dorsal to testes, ductus hermaphroditicus absent. Laurer’s canal opens in dorso-median line slightly behind anterior border of sucker.
Fig. 137.—Watsonius watsoni: ventral projection composed from a series of transverse sections. o.s., oral sucker; s.p., suctorial pouch; ga., genital atrium; d.e., ejaculatory duct; es., oesophagus; e.g., oesophageal ganglion; p.p., pars prostatica; p.m., pars musculosa; i., gut; ut., uterus; v.e., vas efferens; v.e.s., left vas efferens; v.e.d., right vas efferens; v.g., vitellarium; t., testes; ov., ovary; s.g., shell gland; t.vd., transverse vitelline duct. (After Stiles and Goldberger.)
Eggs.—123µ to 133µ long by 75µ to 80µ broad.
Habitat.—Jejunum and duodenum of man, German West Africa. The parasite has only been found once in man. The patient, a negro from German West Africa, died at Zola, Northern Nigeria. The symptoms were persistent watery diarrhoea without blood or mucus. The parasites were also passed in the stools. It occurs also in monkeys.
Family. GastrodisciidÆ.
Genus. Gastrodiscus, Lkt., 1877.
Acetabulum small, caudal and ventral margin raised, aperture relatively large. Genital pore without sucker. Excretory pore post-vesicular, posterior to opening of Laurer’s canal. Œsophagus with muscular thickening; cÆca not wavy, long, end post-equatorial and post-testicular.
Male Genitalia.—Testes two, branched pre-ovarial.
Female genitalia.—Ovary and shell gland post-testicular. Vitellaria extracÆcal; uterus intercÆcal; Laurer’s canal entirely prevesicular.
Type.—Gastrodiscus Ægyptiacus, Cobbold, 1876.
Gastrodiscus hominis, Lewis and McConnell, 1876.267
Syn.: Amphistomum hominis, Lew. and McConn.
Body, reddish in the fresh, 5 to 8mm. long; posteriorly, 3 to 4mm. broad. The disc has incurved edges which are interrupted in front where it joins the anterior cylindrical portion and posteriorly behind the ventral sucker. The disc itself and ventral surface are covered with a number of (microscopic) papillÆ. Pharynx provided with two diverticula or pouches. The bifurcation of the gut lies sometimes above, sometimes below the level of the genital pore. The gut cÆca end about the level of the centre of the acetabulum.
Fig. 138.—Gastrodiscus hominis. Slightly magnified. (After Lerckart.)
Genital Pore.—About the middle of the conical anterior portion. (It appears to be surrounded by a muscular sucker.) Leiper (1913) describes the ducts as discharging at the tip of a large fleshy papilla, the surface of which bears cuticular bosses.
Testes much lobed, the anterior is smaller than the posterior and lies at about the level where the anterior conical portion joins the disc. The posterior testis just in front of the anterior margin of the acetabulum separated from it by the ovary. The ovary, somewhat oval in shape or slightly constricted in the middle, lies slightly to the right of the median line. Dorsal to it lies the well-developed shell gland, Laurer’s canal opening in front of the excretory bladder. The excretory bladder is a long sac with its opening at its posterior extremity about the level of the middle of the acetabulum. The
The eggs are oval and measure 150µ in length by 72µ in breadth.
Habitat.—CÆcum and large intestine of man. Also in the pig (5 per cent.) in Annam.
Distribution.—This parasite has been recorded from Assam (not uncommon), British Guiana (Indian immigrants), and Cochin China.
Gastrodiscus Ægyptiacus, Cobbold, 1876, and G. secundus, Looss, 1907, occur in the horse; G. minor, Leiper, 1913, in the pig in Nigeria and Uganda.
Family. FasciolidÆ, Raill., 1895.
Sub-family. FasciolinÆ, Odhner, 1910.
Genus. Fasciola, L., 1758.
The ventral sucker is situated at the level of the junction of the cone with the body, viz., at the level of the “shoulder,” and is large and powerful. The cuticle is covered with strong spines; the gut cÆca run in the mid-line to the hind end, and are provided with numerous long lateral and fewer and shorter median branches. The ovary lies on one side in front of the transverse vitelline duct; the testes lie obliquely one behind the other. The uterus, in the shape of a rosette, lies in front of the genitalia. Laurer’s canal is present; the vesicula seminalis lies in the cirrus pouch; the ova are large, not very numerous, and only develop after they have been deposited. Parasites of the biliary ducts of herbivorous animals.
Fasciola hepatica, L., 1758.
Syn.: Distomum hepaticum, Retz., 1786; Fasciola Humana, Gmel., 1789; Distomum caviÆ, Sons., 1890; Cladocoelium hepaticum, Stoss., 1892.
Fig. 139.—Fasciola hepatica, L. From a specimen that is not yet mature, showing the gut and its branches. 5/1.
Length 20 to 30mm., breadth 8 to 13mm., cephalic cone 4 to 5mm. in length and sharply differentiated from the body by a shoulder on each side. Spines in alternating transverse rows and extending on the ventral surface to the posterior border of the testes, and on the dorsal surface not quite so far. The spines are smaller on the cephalic cone than on the posterior part of the body, where they are discernible with the naked eye. The suckers are hemispherical, and near each other; the oral sucker is about 1mm. and the ventral sucker about 1·6mm. in diameter. The pharynx, which includes almost the entire
The Liver Fluke inhabits the bile-ducts of numerous herbivorous mammals (sheep, ox, goat, horse, ass, rabbit,268 guinea-pig, squirrel, beaver, deer, roe, antelope, camel, kangaroo, and others), and is distributed over the whole of Europe, though not to an equal extent. It is further known in North Africa, in North and South America, as well as in Australia; it is also found in Asia, as it has been reported from Japan, China, and Tonkin (Gaide, two cases in man). In some districts of Germany it is very frequent, and the slaughter-house statistics of various places show that it is of daily occurrence. Fasciola magna occurs in herbivora in America.
Fig. 140.—Fasciola hepatica. M., mouth; Ut., uterine rosette; Tr.c., transverse vitelline ducts uniting to form a vitelline receptacle in the mid-line; E.d., longitudinal vitelline ducts; V.s., vitellaria. The clear space in the centre represents the position of the ramifying testes and part of the gut. Natural size. (Mull. fluid, alcohol, creosote, Canada balsam.)
The liver fluke, however, is by no means a harmless parasite, for it produces in domestic animals, more especially in sheep, a disease of the liver that appears epidemically in certain years and districts, and commits great ravages amongst the flocks.
[The following records show the enormous loss caused in sheep by this parasite. In 1812, in the Midi, principally in the Departments of the RhÔne, Herault, and Gard, the disease was rampant; 300,000 sheep perished in the Arles territory, and 90,000 in the Arrondissements of NÎmes and Montpellier. In 1829 and 1830, in the Department
Fig. 141.—Fasciola hepatica, L. I., intestine; Vs., vitellaria; Ov., ovary; O., oral aperture; Ut., uterus; S., ventral sucker; T., testes. In front of the testes are seen the transverse vitelline ducts uniting to form the pyriform vitelline receptacle. Immediately in front of this the spherical shell gland. The two vasa efferentia can also be seen running up in the mid-line. The branches of the gut are only shown in the cephalic cone. (After Claus.)
The disease usually commences towards the end of summer with an enlargement of the liver, induced by the invasion of numerous young flukes; in the autumn and winter the animals suffer from the consequences of disordered biliary secretion; they become feverish, emaciated, and anÆmic, and lose their appetite. In consequence of the consecutive atrophy of the liver, oedema and ascites set in, and many animals succumb to this “liver rot.” On examination the liver is found to be shrunken, the bile-ducts are enormously dilated and in parts saccular and full of flukes. Should the animals survive this stage, spontaneous recovery ensues in consequence of the flukes commencing to leave the liver in the
[The following stages may be noticed in sheep suffering from fascioliasis. Gerlach recognized four stages, based on the varied relations that the flukes contract with the liver of their host. These periods are sometimes very marked, but at others, owing to subsequent infections, the features become merged and so obliterated. But when a single infestation occurs they are very marked.
Fig. 142.—Fasciola hepatica: egg from liver of sheep. o, operculum, e, segmenting ovum. The rest of the space is occupied by yolk cells, the granules in three only being shown. ×680. (After Thomas.)
[The first period is called the PERIOD OF IMMIGRATION. This occurs at the fall of the year and generally passes unperceived, as the young flukes do little harm to the liver. It varies from four to thirteen weeks. Gerlach has remarked upon cases of death from apoplexy at this period.
[The second period is the PERIOD OF ANÆMIA. This occurs in November and December. The sheep at first fatten rapidly, but later the mucous membranes become pale and of a yellowish hue, and the sheep become sluggish and cease to feed. The fÆces are normal, but may contain fluke ova.
[The third period is the PERIOD OF WASTING. This corresponds with the beginning of January—about three months after the
[The fourth period is the PERIOD OF MIGRATION OF THE FLUKES. This is a period of convalescence and recovery, generally in May and June.—F.V.T.]
Oxen suffer less in general, but even in these animals “stray” hepatic flukes are occasionally found in the lungs, enclosed in thick-walled cysts.
Pathological Anatomy.—The bile-ducts are conspicuous on the surface of the liver. They are thickened and much dilated and in parts saccular, and considerable atrophy of the liver cells accompanies the condition. Histologically there is immense proliferation of the epithelium of the bile-ducts leading to “adenomata.”
Fig. 143.—LimnÆus truncatulus, MÜll., the intermediate host of Fasciola hepatica. a., natural size; b., magnified. (From Leuckart.)
The LIFE-HISTORY of the liver fluke was discovered by R. Leuckart and P. Thomas. According to these investigators the elongated miracidium (fig.131, a) ciliated all over develops from the eggs a few weeks after the latter (fig.142) have reached the water, and after it has become free the embryo penetrates and becomes a sporocyst (fig.131, b) in a water-snail (LimnÆus truncatulus, MÜll. = L. minutus, Drap.) that is common in fresh water, and can live in the smallest collection of water as well as in fields that have been flooded. The sporocyst first of all produces rediÆ, which remain in the same host (and under certain circumstances, e.g. in summer, these develop a second generation of rediÆ), and these finally form cercariÆ (fig.134). The latter become encysted on blades of grass and are taken up by the respective hosts with their food; this takes place towards the end of summer, while the sheep feeding on the pasture land in the spring spread the eggs of the fluke, and sometimes the fluke itself, by passing them with their fÆces.
In districts where LimnÆus truncatulus is absent, analogous species act as the intermediary hosts, of which one example according to Lutz is LimnÆus oahuensis in the Sandwich Islands.
[The host in Europe is LimnÆus truncatulus. This snail extends from Siberia to Sicily and Algeria, and according to Captain Hutton is a native of Afghanistan. It also occurs in
[In South America the host is probably LimnÆus viator, Orb., and in North America LimnÆus humilis, Say.—F.V.T.]
In human beings as well as in some of the mammals quoted above, the liver fluke is only a casual parasite, and hitherto only twenty-eight cases have been observed in man; the infection was mostly a mild one and there were no symptoms, or only very trifling ones; a few isolated cases were only discovered post mortem. Occasionally, however, even when the infection was inconsiderable, severe symptoms were set up, which in isolated cases led to death. The symptoms (enlargement and painfulness of the liver, icterus) merely pointed to a disease of the liver.
Diagnosis can only be established by finding eggs in the fÆces. Care should be taken not to confuse them with those of Dibothriocephalus latus.
Halzoun.
Fig. 144.—Young Fasciola hepatica, soon after entry into the liver. The intestinal cÆca have lateral diverticula. Magnified. (From Leuckart.)
In North Lebanon, the liver fluke is, according to A. Khouri, a frequent parasite of man, not in the liver, however, but in the pharynx. The occurrence in this unusual site is effected by the eating of raw infected livers, especially those of goats (Capra hircus). The flukes thus taken in do not all reach the stomach, where they would be soon killed, but some of them attach themselves to the pharyngeal mucosa and to the adjoining parts, and there cause inflammation and swelling, which lead to dyspnoea, dysphagia, dysphonia and congestion of the head, sometimes even to still more severe symptoms, and even death. The affection termed “Halzoun” lasts some hours or several days, and after vomiting recovery sets in. In other cases man becomes infected in the usual way by ingesting cysts attached to grass or the underside of leaves of plants (e.g., Rumex sp.), where they
As the liver fluke feeds on blood it is possible that it also reaches, particularly when young, the circulatory system, and cases have been known in which it has been carried by the blood into organs far from its original situation. Such cases also have been repeatedly observed in men. Probably the parasite described by Treutler, 1793, as Hexathyridium venarum, which protruded from the ruptured anterior tibial vein of a man, was a young liver fluke. A few adult specimens were found by Duval in the portal and other veins post mortem at Rennes (1842) in a man, aged 49, and a similar statement is reported by Vital from Constantine (1874). Giesker, in 1850, found two hepatic flukes in a swelling on the sole of the foot of a woman. Penn Harris states that he observed six specimens in Liverpool in a spontaneously ruptured abscess of the occiput of a two months old infant. Another case which, like the previous
Fig. 145.—Fasciola gigantica. ×6 12 (After Looss.)
From such records it is not impossible that Distomum oculi humani, Ammon, 1833, as well as Monostomum lentis, v. Nordm., 1832, may have been very young hepatic flukes that had strayed. Ammon found four specimens (length 0·5 to 1mm.) of his species (named Distomum ophthalmobium by Diesing in 1850) between the opaque lens and the capsule of a five months old child in Dresden, and von Nordmann discovered his Monostomum lentis to the number of eight specimens (only 0·3mm. in length) in the opaque lens of an old woman. Minute white bodies which Greef found in the cortex of the lens of a fisherman, aged 55, removed on account of cataract, were with some reserve regarded as Trematode larvÆ. The fact that Ammon found that the intestinal cÆca of the worm discovered by him had no lateral branches does not negative the above opinion, as in the liver fluke the intestinal cÆca are originally unbranched, and according to Lutz they only develop lateral ramifications later, between the twelfth and twenty-second day of infection (fig.144).
Fasciola gigantica, Cobbold, 1856.
Syn.: Distomum giganteum, Diesing, 1858; Fasciola gigantea, Cobbold, 1858; Cladocoelium giganteum, Stoss., 1892; Fasciola hepatica var. angusta, Raill., 1895; Fasciola hepatica var. Ægyptiaca, Looss, 1896.
This species is closely allied to Fasciola hepatica, but is distinguished by its elongated body, short cephalic cone, almost parallel sides, larger ventral sucker, which is also closer to the oral sucker, and by its larger eggs. Length up to 75mm., width up to 12mm. Oral sucker 1 to 1·2mm., ventral sucker up to 1·7mm. in diameter. Eggs 150µ to 190µ long by 75µ to 90µ broad.
Habitat.—Bile-ducts of Camelopardalis giraffa, Bos taurus, Bos indicus, Bos bubalis, Ovis aries and Capra hircus.
Distribution.—Africa.
This species has once been observed in man by Gouvea, in Rio de Janeiro, in a French naval officer who became ill with fever, cough and slight blood-spitting. The lungs were normal except for a
Sub-family. FasciolopsinÆ, Odhner, 1910.
Genus. Fasciolopsis, Looss, 1898.
Ventral sucker large, and elongated posteriorly into a sac. Cirrus pouch long and cylindrical, its greatest length being occupied by the sinuous tubular seminal vesicle, on which exists a peculiar cÆcal appendage. Laurer’s canal present.
Fasciolopsis buski, Lank., 1857.
Syn.: Distomum buski, Lank., 1857; Dist. crassum, Cobbold, 1860, nec v. Sieb., 1836.
Fig. 146.—Fasciolopsis buski, Lank. V.s., ventral sucker; C.p., cirrus pouch; I., intestinal fork; S.v., vitellaria; T., testes; O., ovary; Ms., sucker; Shg., shell gland; Ut., uterus. Magnified. (After Odhner.)
The length of the body varies; it may measure 24 to 37 or even attain 70mm.; the breadth is from 5·5 to 12 to 14mm. In the pig the fresh parasites measure, smallest, 12 to 8mm.; largest, 35 to 16mm. (Mathis and LÉger). Skin without spines, but according to Heanly always present in man and pig specimens. The oral sucker measures 0·5mm. in diameter; the ventral sucker is three to four times as large; the pharynx is globular, 0·7mm. in diameter; the prepharynx is provided with a sphincter; the intestinal cÆca extend to the posterior border with
Habitat.—Intestine of pig and man.
Distribution.—In man: India, Siam, China, Assam, Sumatra. It is common in Cochin China (16 out of 133 Annamites, Noc.), in Tonkin very rare. Dr. J. Bell has sent me [J.W.W.S.] human specimens from Hong Kong. In pigs: very common in South China (Heanly). Common in pigs in Hong Kong. Sixteen out of 248 pigs (i.e., 6 per cent.) infected in Hanoi.
Fasciolopsis rathouisi, Ward, 1903.
Syn.: Distomum rathouisi, Poirier, 1887.
Fig. 147.—Fasciolopsis rathouisi, Poir.: the mouth at the top, and under it the genital pore and ventral sucker, behind which again is the uterus. The vitellaria are at the sides, and posteriorly in the central field the ramified testes; the ovary is in front of the right testis. (After Claus.)
Fifteen to 19mm. long by 8·5 to 10·5mm. broad by about 3mm. thick. Skin with spines (Leiper). Bluntly oval or elliptical with short cephalic cone which is absent in Fasciolopsis buski. Oral sucker subterminal, 0·25 to 0·29mm. broad by 0·2mm. in antero-posterior diameter. Distant from ventral sucker by about twice its diameter. Ventral sucker 1·32 to 1·38mm. broad by 0·68 to 0·7mm. in antero-posterior diameter. Œsophagus extremely short. Cirrus sac not conspicuous and straight as in Fasciolopsis buski, but is convoluted. Testes one behind the other (according to Poirier they lie beside one
Habitat.—Intestine of man.
Distribution.—China, common in some parts (Goddard).
Fasciolopsis goddardi, Ward, 1910.
Twenty-one to 22mm. long, 9mm. broad. Skin with spines (Leiper). Uterus very closely coiled, most striking character is the large size of the vitelline acini. Imperfectly known.
Distribution.—China (Shanghai).
Fasciolopsis fÜlleborni, Rodenwaldt, 1909.
The fully extended fluke is tongue-shaped, 50 by 14mm.; two contracted specimens measured 40 by 15mm. and 30 by 16mm. respectively. Skin without spines, with according to Leiper cephalic cone not clearly defined. Oral sucker circular, 0·75mm. in diameter, slightly larger than that of Fasciolopsis buski. Ventral sucker 2·6mm. in diameter (that of Fasciolopsis buski 1·6 to 2mm.). Length 2·9mm. (as in Fasciolopsis rathouisi), the excess of length over breadth being due to the posterior elongated sac-like prolongation of the sucker. Prepharyngeal sphincter present. Pharynx 0·7mm. in diameter. Œsophagus practically absent. Gut cÆca similar to those of Fasciolopsis buski.
Testes—regularly branched, separated by an incurving of the cÆca, the anterior occupying a smaller area than the posterior.
Ovary—very small, as in Fasciolopsis buski, on the right side.
Shell Gland—almond-shaped, 2·3 by 1·2mm. In Fasciolopsis buski it is round and smaller, 1 to 1·5mm. in diameter.
Vitellaria—similar in distribution to those of Fasciolopsis buski, but the acini are strikingly small.
Fig. 148.—Fasciolopsis fÜlleborni, ventral aspect. (After FÜlleborn.)
Cirrus Sac—is the most characteristic feature of this species. It is a powerfully built, convoluted sac standing out clearly on the body.
Seminal Vesicle—has a peculiar convoluted, saccular and angular course, but the cÆcal appendage characteristic of the genus appears to be absent!
Excretory System.—The main stem gives off very regular transverse branches which are well seen posteriorly.
Eggs.—100µ by 73µ. Thin shelled.
Habitat.—Intestine. Mahommedan from Calcutta.
[It is evident that a re-examination of fresh material is required before the validity of all these species can be accepted.—J.W.W.S.]
Family. TroglotremidÆ, Odhner, 1914.
Genus. Paragonimus, Braun, 1899.
Body egg-shaped or somewhat elongated, generally more broadly rounded in front than behind. Covered all over with spear-shaped spines arranged in groups. Gut cÆca winding with dilatations or constrictions in parts. Ventral sucker in or in front of the middle of the body. Excretory bladder cylindrical, very long and broad, reaching in front to the bifurcation of the gut. The lateral excretory canals join the bladder only a little in front of the excretory pore. Genital pore median just behind the ventral sucker. Genital sinus duct-like. Cirrus sac absent. Male terminal organs very small. Ejaculatory duct present. Testes and ovary deeply lobed, the testes in or just behind the middle, the ovary somewhat laterally placed just behind the ventral sucker. Uterus forms a coil behind the ventral sucker. Eggs rather large, thin shelled, the ovarian cell still unsegmented on deposition. Receptaculum seminis, small.
Parasitic in the lungs of mammals, enclosed in cyst-like cavities, generally in pairs.
Type Species.—P. westermanii in the tiger.
Paragonimus ringeri, Cobb., 1880.
Syn.: Distoma ringeri, Cobb., 1880; Distoma pulmonale, Baelz, 1883; Distoma pulmonis, Suga, 1883.
Fig. 149.—Paragonimus ringeri, Cobb.: to the right, dorsal aspect; to the left, ventral aspect. Natural size. (After Katsurada.)
The body is of a faint reddish-brown colour and plump oval shape. The ventral surface a little flattened; 7·5 to 12mm. in length, 4 to 6mm. in breadth, and 3·5 to 5mm. thick (in man). The oral sucker (0·75mm.) is subterminal; the ventral sucker (0·8mm.) somewhat in front of the middle of the body. Pharynx spherical,
Fig. 150.—Paragonimus ringeri, Cobb.: diagram of the internal organs. a, oesophagus; b, vitellaria (a portion only shown); c, common genital duct; d, shell gland with oviduct, Laurer’s canal and vitelline duct; e, ovary; f, vitelline receptacle; g, excretory pore; h, oral sucker; i, pharynx; k, gut; l, ventral sucker; m, uterine coils; n, vitellarian ducts; o, vas efferens; p, testis. (After Kubo.)
Fig. 150a.—Paragonimus westermanii, Kerb.: seen from the ventral surface. Mouth, pharynx, intestinal cÆca, at the sides of which the vitellaria are observed. The genital pore is behind the ventral sucker, and next to it, on the left, the ovary; on the right, the uterus; the two testes posteriorly; the excretory vessel in the middle, 10/1. (After Leuckart.)
The following species are also known:—P. westermanii, Kerb., 1878, in the tiger, and P. kellicotti, Ward, 1908, in the pig, dog, and
| P. ringeri. | P. westermanii. | P. kellicotti. | |
| Shape | Chisel-shaped, mod- erately heavy. | Lancet-shaped, very slender. | Chisel-shaped, heavy. |
| Distribution | Circular rows, in groups. | Circular rows, in groups. | Circular rows, singly. |
Two other species, P. rudis, Diesing, 1850, in a Brazilian otter (Lutra brasiliensis) and P. compactus, Cobbold, 1859, in the Indian ichneumon, are but little known.
Habitat.—Lungs, pleurÆ, and especially the bronchi of man and dog. The alleged occurrence (of eggs) in other organs may be due to confusion with those of Schistosoma japonicum.
Fig. 151.—Egg of Paragonimus ringeri, Cobb., from the sputum. Showing the ovarian cell and vitelline cells and granules. 1,000/1. (After Katsurada.)
Distribution.—China, Korea, and especially in Japan, where, according to Katsurada, there are no districts that are entirely free from pulmonary flukes. The mountainous provinces of Okayama, Kumamoto, Nagano and Tokushima are the principal centres.
Pathology.—The number present in the lung varies from two to twenty, about. Usually one cyst contains one worm, but in the dog each cyst contains two. The cysts admit the tip of the finger, and have a fibrous wall 1mm. thick. They originate partly from dilatation of bronchi and bronchioles. Others arise from the inflammatory reaction of lung tissue into which the worms have wandered. The worms and their eggs cause bronchitis and peribronchitis, catarrhal, hÆmorrhagic, or purulent, and areas of consolidation. Areas containing eggs in their centre resembling tubercle nodules are not uncommon, and extensive cirrhosis of the lung may be found. As a result of these changes, emphysema and bronchiectasis also occur.
As to the development, only the following details are known: that the eggs, which before segmentation of the ovum reach the open in the sputum and through being swallowed also in the fÆces, develop in water into a miracidium ciliated all over, which hatches and swims about freely. According to Manson this takes place in four to six weeks.
Sub-family. OpisthorchiinÆ, Looss, 1899.
Genus. Opisthorchis, R. Blanch., 1845.
OpisthorchiinÆ with lobed testes. Laurer’s canal present. Parasitic in the bile-ducts of mammals and birds.
Opisthorchis felineus, Riv., 1885.
Syn.: Distoma conus, Gurlt, 1831 (nec Creplin, 1825); Distoma lanceolatum, v. Sieb., 1836, v. Tright, 1889 (nec Mehlis, 1825 = Fasciolo lanceolata, Rud., 1803); Distoma sibiricum, Winogr., 1892; Distoma tenuicolle, MÜhl., 1896.
Fig. 152.—Egg of Opisthorchis felineus, Riv. 830/1.
This parasite is yellowish-red in the fresh condition, and almost transparent. The body is flat, with a conical neck at the level of the ventral sucker marked by a shallow constriction; this, however, is only noticeable in fresh and somewhat contracted specimens. Posteriorly to the ventral sucker the lateral borders run fairly parallel; the posterior end is either pointed or rounded off. The length and breadth vary according to the contraction, being usually 8 to 11mm. by 1·5 to 2mm. The suckers are about one-fifth to one-sixth of the length of the body distant from each other, and of about equal size (0·23 to 0·25mm.). The oesophagus is hardly any longer than the pharynx, which lies close behind the oral sucker; the intestinal cÆca reach almost to the posterior border and are often filled with blood. The excretory pore is at the posterior extremity, and the excretory bladder forks in front of the anterior testis. The testes in the posterior fourth of the body lie obliquely one behind the other; the anterior one has four lobes, the posterior one five lobes; the ovary is in the median line transversely, simple or slightly lobed; behind it lies the large pear- or retort-shaped receptaculum seminis and Laurer’s canal. The uterus is in the median field. The vitellaria occupy the fairly broad lateral areas, in about the central third of the body, beginning behind the ventral sucker and terminating at about the level of the ovary; the acini are small and arranged in groups of seven to eight, separated by interstices. The genital pore is close in front of the ventral sucker. The eggs are oval with sharply defined operculum at the pointed pole, 30µ, by 11µ.
Fig. 153.—Opisthorchis felineus: from the cat. m., mouth; p.b., pharynx; i., gut; g.p., genital pore; ac., ventral sucker; ut., uterus; v.g., vitellarium; ov., ovary; s.g., shell gland; r.s., receptaculum seminis; t. testes; ex. p., excretory pore. (After Stiles and Hassall.)
This species, which is frequently confused with others, inhabits the gall-bladder and bile-ducts of the domestic cat especially; but is also found in the dog, in the fox, and in the glutton (Gulo borealis). It has been observed in France, Holland, North Germany (being particularly frequent in East Prussia), in Russia, Scandinavia, Siberia, Japan, Tonkin, Hungary, and Italy. The North American form (from cats and Canis latrans) is a distinct species (Opisthorchis pseudofelineus).
In man this species was first found by Winogradoff in Tomsk (nine cases), then by Kholodkowsky in a peasant from the neighbourhood
In none of Winogradoff’s nine cases had the death of the patient been caused direct by the parasites, yet more or less extensive changes in the liver were found in all of them; such as dilatation of the bile-ducts with inflammation and thickening of their walls, and foci of inflammation or atrophy in the liver substance; icterus was present five times and atrophy of the liver an equal number of times; ascites was observed three times, and in two cases, probably of recent date, the organ was enlarged. The number of parasites found fluctuated between a few and several hundreds.
In two of Askanazy’s cases, which he examined more closely, carcinoma which had developed at the places most invaded by flukes was found at the post-mortem, so that perhaps there may be grounds for the connection which the author seeks to establish between cancer of the liver and the changes induced by the parasites; these changes consist of numerous and even ramified
Fig. 154.—Opisthorchis pseudofelineus: from the bile-duct of the cat (Iowa), m., oral sucker; p.b., pharyngeal bulb; es., oesophagus; i., intestine; va., vagina; g.p.m., male orifice; ac., ventral sucker; ut., uterus; v.g. vitellarium; s.g., shell gland; v.dt., vitelline duct; ov., ovary; r.s., receptaculum seminis; L.c., Laurer’s canal; t., testis; ex.c., excretory bladder; ex.p., excretory pore. (After Stiles.)
Winogradoff as well as Askanazy found isolated flukes in the intestine also.
Unfortunately, nothing much is known of the history of the development of Opisthorchis felineus; we only know that when deposited the eggs already contain a ciliated miracidium, which, however, according to my experience, does not hatch out in water, but only after the entry of the eggs into the intestine of young LimnÆus stagnalis; no further development, however, occurs. Winogradoff states that he has seen the miracidia hatch after the eggs had been kept in water for a month at 37°C.; and has even observed free miracidia in the bile of man and of a dog respectively. Although the whole post-embryonal development of the cat fluke remains yet to be investigated, Askanazy by a series of experiments on cats and dogs has discovered the mode of infection. The intermediate hosts are fish, and mainly the ide, in this country called Tapar (Idus melanotus, H. and Kr.), and of subsidiary importance the
In one of his nine cases Winogradoff also saw a small fluke covered all over with spines, which he conjectured to be the young stage of Opisthorchis felineus; as, however, according to my experience, this species, even in smaller specimens, is always without spines, the above hypothesis cannot be accepted. It is much more probable that one of the other species that also invade the liver of cats may accidentally be introduced into man; we know, in fact, that Metorchis albidus, Braun, and Metorchis truncatus, Rud., are both covered with spines. As, however, the spines of the first-named species are rather apt to fall off, and also as it possesses a different shape (spatula-shaped), it may be assumed that probably Winogradoff had found Metorchis truncatus, Rud., 1819, in his patient.
Genus. Paropisthorchis, Stephens, 1912.
Structure as in Opisthorchis, except that the ventral sucker and genital pore occur on the apex of a process or pedicle projecting from the anterior portion of the body. This process is about 12mm. long, and is retractile.
Paropisthorchis caninus, Barker, 1912.
Syn.: Distoma conjunctum, Lewis and Cunningham, 1872; Opisthorchis noverca, M. Braun, 1903 (pro parte); Opisthorchis caninus, Barker, 1912 (?).
Length varies from 2·75 to 5·75mm. in preserved specimens, average 3·6 to 5·2mm. Body uniformly spinose, though as a rule spines are not present on the pedicle. Body slightly concavo-convex, the concavity being ventral. Oral sucker 0·28mm. Pharynx 0·224 by 0·184mm. Œsophagus 0·04mm. Ventral sucker 0·176mm. in diameter. Pedicle about 12mm. long, may be completely retracted.
Fig. 155.—Paropisthorchis caninus: from the bile-ducts of the pariah dog, India. Acet. v., ventral sucker; Ut., uterus; V. ex. lat., longitudinal excretory duct; V. sem., seminal vesicle; Sem. rec., seminal receptacle; Ov., ovary; V. ex., excretory bladder; Test. l., left testis; Test. r., right testis; P. ex., excretory pore. ×40. (After Stephens.)
Genital Pore—opens on the apex of the pedicle in front of the ventral sucker. Its exact position varies with the state of contraction of the parts. In certain cases it actually opens within the cuticular border of the sucker, in other cases it opens externally to the sucker and anterior to it. The opening is covered with scales. The vas deferens and uterus run alongside one another until they merge near the apex of the pedicle into a common sinus.
Vitellaria—consist of eight acini on each side, extending from slightly behind the base of the pedicle to the anterior border of the ovary, or as far back as a line separating the posterior border of the ovary from the anterior border of the anterior testis.
Testes.—Anterior testis 0·496 by 0·44mm.; posterior testis 0·52 by 0·48mm., usually ovoid, though both may be regularly lobed. The anterior testis is usually on the left side.
Ovary—multilobular, the lobes 6 to 8 being irregular in size and shape.
Shell Gland—extensive and diffuse, occupying an area which approximately corresponds with the loop of the transverse vitelline ducts.
Seminal Receptacle—globular, to the right of and dorsal to the posterior lobe of the ovary.
Laurer’s Canal—generally runs from the end of the receptacle with a single curve medially and backwards.
Uterine Coils—form loosely packed transverse coils terminating slightly in front of the level of the first vitelline acini. From here the uterus passes forwards into the pedicle to the left and ventral to the seminal vesicle.
Seminal Vesicle—commences about the level of the first vitelline acini. The coils displace the uterus ventrally and to the left. In the pedicle the vesicle diminishes in extent and lies in its dorsal (anterior) side.
Habitat.—Liver of pariah dogs, India. In North-Western Provinces about 40 per cent. are infected. This fluke appears to be different from Amphimerus (Opisthorchis) noverca in man, as the latter has not the pedicle on the summit of which lie the sucker and common genital pore.
Fig. 156.—Amphimerus noverca, Braun. o.s., oral sucker; p.b., pharynx; ac., ventral sucker; ut., uterus; v.g., vitellarium; ov., ovary; v.d., vas efferens; ex.c., excretory canal; t., testis. (After McConnell.)
Genus. Amphimerus, Barker, 1912 (?).
Structure as in Opisthorchis, except that the vitellaria are separated into two portions, an ant-ovarial and a post-ovarial.
Amphimerus noverca, Barker, 1912 (?).
Syn.: Distomum conjunctum, McConnell, 1876 (nec Cobbold, 1859); Opisthorchis noverca, M. Braun, 1903 pro parte.
At the autopsy of two Mahommedans who died in Calcutta, McConnell found a large number of Distomata in the thickened and dilated bile-ducts. The worms were lancet-shaped, covered with spines, and measured 9·5 to 12·7mm. in length and 2·5mm. in breadth. The two suckers lie very close to one another, the anterior one being larger than the ventral; the genital pore opens immediately in front of the ventral sucker; pharynx spherical; intestinal cÆca extending far back. At the commencement of the posterior third of the body the two testes, somewhat apart, the anterior one roundish, the posterior one distinctly lobed. The transverse and slightly lobed ovary in front of the bifurcation of the Y-shaped excretory bladder, whence the uterus, in convolutions barely spreading beyond the central field, extends to the pore; the vitellaria in the lateral areas commence behind the ventral sucker and extend to the testes. Cirrus pouch absent. Eggs oval, 34µ by 21µ.
Genus. Clonorchis, Looss, 1907.
Structure as in Opisthorchis, distinguished, however, by the branched testes situated one behind the other, the branches of which ventrally encroach upon the gut forks; dorsal to the testes the S-shaped excretory bladder, the main branches of which, arising at the level of the bifurcation of the gut, open into the bladder below its anterior end. Parasitic in the bile-ducts of mammals and man.
Fig. 157.—Metorchis conjunctus,272 (Syn.: Distomum conjunctum, Cobb., nec Lew. and Cunn., nec McConn.): from Canis fulvus. Vs., ventral sucker; I., intestine; Vsc. vitellaria; Ex., excretory bladder; T., testes; O., ovary; Ms., oral sucker; Ph., pharynx; Ut., uterus. (After Cobbold.)
Fig. 158.—Clonorchis sinensis. C.L., Laurer’s canal; Dst., vitellaria; Ex., excretory bladder; H., testes; K., ovary; R.s., receptaculum seminis; Vd., terminal section of vas deferens. Magnified 4 12 times. (After Looss.)
Clonorchis sinensis, Cobbold, 1875.
Syn.: Distoma sinense, Cobbold, 1875; Distoma spathulatum, R. Leuckart, 1876 (nec Rudolphi, 1819); Distoma hepatis innocuum, Baelz, 1883.
In shape resembles Opisthorchis felineus, 13 to 19mm. long, 3 to 4mm. broad, at the beginning of sexual maturity 12 to 13mm. long, 2·5 to 3mm. broad. Oral sticker 0·58 to 0·62mm., ventral sucker 0·45 to
Eggs 26µ to 30µ by 15µ to 17µ. Average 29µ by 16µ.
Fig. 159.—Ova of Clonorchis sinensis. The knobs on the ends of the eggs are not shown. 900/1. (After Looss.)
This (?) species was discovered in 1874 by McConnell, in Calcutta, in the bile-ducts of a Chinaman who died shortly after being admitted into hospital.
Habitat.—Bile-ducts of man, dog and cat.
Distribution.—Especially in China, apparently rare in Japan.
Clonorchis endemicus, Baelz, 1883.
Syn.: Distoma sinense s. spathulatum p.p.; Distoma hepatis endemicum s. perniciosum, Baelz, 1883; Distoma japonicum, R. Blanchard, 1886.
Fig. 160.—Clonorchis endemicus. ×6 about. (After Looss.)
Very similar to the previous species and consequently generally confused with it. Length between 6 and 13mm., width varying between 1·8 and 2·6mm. Oral sucker 0·37 to 0·5mm., usually 0·43 to 0·45mm. in transverse diameter; ventral sucker 0·33 to 0·45mm., usually 0·37 to 0·40mm. No pigment in parenchyma; anterior testis with four, posterior testis with five branches. Vitellaria continuous, ova 26µ by 13µ to 16µ.
Habitat.—Bile-ducts of man, dog, cat and pig.
Distribution.—This species occurs very frequently in man, in certain districts of Japan, especially in the province of Okayama, Central Japan, in particular localities of which above 60 per cent. of the population are infected. The worms are sometimes found in enormous numbers in the liver (upwards of 4,000), also in the pancreas and rarely in the duodenum. It is common in Tonkin and Indo-China. LÉger in Tonkin found 50 per cent. of people apparently in normal health infected, so that probably symptoms only arise when the infection is intense. [The exact distribution of these two species is, however, not precisely defined at present, as commonly no distinction is made between them.—J. W.W.S.]
Fig. 161.—Clonorchis endemicus: eggs. The knobs on the eggs are not shown. ×900. (After Looss.)
Verdun and Bruyant deny, in opposition to Looss, the possibility of being able to distinguish within the genus Clonorchis the two species described, but they admit the justification for the new genus. They also report the occurrence of Opisthorchis felineus in man in Tonkin (Compt. Rend. Soc. de Biol., lxii, 1907).
Pathology.—Both species of Clonorchis give rise to grave symptoms. The liver is generally enlarged, though when the infection has lasted some time it begins to contract. The surface of the organ is studded with white vesicles, and on cutting into it one sees numerous cavities with thickened walls (distended bile-ducts) filled with a brownish fluid containing innumerable eggs, which cause its colour. Microscopically, the epithelium of the bile-ducts is either (1) entirely destroyed, or (2) actively proliferates, forming an adenomatous outgrowth. Occasionally this proliferation is not limited by the wall of the bile-duct but penetrates it and leads to a growth of numerous new ducts, forming a
To what extent blood or bile respectively forms the food of the flukes is uncertain.
Life-history.—(Kobayashi, 1911, Mitteilungen aus dem kaiserlichen Institut fÜr Infektions-Krankheiten zu Tokio, pp.58–62.)
It results from the work of Kobayashi in Japan that fresh-water fish form the second intermediate host for Clonorchis endemicus. He fed cats with encysted flukes (cercariÆ) from various fish and easily succeeded in infecting them, e.g. a kitten, proved to be uninfected by repeated examination of its fÆces, was fed on infected fish; a month later innumerable flukes were found in the bile-ducts, gall-bladder, pancreas and even in the duodenum. The fish infected were Leucogobis gÜntheri, Pseudorasbora parva, and to a less extent Acheclognathus lanceolata, Acheclognathus limbata, Paracheclognathus rhombea, Pseudoperilampus typus, Abbottina psegma, Biwia zezera and Sarcocheilichthys variegatus. The cysts occur throughout the muscles and subcutaneous tissue of the fish. Length 0·13mm., breadth 0·1mm. The cercaria lies folded in the cyst, length 0·5mm. breadth 0·1mm. It tapers posteriorly. Skin at first covered with fine spines, disappearing as they grow older. Body dotted with fine pigment.
The first intermediate host is still unknown.
Sub-family. MetorchiinÆ, LÜhe, 1909.
Genus. Metorchis, Looss, 1899, emend. auctor.
Hind end rounded. Gut forks reach extreme end. Testes only slightly lobed, filling the hind end.
Metorchis truncatus, Rud., 1819.
Fig. 162.—Metorchis truncatus, Rud.: from the biliary ducts of the domestic cat. V.s., ventral sucker; I., gut; V.sc., vitellaria; T., testes; O., ovary; R.s., receptaculum seminis; Ut., uterus. 25/1.
This species, which attains a length of 2mm., is slender and conical, the anterior end is pointed and the posterior truncated, and provided with a muscular tuberosity that resembles a terminal sucker; for this reason the discoverer of the species (Rudolphi) classed it with the Amphistomes. The cuticle in the young, as well as in the adult specimens, is entirely and closely covered with spines. Suckers about equal in size (0·134 to 0·172mm.); the ventral sticker lies somewhat
Metorchis truncatus lives in the bile-ducts of the seal, cat, dog, fox, and glutton (Gulo borealis). The source of infection is unknown, although one would suspect fish. Askanazy did not succeed in getting this fluke in his feeding experiments, but another species, Metorchis albidus, not uncommon in cats by feeding them on roach (Leuciscus rutilus).
Family. HeterophyiidÆ, Odhner, 1914.
Genus. Heterophyes, Cobbold, 1866.
Syn.: Cotylogonimus, LÜhe, 1899; CÆnogonimus, Looss, 1899.
No crown of spines on head. Body divided into a narrow, movable, anterior part (neck), and a broader, less movable, posterior portion, which contains the genitalia. The suckers separated from one another by a space equal to half the length of the body or more; the pharynx is close behind the oral sucker; the oesophagus is long; the intestinal cÆca extend to the posterior border; the genital pore is placed laterally, and behind the ventral sucker. Genital sucker provided with a circlet of chitinous rodlets, shaped like stags’ horns. The testes are at the posterior end, the ovary in a median position in front of them. Laurer’s canal with receptaculum seminis present; the small vitellaria are at the sides of the posterior part of the body. Parasitic in the intestine of mammals and birds.
Heterophyes heterophyes, v. Sieb., 1852.
Syn.: Distomum heterophyes, v. Siebold, 1852; Heterophyes Ægyptica, Cobbold, 1866; Mesogonimus heterophyes, Railliet, 1890; Coenogonimus heterophyes, Looss 1900; Cotylogonimus heterophyes, Braun, 1901.
Length up to 2mm., breadth 0·4mm.; the neck not sharply defined; in life it stretches to double the length of the hind body. The scales are rectangular, 5µ to 6µ by 4µ, their posterior margin serrate with seven to nine teeth. Cuticular glands are numerous on the ventral surface, especially in the fore part of the body, and partly discharge at the anterior border of the oral sucker. The oral sucker is 0·09mm., the ventral sucker 0·23mm. in diameter; the pharynx measures 0·05 to 0·07mm. in length; the oesophagus is about three times as long; posteriorly the intestinal cÆca are directed one towards the other and terminate beside the excretory bladder. Close in front of the posterior ends of the intestinal branches are the two elliptical testes, which are not exactly on the same level. In the middle in front of them is the receptaculum seminis, and in front of the latter lies the spherical or elliptical ovary. The two vasa efferentia unite to form the vas deferens, which after a short course passes over into the angularly bent seminal vesicle; after the entry of the prostatic glands it becomes united with the metraterm (vagina), and the common duct opens into the genital sucker. The latter is somewhat smaller than the ventral sucker, lateral to and close (0·15mm.) behind it, and bears a not entirely closed ring of from seventy-five to eighty chitinous rods (20µ in length). The vitellaria on either side consist of about fourteen acini. The uterus is spread almost throughout the entire posterior part of the body. The eggs have thick shells with a knob resembling that of Clonorchis eggs but not so prominent, and measure 30µ by 17µ; they contain a completely ciliated miracidium with a rudimentary intestinal sac.
Fig. 163.—Heterophyes heterophyes, v. Sieb. C., cerebral ganglion; I., intestinal cÆca; Ct.g., cuticular glands; V.sc., vitellaria; Ut., genital sucker; T., testes—the excretory bladder between them; L.c., Laurer’s canal; R.s., receptaculum seminis, with the ovary in front of it; G.c., ventral sucker; Vs., vesicula seminalis, 53/1. On the left side above, an egg, 700/1, is depicted, and below it three chitinous rodlets from the genital sucker. 700/1. (After Looss.)
This species was discovered in 1851 by Bilharz in the intestine of a boy who died in Cairo; a second case was only found in 1891 and published by R. Blanchard, so that it appeared as if the species were very scarce. According to Looss, this is, however, not the case, but the species easily escapes notice on account of its small size. Looss found it in Alexandria twice in nine autopsies, and once in Cairo, and has recently stated that in man “it is not at all uncommon to meet with the parasite in cadavers, and the eggs of the worm in the stools of the patients.” Leiper records one case from Japan and one from China. The parasites occupy the middle third of the small intestine, and even when present in large numbers appear to be harmless.
This small species, according to Looss, frequently occurs in Egyptian dogs, less so in cats, and has also been found in the fox, as well as once in Milvus parasiticus; Janson also reports this species from the intestine of the dog in Japan.
Metagonimus, Katsurada, 1913; Yokogawa, Leiper, 1913.
Resembles in general structure Heterophyes. In the arrangement of its ventral genital suckers resembles but differs from that of Tocotrema,273 Looss. The ventral and genital suckers lie laterally and on the right.
Metagonimus yokogawai. Katsurada, 1913.
Syn.: Yokogawa yokogawai, Leiper, 1913.
Fig. 164.—Metagonimus yokogawai, Katsurada, 1913: the spines are only shown over a small part of the skin. (After Leiper.)
One to 1·5mm. long, seldom 2·5mm., and 0·4 to 0·7mm. broad; elliptical in shape. The body is thickly covered with nail-shaped spines about 10µ long. Oral sucker 77µ, to 85µ in diameter. Ventral sucker characteristic and peculiar 0·12 to 0·14mm. by 0·08 to 1mm. It is a sac-like organ placed deeply in the body, but does not open as in other flukes on the ventral surface. Testes elliptical, not quite symmetrically placed at the hind end of the body. Vesicula seminalis retort-shaped, situated transversely, internal to the ventral sucker. Pars prostatica present.
Habitat.—Mainly in upper or middle portion of jejunum, rarely in cÆcum. They penetrate deep into the mucosa, but not into the submucosa, and post mortem appear as a number of small brown points. They frequently occur in the solitary glands, which they destroy. They cause chronic catarrh of the gut. Parasitic in man and mammals.
Geographical Distribution.—Japan.
Life-history.—The cercarial stage occurs in a trout (Plecoglossus altivelis) and seldom in Crassius sp. and Cyprinus sp. Infection takes place through the eating of the fish raw. Seven to sixteen days later eggs appear in the fÆces (of dog).
Family. DicrocoeliidÆ, Odhner, 1910.
Genus. Dicrocoelium, Dujardin.
DicrocoeliidÆ, with leaf-shaped bodies, pointed posteriorly and anteriorly. Greatest width behind the mid-line. Vitellaria double. The testes smooth or indented, lying symmetrically or obliquely beside or behind the ventral sucker. The ovary approaches the median line behind one testis. Parasitic in the liver and gall-bladder (rarely in the intestine) of members of all classes of vertebrate animals—by preference in birds and mammals.
Dicrocoelium dendriticum, Rud., 1819.
Syn.: Dicrocoelium lanceatum, Stil. and Hass., 1896; Fasciola lanceolata, Rud., 1803 (nec Schrank, 1790); Distomum lanceolatum, Mehlis, 1825; Dicrocoelium lanceolatum, Dujardin, 1845.
Fig. 165.—Dicrocoelium dendriticum, Rud. V.s., ventral sucker; Cb., cirrus pouch; I., intestinal cÆca; V.sc., vitellaria; T., testicles; O., ovary; M.s., oral sucker; Ut., uterus. 15/1.
Body lancet-shaped, narrowing especially at the anterior extremity; length 8 to 10mm., breadth 1·5 to 2·5mm., the greatest breadth usually behind the middle of the body. Suckers distant from each other by about one-fifth the length of the body; oral sucker about 0·5mm., ventral sucker about 0·6mm. Pharynx globular, adjoining the oral sucker; oesophagus 0·6mm. in length; intestinal cÆca reach to four-fifths of the body length. Genital pore at the level of the bifurcation of the intestine; cirrus pouch small and slender. The large, slightly lobed testes lie obliquely one behind the other behind the ventral sucker; the ovary, which is considerably smaller, is placed behind the posterior one; the vitellaria, commencing at the level of the posterior testis, terminate far before the cÆca. The uterus, situated behind the ovary, extends throughout the posterior end, not confined to the central field, but overlapping the lateral fields with its transverse coils; at the posterior edge of the body it turns back again and winds forwards to the ovary in transverse loops, then between the testes, and finally, dorsal to the ventral sucker, terminates in the genital pore. The thick-shelled eggs when young are yellowish, when older dark brown. They measure 38µ to 45µ by 22µ to 30µ. They contain an oval or roundish miracidium, only the anterior part of which is ciliated, and which possesses a rudimentary intestinal sac with a boring spine. The miracidia do not hatch out in water spontaneously, but, according to Leuckart, in the intestines of slugs (Limax, Avion), but they do not develop either in these (slugs) or in water-snails.
The lancet fluke inhabits the biliary duct of herbivorous and omnivorous mammals (sheep, ox, goat, ass, horse, deer, hare, rabbit, pig), and is often found associated with the liver fluke; it is not, however, so common nor so widely disseminated, nevertheless, it has been met with outside of Europe, namely, in Algeria, Egypt, Siberia, Turkestan, and North and South America.
Fig. 166.—Eggs of Dicrocoelium dendriticum, Rud. To the left seen flat, to right lying on one side. 600/1.
Fig. 167.—Miracidia of Dicrocoelium dendriticum. a, from the dorsum; b, from the side. (After Leuckart.)
In man it is still more uncommon than the liver fluke, and has hitherto only been observed seven times (Germany, Bohemia, Italy, France, and Egypt); it may, however, have occurred more frequently, and have been overlooked, as in slight infections it produces no special symptoms.
The intermediate host is still unknown. Leuckart for some time held the opinion that small species of Planorbis from fresh water, which contain encysted Distomata, were to blame, and he supported his views by a feeding experiment which seemingly yielded positive results; this, however, is not definitely proved. Piana’s statement that small land snails are the intermediate hosts has also not been proved.
Fig. 168.—Echinostoma ilocanum. Vo., oral sucker; Ph., pharynx; Cirre, cirrus; V.v., ventral sucker; Ut., uterus; G.c., ovary; Ov., shell gland; T., testes; T.d., vitellarium; C.ex., excretory vesicle. (After Brumpt.)
Family. EchinostomidÆ, Looss, 1902.
Sub-family. EchinostominÆ, Looss, 1899.
Genus. Echinostoma, Rud. 1809; Dietz, 1910.
Fore-body not bulging. Greatest width at or behind the ventral sucker. Oral sucker not atrophied. Collar kidney-shaped with a double dorsally unbroken row of spines, terminating in four to five angle spines. The border spines of the aboral series not larger than the oral. Skin spined or smooth. Body elongated. Uterus long with numerous transverse coils. Ventral sucker in the anterior quarter of body. Cirrus sac small, almost completely in front of the ventral sucker. Testes round or oval, smooth incurved or lobed, in the hinder half of body. Ovary median or lateral in front of testes. Vitellaria from hinder margin of ventral sucker to end of body. Eggs oval, 84µ to 126µ by 48µ to 82µ.
The spines placed most ventrally, or those placed most medially on ventral surface, are from differences of position or form termed “angle” spines, the rest “border” spines.
Type.—Echinostoma echinatum, Rud.
Fig. 169.—Echinostoma ilocanum, Garrison, 1908: head end showing collar of spines, ventral view. (After Leiper.)
Echinostoma ilocanum, Garrison, 1908.
Length 4 to 5mm., breadth 1 to 1·35mm., thickness 0·5 to 0·6mm. The circum-oral disc 0·3mm. broad, separated by a shallow groove from the body. Crown of forty-nine spines and five to six angle spines on each side continuous with an irregularly alternating series of fourteen spines on the dorsum. Largest spines are 34µ long, 8µ thick at the base. The remainder of the dorsal spines are 24µ by 6µ. Skin thickly covered with scales on the margins of the body as far back as the level of the hind testis. Oral sucker, 0·18mm.; ventral sucker, 0·4 to 0·46mm. Its anterior border about 0·07mm. from the anterior end. Pharynx 0·17mm. long, 0·11mm. broad. Testes about mid-line of the body, much lobed; the lobes of the anterior testis run transversely, while the axis of the posterior testis is longitudinal, as often occurs in the EchinostomidÆ. Cirrus sac
Average.—99·5µ by 56µ.
Habitat.—Gut of man (Filipinos), Philippine Islands.
Echinostoma malayanum, Leiper, 1911.
Fig. 170.—Echinostoma malayanum, Leiper, 1912: anterior end showing collar of spines, ventral view. (After Leiper.)
Twelve millimetres long, 3mm. broad, 1·3mm. thick. Ends bluntly rounded. At the anterior end a ventral furrow on either side, one-third the width of the body, marking off the circum-oral collar. Along its edge is a row of forty-three spines extending across the middle line dorsally but not ventrally. The spines vary in size from 0·07mm. in length (ventrally) to 0·05 to 0·016mm. (dorsally). Cuticular spines also exist on the ventral side as far back as posterior end of body, but dorsally limited to a triangular area ending in front of the ventral sucker. Oral sucker 0·07mm. thick, occupying the middle
Habitat.—Gut of man (Tamils), Malay States.
Sub-family. HimasthlinÆ, Odhner, 1910.
Genus. Artyfechinostomum, Clayton-Lane, 1915.
Crown of thirty-nine spines, continuous over dorsum. Two corner spines long. Vitellaria extend from posterior margin of sucker to posterior end of fluke. Eggs without filament. [Although the possession of strong rose-thorn hooks is given by Odhner as a sub-family characteristic, yet in this genus assigned to this sub-family they have not been seen.—J.W.W.S.]
Artyfechinostomum sufrartyfex, Clayton-Lane, 1915.
Spirit specimens: 9 by 2·5 by 0·8mm. thick. Ventral sucker conspicuous, 1mm. in diameter. Cirrus sac 2mm. long. Testes lobed, about 1·5mm. in diameter. Posterior border of posterior testes 1mm. from posterior end. Vitellaria meet posteriorly behind the posterior testis.
Family. SchistosomidÆ, Looss, 1899.
Genus. Schistosoma, Weinl, 1858.
Syn.: GynÆcophorus, Dies., 1858; Bilharzia, Cobb., 1859; Thecosoma, Moq. Tandon, 1860.
Fig. 171.—Schistosoma hÆmatobium, Bil.: male carrying the female in the canalis gynÆcophorus. 12/1. (After Looss.)
Fig. 172.—Transverse section through a pair of Schistosoma hÆmatobium in copulÂ. In the male the point of reunion of the intestinal forks has been cut across. (After Leuckart.)
The males have bodies that widen out considerably behind the ventral sucker, the lateral parts of which in-roll ventrally, forming the almost completely closed canalis gynÆcophorus, within which the female is enclosed. There is no cirrus pouch. The male has five or six testes, the females are filiform; the uterus is long.
Schistosoma hÆmatobium, Bilharz, 1852.
Syn.: Distoma hÆmatobium, Bilh.; Distoma capense, Harley, 1864.
The Male is whitish, 12 to 14mm. in length, but is already mature when 4mm. long. The anterior end is 0·6mm. or a little over in length. The suckers are near each other, the oral sucker is infundibular, and the dorsal lip is longer than the ventral one. The ventral sucker is a little larger, 0·28mm., and is pedunculated. A little behind the ventral sucker the body broadens to a width of 1mm., decreasing, however, in thickness; the lateral edges in-roll ventrally, so that the posterior part of the body appears almost cylindrical, 0·4 to 0·5mm. in diameter; the posterior extremity is somewhat more attenuated. The dorsal surface of the posterior part of the body is covered with spinous papillÆ. There are delicate spines on the suckers, and larger ones invest the entire internal surface of the gynÆcophoric canal, as well as a longitudinal zone at the edge of that side of the external surface that is covered by the other side rolling over it. The oesophagus is beset with numerous glandular cells (fig.173), and presents two dilatations; the intestinal bifurcation is close in front of the ventral sucker, the two branches uniting sooner or later behind the testes into a median trunk, which may again divide at short intervals. The excretory pore is at the posterior end, but placed somewhat dorsally; the genital pore is at the beginning of the gynÆcophoric canal, thus
Fig. 173.—Anterior end of the male Schistosoma hÆmatobium, Bilh. V.s., ventral sucker; I., gut cÆca; G.p., genital pore; T., testes; O.s., oral sucker; Oe., oesophagus with glandular cells; V.s., vesicula seminalis. 40/1. (After Looss.)
The Female—filiform, about 20mm. in length, pointed at each end, and measuring 0·25mm. in diameter in the middle. Their colour varies according to the condition of the contents of the intestine. (Posteriorly they are dark brown or blackish.) The cuticle is smooth except in the sucker, where there are very delicate spines, and at the posterior end, where there are other larger spines. The oral sucker is a little larger than the pedunculated ventral sucker (0·07 and 0·059mm. respectively). The anterior part of the body, 0·2 to 0·3mm. in length; the oesophagus is as in the male. The intestinal bifurcation is in front of the ventral sucker, the two branches uniting behind the ovary and the trunk running in a zigzag manner to the posterior border. There are indications of diverticula at the flexures. The ovary is median. In young females it is of an elongated oval shape; in older females the posterior end becomes club-shaped, whereas the anterior end becomes attenuated; the oviduct originates at the posterior end, but immediately turns forwards and joins the parallel vitelline duct in front of the ovary (fig.174), where the shell gland cells open; the common canal becomes dilated to form the oÖtype, and then proceeds as the uterus, with only slight convolutions, along the central field to the genital pore, which lies in the middle line immediately behind the ventral sucker. The single vitellarium starts behind the ovary and extends to the posterior end. The acini are situated at the sides of the excretory duct, which runs a median course. The eggs are compact spindles, much dilated in the middle; they have no lid, and are provided with a terminal spine (rudimentary filament) at the posterior end, measuring 120µ to 150µ in length and 40µ to 60µ in breadth, but vary in size and shape (fig.175).
Fig. 174.—Schistosoma hÆmatobium, Bilh.: genitalia of the female. V.s., ventral sucker; I., gut cÆca; V.d., vitelline duct; V.sc., vitellarium; O., ovary; Oe., oesophagus; Sh., shell gland; U., uterus. Magnified. (After Leuckart.)
Distribution.—In order to understand the distribution of the worms and eggs in the body, it may be well to recall the blood supply of the abdominal and pelvic organs. It is generally assumed that the early life (? cercarial stage) of the worms occurs in the liver, and that the young worms travel from here, where they are invariably found, to their various sites along the portal vein and its tributaries and so against the blood stream. The tributaries of the portal vein are:—
(1) Superior mesenteric, the tributaries of which are: (a) the veins of the small intestine; (b) ileo-colic; (c) right colic; (d) middle colic; (e) right gastro-epiploic; and (f) inferior pancreatic. By these paths infection of the small intestine, ascending and transverse colon and pancreas would occur.
(2) Splenic. (Ova have been recorded by Symmers in the spleen.)
(3) Inferior mesenteric, the tributaries of which are (a) superior hÆmorrhoidal veins from the upper part of the hÆmorrhoidal plexus; (b) sigmoid veins from sigmoid flexure and lower portion of descending colon; (c) left colic vein draining descending colon.
The superior hÆmorrhoidal veins form a rich plexus in the rectum, and below this level in the upper and middle parts of the anal canal. The plexus forms two networks, an internal plexus in the submucosa and an external on the outer surface. The internal plexus opens at the anal orifice into: (a) branches of the inferior hÆmorrhoidal vein (from the pudic); (b) the external plexus. The external plexus gives off: (a) inferior hÆmorrhoidal opening into internal pudic (of internal iliac vein); (b) mid-hÆmorrhoidal into internal iliac or its branches; and (c) superior hÆmorrhoidal opening into inferior mesenteric. The external plexus further communicates with the vesico-prostatic plexus. The vesico-prostatic (vaginal) plexus opens into the vesical veins, which drain into the interior iliac vein. This plexus also receives afferents from the pudendal plexus, the chief tributary of which is the dorsal vein of the penis. The pudendal plexus also receives branches from the inferior pudic and the anterior surface of the bladder.
There is thus a communication between the portal vein and the vena cava by means of these plexuses, viz., through the inferior and middle hÆmorrhoidals, and by the inferior hÆmorrhoidals to the bladder and thence by the vesical veins or the pudic to the caval system (interior iliac).
It is thus by the inferior mesenteric and its tributaries that the worms reach the descending colon, rectum, anal canal, and eventually the bladder, and in some cases the caval system.
Before considering what is actually found post mortem in these veins and the organs drained by them, we may further recall the fact that the calibre of “medium” veins is 4 to 8mm., “small” veins
Liver and Portal Vein.—Here worms are most easily found post mortem. Often only males are found and these of the same size, and if females occur only a few worms are found in copulÂ. The worms are frequently not full size and the males may contain no free spermatozoa in their testes, and as regards the females some may be fertilized, others not, as shown by the presence or absence of spermatozoa in the seminal receptacle or uterus. In either case they may contain eggs—lateral-spined—usually one, less often two, but there may be as many as five or six. These eggs may also show some abnormality, which takes the form of: (1) abnormal contents, viz., disintegrating yolk cells with or without an ovarian cell; (2) abnormal shape but with normal contents and probably represented by the collapsed and empty egg-shells which are found in the tissues.
As to the interpretation of these facts, Looss believes that these lateral-spined eggs are products of young females whose egg-laying is not at first properly regulated. The shape that the eggs take, viz., with a lateral spine, is determined by an excess of material—ovarian and yolk cells—being present in the oÖtype. The shape of eggs depends upon the position they have in the oÖtype during their formation. In young females an excess of cells—yolk cells especially—accumulates, distending not only the dorsal wall but a portion also of the short duct joining the oÖtype to the uterus. The result of this is that the axis of the oÖtype and egg is almost transverse to the body, and the posterior funnel-shaped portion of the oÖtype, instead of being terminal, has now a lateral or rather a ventral position, so that the spine which occupies this portion, instead of being terminal, is now lateral. It is noteworthy that these lateral-spined eggs are thicker, owing to the excess of material present, and not uncommonly have a curved anterior border, due to a projection of the anterior end into the anterior opening of the oÖtype.
As these eggs are being laid by females in the portal vein they are carried back to the liver by the blood stream. The liver is one of the commonest sites for these eggs; also terminal-spined eggs may be found here for the same reason.
HÆmorrhoidal Veins.—Mature worms, generally in copulÂ, are usually found here, though young not fully grown females may also occur. The tissues of the rectal wall (or colon) show, as a rule, large quantities of lateral-spined eggs, though less often only terminal-spined eggs may be found.
Vesico-prostatic Plexus.—Worms in copul are found in the veins
The female worm is 280µ in diameter. Veins in the submucosa of the rectum less than 178µ in diameter are not affected with endophlebitis. It is probable that the female even by stretching could not penetrate much beyond this. Eggs are probably then laid in the submucosa as near the muscularis mucosa as possible. Now if the eggs are laid in a vein of larger calibre than the worm fills, the eggs would be carried back to the inferior mesenteric vein, so that presumably the worm must succeed in blocking the vein already narrowed by endophlebitis, so that by the stasis which ensues the eggs may escape from the veins. How this occurs is not exactly known; it is not necessarily due to the spine, as the same escape into the tissues occurs in spineless eggs, such as those of Schistosoma japonicum. The eggs, then, pass as foreign bodies through the tissues. Another hypothesis is that the worms leave the veins in order to lay their eggs, but the evidence is against this.
Caval System.—Occasionally worms that have passed through the vesical plexus may be found in the iliac vein, inferior vena cava, and even the lungs. If the worms are young they contain a lateral-spined egg; if adult, numerous (50 to 100) terminal-spined eggs.
Lungs.—When the liver is strongly infected with (terminal-spined) eggs it is possible that by passive movements some may pass into the intralobular veins, and thence by the inferior vena cava to the lungs.
Gall-bladder.—Similarly terminal-spined eggs pass into the bile-capillaries and gall-bladder (where they may be abundant), and so into the fÆces.
Detection of Eggs.—Occasionally eggs may be found in various other parts of the body. They are best detected by macerating pieces of the tissue in question in about 14 per cent. hydrochloric acid at 50 to 60°C. (Looss).
Pathological changes:—
Rectum.—These have been studied thoroughly by Letulle in the case of an apparently pure infection of the rectum.274 They take the form of a chronic diffuse inflammation, which may result in—(1) ulceration, or (2) hyperplasia of the mucosa, producing adenomata.
Ulcerative Form.—The mucosa is transformed into a mass of vascular connective tissue. The connective tissue spaces next become invaded by numerous mononuclear cells. The tissue itself
Hyperplastic Form.—The LieberkÜhn glands of the mucosa at first hypertrophy; then there is an actual hyperplasia resulting in adenomata. The interstitial tissue of the glands is also greatly hypertrophied, giving rise to very vascular granulations. These growths are often hollow and contain worms. Many eggs are found in the mucosa on their way to the lumen of the gut.
The muscularis mucosa is thickened up to twice or even ten times the normal. Its vessels are dilated (36µ to 80µ), but they do not allow of the passage of worms.
The submucosa is profoundly changed; rigid and hard instead of supple. It is here that the greatest number of eggs occur. A remarkable condition of endophlebitis exists in the veins of the submucosa, not only in the smaller ones but also in the larger ones (370µ by 270µ). This endophlebitis results in a more or less complete occlusion of the vessels of the lumen.
The muscular coats are free from change, also their veins.
The Serous Coats.—The veins about 1,900µ, also show endophlebitis. Besides the rectum, in extreme cases even the transverse colon, the cÆcum and small intestine may be affected.
Bladder.—In the early stages the mucosa is deep red and swollen like velvet, or there may be localized patches of hyperÆmia or extravasation. The subsequent changes take two chief forms:—
(1) Sandy Patches.—The mucosa looks as if it were impregnated with a fine brownish or yellowish powder (myriads of ova). This is accompanied by a gradual hypertrophy and new formation of connective tissue, so that dry, hard or plate-like patches with this sandy appearance arise; the thickening eventually affects all the coats of the bladder. In the older patches many of the eggs are calcified. These patches sooner or later break down, ulcerate and necrose. Phosphatic deposits are abundant and stone is common. These patches are not found in the rectum.
(2) Papillomata.—Where the inflammatory change produced by the eggs gives rise to hypertrophy and hyperplasia of the mucosa, papillomata result, the axis of which is formed by connective tissue of the submucosa. These are most variable in shape and form and bleed readily, and sometimes contain cavities of extravasated blood.
As in the rectum, it is in the submucosa that eggs are most abundant, and worms in copul occur in the veins of this layer, but endophlebitis is not as general as described in the rectum. Malignant disease of the bladder is not an uncommon sequela of bilharziasis.
Eggs also occur in the lymphatic glands of the gut.
Geographical Distribution.—East Africa: Nile Valley, Red Sea Coast, Zanzibar, Portuguese East Africa, Delagoa Bay, Natal, Port Elizabeth.
South Africa: Cape Colony, Orange Free State, Transvaal, Mauritius, Bourbon, Madagascar.
West Africa: Angola, Cameroons, Gold Coast, Gambia, Senegal, Sierra Leone, Lagos, Nigeria.
North Africa: Tripoli, Tunis, Algeria, parts of the Sahara.
Central Africa: Sudan, various portions. Uganda, Nyasaland.
It occurs with varying frequency in these regions. It is probably more widely spread than this list implies, as undoubtedly many cases are seen which are not recorded.
Isolated cases have been recorded from Arabia, India,275 Greece, Cyprus.
Fig. 175.—Ovum of Schistosoma hÆmatobium, Bilh., with miracidium, which has turned its anterior end towards the posterior end of the egg. 275/1. (After Looss.)
The means by which infection is brought about are still uncertain; we only know that the miracidia (fig.175) enclosed in the discharged eggs do not hatch if the eggs remain in the urine, but after cooling perish. As soon, however, as the urine is diluted with water the shell swells, generally bursting lengthways, and releases the miracidium from its investing membrane, so that it can swim about with the aid of its cilia. In its structure it differs but little from the miracidium of Fasciola hepatica, as, for instance, in the lack of eyes; the two large gland cells situated on either side of the intestinal sac are also present in the miracidia of Fasciola hepatica.
Sarcode Globules.—This is a term applied to certain globules which at times appear in the miracidium and are later ejected. Some authors
The Bilharzia mission, under R.T. Leiper, sent to Egypt by the War Office early in 1915, reports that cercariÆ of bilharzia type were recognized in four of the commonest fresh-water molluscs around Cairo.
With material obtained from naturally infected Planorbis boissyi acute bilharziosis was experimentally produced in rats, mice, and monkeys. Infection takes place experimentally through the skin and also through the mucous membrane of the mouth and oesophagus. The miracidium, after entering the mollusc, develops into a sporocyst. This gives rise not to rediÆ, but to secondary sporocysts, which, in turn, produce cercariÆ. These, like the adult worm, differ from other distomes in lacking a muscular pharynx.
Schistosoma mansoni, Sambon, 1907.
According to Manson, Sambon and others, the eggs with lateral spines belong to a species different from Schistosoma hÆmatobium. Infections with this species only are said to occur in the Congo, Southern States of North America, West Indies (Guadeloupe) and Brazil (Bahia). The following characters, according to Flu, differentiate this species: (1) In the male the transition from the anterior portion of the worm to the lateral fields (the infolded portions which form the gynÆcophoric canal) is not a gradual one as in Schistosoma hÆmatobium, but in this case the lateral fields rise suddenly, almost at right angles to the anterior portion. (2) The ovaries have a well-marked convoluted course as in no other schistosome. (3) The oÖtype is symmetrical in reference to the long axis of the body, its duct being lateral on the ventral side (Looss’ explanation of this we have already given). (4) The worms live exclusively in portal vein and tract. (As lateral-spined eggs occur also in the bladder, this is not exactly true.)
Schistosoma hÆmatobium, Bilharz, 1852.
Male, four or five large testes. Gut forks unite late, so that the single gut stem is short. Female, ovary in posterior half of body. Uterus very long, voluminous, with many terminal-spined eggs, some lying in pairs. Vitellaria in posterior fourth of body. CercariÆ in Bullinus contortus and Bullinus dybowski (syn.: Physa alexandrina) in Egypt.
Schistosoma mansoni, Sambon, 1907.
Male, eight small testes. Gut forks unite early, so that the single gut stem is very long. Females, ovary in anterior half of body. Uterus very short; usually only one lateral-spined egg at a time in utero. Vitellaria occupy posterior two-thirds of body. CercariÆ in Planorbis boissyi in Egypt.
The above morphological descriptions are founded on worms of each species, derived from experimentally infected mice (Leiper, R.T., Brit. Med. Journ., March 18, 1916, p.411).
Schistosoma japonicum, Katsurada, 1904.
Syn.: S. cattoi, Blanchard, 1905.
Fig. 176.—Schistosoma japonicum: anterior end with testes; posterior end with point of union of cÆca. Length of worm about 10mm. (After Katsurada.)
Male.—Eight to 19mm., but extreme limits are 5 to 22·5mm. Consists of a short fore-body, separated by the ventral sucker from the hind-body. The ventral sucker is stalked and somewhat larger than
Fig. 177.—Schistosoma japonicum, male and female in copulÂ. ×60. (After Katsurada.)
Female.—Up to 26mm., generally thinner than the male. Surface smooth. Suckers armed with fine spines. Ventral sucker larger than oral. Body thicker behind the region of the ovary. The gut forks unite immediately behind the ovary. The united gut much thicker than in S. hÆmatobium. Ovary elliptical, almost in the mid-body, its hinder portion dilated. The oviduct arises from its posterior end and then runs sinuously forward, where it is joined by the vitellarian duct; the vitellarium well developed, extending from behind the ovary almost but not quite to the posterior end as in S. hÆmatobium. Shell gland ducts enter at the junction point of oviduct and vitelline duct. The canal here forms an oÖtype and then proceeds as the uterus to open directly behind the ventral sucker. The uterus occupies almost half the hind-body. In S. hÆmatobium this is not so. The uterine canal is cleft-like, i.e., its dorso-ventral diameter is much greater than its lateral diameter. The number of eggs varies from about 50 to 300 from observations made in various hosts.
Eggs.—In utero assume various shapes, as they are soft; the lumen of the uterus is narrow. Outside they are oval, faint yellow, double
Fig. 178.—Schistosoma japonicum: eggs from human liver, showing “spines” and “hoods” at opposite pole. (After Looss.)
Fig. 179.—Schistosoma japonicum: from dog. Uterine egg. × c. 800. (After Katsurada.)
Mode of Infection.—The miracidia hatch in water in as little as fifteen minutes, but the majority in one to three hours. They will live in water for about twenty-four hours. In water they undergo a transformation into “larvÆ,” which then penetrate the skin, as has been shown by Japanese writers to hold good for man, cattle, dog and cat. The penetration of the skin is attended with an eruption on the legs, “Kabure.” The exact route by which the worms reach the portal vein is uncertain. Infection in Japan takes place from spring to autumn, especially May to July, when the soil is contaminated with manure of cattle infected with S. japonicum. They also appear to develop in molluscs. Leiper and Atkinson found cercariÆ (in sporocysts)
Habitat.—The worm occurs in Japan, China, and the Philippines. The normal host is man and mammals. Cattle, dog and cat are often found naturally infected. Mice can also be experimentally infected. Their seat of election is the portal vein and its branches, especially the mesenteric veins. They either swim free in the blood or remain fixed by their suckers to the intima of the vessels. They have also been found in the vena cava and right heart of a cat, but not so far in the vesical plexus.
Fig. 180.—Schistosoma japonicum: from dog. × c. 800. (After Katsurada.)
Fig. 181.—Schistosoma japonicum: from dog. Egg from fÆces. × c. 800. (After Katsurada.)
Eggs are found in the submucosa and mucosa of the gut, especially the colon, and at times in the serosa and subserosa of the small intestine, where they give rise to new growths. Occasionally eggs are found in the brain. The life of the worms is at least two years.
Pathogenic Effects.—AnÆmia through loss of blood due to worms; enlarged spleen, toxic in origin (?); phlebitis, thrombosis, due to portal stasis; the eggs, however, cause the greatest mischief. They are carried by the circulation to various
Liver.—The eggs reaching this organ give rise to granulomata and hence enlarged liver, and later, when connective tissue is formed, to contraction. The surface is rough and irregularly granular, “parasitic embolic cirrhosis” of Yamagiwa.
Fig. 182.—Schistosoma japonicum: section through the gut of a Chinaman showing eggs. ×58. (After Catto.)
Gut.—The eggs in the mucosa and submucosa cause catarrh and destruction of tissue or new growth. In the small intestine the eggs are mainly in the serosa and subserosa, where they give rise to polypoid or branched growths.
Spleen.—Enlarged, at first due to toxin (?) and later due to portal stasis. Eggs in the spleen are uncommon.
Ascites also arises from the portal stasis, and is generally present in advanced cases.
Eggs may be found in many other situations: glands (numerous), mesentery, stomach, pancreas, kidney, etc. The bladder remains free.
Fig. 183.—Schistosoma japonicum: liver showing eggs in the intra- and interlobular connective tissue. × c. 80. (After Katsurada.)
Class III. CESTODA, Rud., 1808.
Tapeworms have been known from ancient times—at all events, the large species inhabiting the intestines of man—and there has never been a doubt as to their animal nature. The large cysticerci of the domestic animals (occasionally of man also) have been known for an equally long period, but they were generally regarded as growths, or “hydatids,” until almost simultaneously Redi in Italy, and Hartmann and Wepfer in Germany, concluded from their movements and organization that they were of animal nature. From that time the cysticerci have been included amongst the other intestinal worms, and Zeder (1800) established a special class (Cystici, Rud., 1808) for the bladder worms. Things remained in this condition until the middle of the last century, when KÜchenmeister, by means of successful feeding experiments, demonstrated that the cysticerci were definite stages of development of certain tapeworms. Before KÜchenmeister, E. Blanchard, van Beneden, and v. Siebold had held the same opinion in regard to other asexual Cestodes.
Since the most remote period another question has again and again occupied the attention of naturalists, the question of the morphological nature—that of the INDIVIDUALITY OF THE TAPEWORM. The ancients, who were well acquainted with the proglottids (Vermes cucurbitani) that are frequently evacuated, were of the opinion that the tapeworm originated through the union of these separate proglottids, and this view was maintained until the end of the seventeenth century. In 1683 Tyson discovered the head with the double circlet of hooks in a large tapeworm of the dog; Redi (1684) was also acquainted with the head and the suckers of several TÆniÆ. Andry (1700) found the head of TÆnia saginata, and Bonnet (1777) and Gleichen-Rusworm (1779) found the head of Dibothriocephalus latus. Consequently most authors, on the ground of this discovery, considered the tapeworm as a single animal, that maintains its hold in the intestine by means of the head, and likewise feeds itself through it. The fact was recognized that there were longitudinal canals running through the entire length of the worm, and it was thought that these originated in the suckers, and that the entire apparatus was an intestine. As, moreover, the segments form at the neck, and are cast off from the opposite extremity, the tapeworm was also compared with the polyps, which were formerly regarded as independent beings.
Steenstrup, in his celebrated work on the alternation of generations (1841), was the first to give another explanation. This has been elaborated still further by van Beneden, v. Siebold and Leuckart, and until a few years ago all authorities adopted his views. According to this view, the tapeworm is composed of numerous individuals, something like a polyp colony, and, in addition to the proglottids—the sexual individuals which are usually present in large numbers—there is ONE individual of different structure, the scolex, which not only fastens the entire colony to the intestine, but actually produces this colony from itself, and therefore is present earlier than the proglottids. The scolex is a “nurse,” which, though itself produced by sexual means, increases asexually like a Scyphistoma polyp; the tapeworm chain has therefore been termed a strobila. Consequently the development of the tapeworms was explained by an alternation of generations. In support of this opinion it was demonstrated not only that the adult sexual creatures, the proglottids, can separate from the colony and live independently for a time, but that in certain TÆniÆ, and especially in many Cestodes of the shark, the proglottids detach themselves long before they have attained their ultimate size, and thus separated continue to develop, grow and finally multiply; the scolex also exhibits a certain independence in so far as, though not, as a rule, capable of a free life, yet it in some cases lives as a free being, partly on the surface of the body of marine fishes and partly in the sea. With the more intimate knowledge of the development of the cysticerci, the independent nature of the scolex was recognized. It is formed by a budding of the bladder that has developed from the oncosphere, in some cases (Coenurus) in large numbers, in other cases (Echinococcus) only after the parent cyst has developed several daughter cysts. Released from its mother cyst and placed in suitable conditions, it goes on living, and gives rise at its posterior end by budding to the strobila, the proglottids of which eventually become sexual individuals.
In order to make this clearer we will briefly summarize what takes place in the jelly-fishes.
By metamorphosis is meant a developmental change in the same individual, while alternation of generations, or metagenesis, implies a stage in which reproduction of individuals takes place by a process of budding or fission. This asexual reproductive stage alternates with the sexual mode of reproduction. Thus in the development of the Scyphozoa (jelly-fishes) we have:—
(1) The fertilized egg cell divides regularly and forms a morula.
(2) By accumulation of fluid in the interior this becomes a closed sac with a wall formed of a single layer of cells, forming the blastosphere or blastula.
(3) One end of the sac is invaginated, forming a gastrula.
(4) The gastrula pore or mouth closes, forming again a sac, the walls of which have two layers, forming a planula.
(5) This becomes fixed to a rock, an invagination forms at one end, a depression—the stomodÆum—communicating with the enteric cavity. Tentacles grow out and we have a ScyphozoÖn polype, Scyphistoma or Scyphula. It is to this stage that Steenstrup gave the name “nurse” (“wet-nurse”), because it nourished or produced asexually the succeeding forms.
(6) Asexual reproduction by transverse fission occurs in this, forming a pile of saucer- or pine-cone-like animals which before this time had been considered to be a distinct animal, which was called strobila from its resemblance to a pine-cone. This is the alternate generation.
(7) The individuals of the strobila become free and are called EphyrulÆ.
(8) These develop finally into adult sexual jelly-fish, Scyphozoa, so that comparing a tapeworm with this we have (a) egg, (b) scolex (= Scyphula or “nurse”), (c) asexual reproduction of the tapeworm chain (= strobila), (d) development of the individuals of the chain (proglottids) into sexual adults.
Van Beneden’s terminology for these stages is the following: Ciliated embryo = protoscolex; scyphistoma = deutoscolex (or scolex); free Ephyrula = proglottis. According to this view, as is the case in many endoparasitic Trematodes, asexual reproduction by budding occurs at two stages of the whole cycle of development, viz. (1) in the formation of the scolex by budding from the bladder (“nurse”), (2) in the formation of the strobila by budding from the scolex (“nurse”).
But in cysticercal larval forms it appears that the scolex does not arise in this way but is simply a part of the proscolex (hexacanth embryo), becoming invaginated into it for protection, so that there is no asexual gemmation here. It has been questioned also whether the strobila also arises by gemmation. If it does, the tapeworm is a colony of zoÖids produced by budding from the asexual scolex; if it is not produced in this way, then the tapeworm is to be regarded as an individual in which growth is accompanied by segmentation. Against the “colony” view are the facts that the muscular, nervous, and excretory systems are continuous throughout the worm, and that some tapeworms, such as Ligula, are unsegmented.
Finally, if the tapeworm is an individual the question arises which is the head end. As new segments are formed at the neck, and as this point in annelids is the antepenultimate segment, the scolex must be the last or posterior segment. The caudal vesicle or bladder of larval forms is consequently anterior. According to this view, in tapeworms as among many endoparasitic flukes, an asexual multiplication occurs at two points of the whole cycle of development, which is as follows: (1) egg, (2) oncosphere or hexacanth embryo, (3) bladder (cysticercus or hydatid), (4) (after digestion of the bladder) by budding, the scolex, (5) by budding from the scolex the sexual proglottids, (6) the egg; (4) and (5) being the two asexual stages.
Anatomy of the Cestoda.
If we except the tapeworms with only one proglottis, the Cestoidea Monozoa, Lang = Cestodaria, Monticelli, we can always distinguish in the Cestodes, in the narrower sense, one scolex or head and a large or small number of segments (proglottids). The SCOLEX serves the entire tapeworm for fastening it to the internal surface of the
The thickened part of the scolex that carries the suckers is usually called the head; the following flat (unsegmented) part connecting it with the proglottids is called the neck, and is sometimes quite small. In a few cases the entire scolex (or head) disappears, and its function is then undertaken by the contiguous portion of the chain of proglottids, which is transformed into a variously shaped PSEUDO-SCOLEX.
The proglottids are joined to the scolex in a longitudinal row, and are arranged according to age in such a manner that the oldest proglottis is farthest from the scolex, and the youngest nearest to it.
The number of segments varies, according to the species, from only a few to several thousands; they are either quadrangular or rectangular; in the latter case their longitudinal axis falls either longitudinal or transverse to that of the entire chain, according as the segments are longer than broad or broader than long. When the number of segments is very large, the youngest ones are, as a rule, transversely oblong, the middle ones are squarish, and the mature ones longitudinally oblong. The posterior border of the segments, as a rule, carries a longitudinal groove for the reception of the shorter anterior border of the following proglottis. The two lateral borders of the segment are rectilinear, but converge more or less towards the front, or they are bent outwards. In most of the Cestodes the segments, just as the neck, are very flat; in rare cases their
The first proglottis formed, and which in a complete tapeworm [i.e., sexually complete] is the most posterior, is as a rule smaller and of different shape, it also frequently remains sterile, as likewise happens in the next (younger) segments in a few species; otherwise, however, sooner or later the generative organs develop in all the segments, mostly singly, sometimes in pairs; in the latter case they may be quite distinct from each other or possess some parts in common. The term “mature” is used for a proglottid that has the sexual organs fully developed, while “gravid” is used for one containing eggs. Most of the species combine male and female genitalia in the same segment, only a few are sexually distinct (Dioecocestus). In the hermaphrodite species one male and one female sexual orifice are always present, and, in addition, there may be a second female orifice, the uterine opening; as a rule, however, this is lacking, and in one sub-family, the AcoleinÆ, to which also the genus Dioecocestus belongs, the other sexual orifice, the opening of the vagina, is also absent. The position of these orifices varies; the cirrus and vagina usually open into a common atrium on one lateral border or on a surface of the segments; the orifice of the uterus may be on the same surface or on the opposite one.
The surface on which the uterus opens is termed the VENTRAL SURFACE; if this orifice is absent, one must depend on the ovary, which almost always approaches one of the two surfaces; this surface is then called the ventral.
The length of the Cestodes—independently of their age—depends on the number and size of the segments, as well as on their contraction; the smallest species (Davainea proglottina) is 0·5 to 1·0mm. in length; the largest may attain a length of 10m., and even more.
The entire superficial surface of the tapeworms is covered with a fairly resistant and elastic layer, which exhibits several indistinctly limited layers and which is usually called a cuticle, which also covers the suckers, and is reflected inwardly at the sexual orifices. In some species fine hairs appear, either on the entire body or only in the region of the neck, on the external surface. In the cuticle there can be
Fig. 184.—Schematic representation of a small part of a transverse section of Ligula sp. Bs., basal membrane; Cu., cuticle; at its base are the endplates of the subcuticular (epithelial) cells; in the centre a cuticular sense organ, O.s.; F.v.s., vitelline follicle; Exc., excretory vessel; C., calcareous corpuscle; L.m., longitudinal muscles; M.c., myoblast; P.m., parenchymatous or dorso-ventral muscles; Pl., plexus of nerve fibres; A.m., circular muscles; Sc.c., subcuticular or matrix cell; T.c., terminal flame cell. 500/1. (After Blochmann.)
In addition to the above mentioned, there are other cuticular formations occurring on the cuticle of some Cestodes, such as immobile hairs and variously formed hooks, such as are seen principally on the scolex. Their development is only roughly known in a few species; they are usually already present in the larval stage, and of the same arrangement and shape as in the fully developed tapeworms; a matter of importance, because by these structures larvÆ can be recognized as being those of a certain species of tapeworm.
The CUTICULAR GLANDS in Cestodes are scarce.
The PARENCHYMA forms the chief tissue of the entire body, and in all essentials its structure is similar to that of the Trematodes.
The same doubt exists here also as to the nature of the parenchyma. Recent authors consider that it consists of highly branched cells, the processes of which ramify in all directions. These cells lie in a non-cellular matrix containing fluid vacuoles. This matrix spreads in between and so breaks the continuity of the epidermal cells.
In the parenchyma of almost all the Cestodes there are found in adult specimens, as well as in larvÆ, light-refracting concentrically striated structures, of a spherical or broad elliptical shape, which, on account of their containing carbonate of lime, are termed CALCAREOUS CORPUSCLES (fig.184, C.). Their size, between 3µ and 30µ, varies according to the species; their frequency and distribution in the parenchyma also varies, but they are chiefly found in the cortical layer. They are the product of certain parenchymatous cells, in the interior of which they lie like a fat globule in a fat cell, but according to others they are intercellular in origin.
The MUSCULAR SYSTEM of the proglottids is composed of—(1) the subcuticular muscles (figs.184 and 185), as a rule consisting of a single layer of annular muscles; (2) longitudinal muscles; (3) dorso-ventral fibres extending singly from one surface to the other, and at both ends expanding in a brush-like manner, and inserted into the basal membrane, consisting of an outer, more numerous, and an inner, less numerous but more powerful layer (the number of bundles in this layer being in certain cases of specific importance); (4) transverse fibres, the elements of which penetrate to the borders of the segments, thus passing through the longitudinal muscles and reaching
Fig. 185.—Half of a transverse section through a proglottis of TÆnia crassicollis. Cu., cuticle; Ex.v., external excretory vessel, to the right of which there is the smaller internal one; T., testicular vesicles; L.m., longitudinal muscles (outer and inner); M.f., lateral nerve with the two accessory nerves; Sc.c., subcuticular matrix cells; Sm.f., submedian nerve; Tr.m., transverse muscles; Ut., the uterus, and the middle of the entire transverse section. 44/1.
The mass of parenchyma bounded by the transverse muscles is termed the MEDULLARY layer, while the mass lying outside them is termed the CORTICAL LAYER.
It was known long ago that the myoblasts adhere to the dorso-ventral fibres as thickenings, but it is only recently that large star-shaped cells (fig.184), separated from but connected with them by processes, have been recognized as the myoblasts of other fibres (Blochmann, Zernecke).
Within the scolex the direction and course of the muscular layers change.
Fig. 186.—Dipylidium caninum: from the cat. In the upper figure the rostellum is retracted, in the lower protruded, a, sucker; b, hooks of rostellum; B, enlarged hook; c, apical aperture on scolex; d, longitudinal muscles; e, circular muscles. (After Benham.)
The SUCKERS are parts of the musculature, locally transformed, with a powerful development of the dorso-ventral muscles, now become radial fibres.
The ROSTELLUM of the armed TÆniÆ, like the proboscis of the RhynchobothriidÆ, also belongs to the same category of organs.
In the simplest form, the rostellum, or top of the head (as in Dipylidium caninum), appears as a hollow oval sac, the anterior part of which, projecting beyond the upper surface of the head, carries several rows of hooks (fig.186). The entire internal space of the sac is occupied by an elastic, slightly fibrous mass, while the anterior half of the surface of the rostellum is covered by longitudinal fibres and the posterior half by circular fibres. On contraction of the latter the entire mass is protruded through the apical aperture, the surface of the rostellum becomes more arched, and the position of the hooks is, in consequence, altered. The rostellum of the large-hooked TÆniidÆ, which inhabit the intestine of man and beasts of prey, is of a far more complicated structure, for, in addition to the somewhat lens-shaped rostellum carrying the hooks on its outer surface, there are secondary muscles grouped in a cup-like manner (fig.187). Every change in the curvature of the surface of the rostellum induces an alteration in the position of the hooks. In the hookless TÆniidÆ the muscular system of the rostellum is altered in a very different manner; in a few forms a typical sucker appears in its place.
Fig. 187.—Longitudinal section of the head and neck of TÆnia crassicollis, showing the lens-shaped muscular rostellum, with two hooks lying in the concentric cup-like mass of muscles. L.m., longitudinal muscles of the neck; L.f., left lateral nerve; G., ganglion; S.c., subcuticular layer; W1, external, W2, internal excretory vessel. 30/1.
The NERVOUS SYSTEM commences in the scolex and runs through
Fig. 188.—TÆnia coenurus, head and part of neck showing nervous system. Enlarged. (After Niemiec.)
The peripheral nerves arise from the nerve bundles as well as from the commissures situated in the scolex; some go direct to the muscles, while others form a close plexus of nerves external to the inner longitudinal muscles, which plexus likewise sends out fibres to the muscles, but principally to numerous fusiform sense organs
The EXCRETORY APPARATUS of the Cestodes is similar to that of other flat worms. The terminal (flame) cells, which hardly differ in appearance from those of the Trematodes, are distributed throughout the parenchyma, but are more common in the cortical than in the medullary layer (fig.184, T.c.). Before opening into a collecting tube, the capillaries run straight, tortuously, or in convolutions, anastomosing frequently with one another or forming a rete mirabile. The collecting tubes, which have their own epithelial and cuticular wall, and which also appear to be provided with muscular fibres, occur typically as four canals passing through the entire length of the worm (fig.189); they lie side by side, two (a wider thin-walled ventral, and a narrower thick-walled dorsal one) in either lateral field; in the head the two vessels on each side unite by means of a loop, at the posterior extremity they open into a short pyriform or fusiform terminal bladder which discharges in the middle of the posterior edge of the original terminal proglottis.
This primitive type (fig.189) of arrangement of collective tubes is subject to variation in most Cestodes, in the scolex as well as in the segments. Indeed, even the lumen of the four longitudinal tubes does not remain equal, as the dorsal or external tubes are more fully developed and become thicker, whereas the ventral or internal ones remain thin, and in some species quite disappear in the older segments (figs.185, 187). Moreover, very frequently connections are established between the right and left longitudinal branches, as in the head, where a “frontal anastomosis” develops, which in the TÆniidÆ usually takes the form of a ring encircling the rostellum (fig.190), and in the segments of a transverse anastomosis at each posterior border,
Fig. 189.—Young Acanthobothrium coronatum, v. Ben., with the excretory vessels outlined. Slightly enlarged. (After Pintner.)
Fig. 190.—Scolex of a cysticercoid from Arion sp., with the excretory vessels outlined. (After Pintner.)
The so-called “island” formation is another modification, i.e., at any spot a vessel may divide and after a longer or shorter course the two branches reunite, and this may appear in the collecting tubes themselves as well as in their anastomoses. The above-mentioned ring in the frontal commissure of the TÆniidÆ is such an island; similar rings also frequently encircle the suckers (fig.190). In extreme cases (TriÆnophorus, Ligula, Dibothriocephalus, etc.) this island formation extends to all the collecting tubes and their anastomoses. Instead of two or four longitudinal canals only, connected by transverse anastomoses at the posterior border of the segments, there is an irregular network of vessels, situated in the cortical layer, from which the longitudinal branches, having again subdivided, can only be distinguished at intervals, and even then not in their usual number.
The opening of the longitudinal branches at the posterior end requires more accurate investigation; it is true that a single terminal bladder is mentioned as being present in many species, but this is also disputed; when the original end proglottis has been cast off, the longitudinal branches discharge separately. Some species possess the so-called foramina secundaria, which serve as outlets for the collecting tubes; they are generally at the neck, but may be situated on the segments.
The contents of the excretory vessels is a clear fluid, the regurgitation of which is prevented by the valves present at the points of origin of the transverse anastomoses. The fluid contains in solution a substance similar to guanine and xanthine.
Genital Organs.—With the exception of one genus (Dioecocestus, Fuhrm.), in which the species are sexually differentiated, all the Cestodes are hermaphroditic; the genitalia develop gradually in the segments (never in the scolex), the male organs, as is usual in hermaphroditic animals, forming earlier than the female. The youngest proglottids generally do not exhibit even traces of genitalia: these, as a rule, develop first in the older segments, and the development proceeds onwards from segment to segment. In a few exceptional cases (Ligula) the sexual organs are already developed in the larval stage, but are only functional after the entry of the parasite into the final host.
Fig. 191.—Proglottis of TÆnia saginata, Goeze, showing genitalia. C., transverse excretory canal; N., lateral longitudinal nerve; W., longitudinal excretory canal; T., testicles scattered throughout the proglottis; Ut., opposite the central uterine stem (a closed sac); Ss., genital pore leading into the genital sinus; above the cirrus and coiled vas deferens (V.d.), below the vagina (Vag.), bearing near its termination a dilatation, the seminal receptacle; Vsc., the triangular vitellarium, and above it (Shg.) the shell gland; leading from this to the uterus is seen the short uterine canal, on either side of this the two lobes of the ovary (Ov.). 10/1.
With the exception of the end portions of the vagina, cirrus and uterus, all the parts of the genital apparatus lie in the medullary layer, except only the vitellaria, which in many species are in the cortical layer. The male apparatus consists of the testes, of which, as a rule, there are a large number,278 and which lie dorsal to the median plane (fig.185, T.); a vas efferens arises from each testis, unites with
Fig. 192.—Dibothriocephalus latus. Upper figure: female genitalia, ventral view. Lower figure: male genitalia, dorsal view. The central portion only of the proglottis is shown. a, cirrus sac; b, partly everted cirrus; c, genital atrium and pore; d, vaginal pore; e, uterus; f, uterine pore; g, vagina; h, ovary; i, shell gland; j, vitelline duct; k, lateral nerve; l, vitellarium; n, vas deferens (muscular portion); p, vas deferens; q, seminal vesicle; r and x, vasa efferentia; s, lateral excretory canal; t, testicular follicles. (After Benham and Sommer and Landois.)
The male sexual orifice almost always opens with that of the vagina into a genital atrium, the raised border of which rises above the edge of the segment and forms the genital papilla (fig.191).
Fig. 193.—Diagram of genitalia of a Cestode. g.p., genital pore; ? ?, male and female ducts opening into genital sinus; c.s., cirrus sac; v.d., coiled vas deferens (“outer seminal vesicle”); vag., vagina; sem. rec., seminal receptacle; sp. d., spermatic duct; C.c., fertilization canal; vit. d., vitelline duct; sh. g., shell gland; ut. c., uterine canal; ut., uterus; Ov., ovary; p, pumping organ. Cf. figs.191 and 233. (Stephens.)
The vagina, like the vas deferens, usually runs inwardly and posteriorly, where it forms a spindle-shaped dilatation (receptaculum seminis); its continuation, the spermatic duct, unites with the oviduct, the common duct of the ovaries (fig.191). The ovaries, usually two in number, are compound tubular glands in the posterior half of the proglottis, which extend into the medullary layer, but ventral to the median plane.
At the origin of the oviduct there is frequently a dilatation provided with circular muscles (suction apparatus), which receives the ovarian cells and propels them forward. After the oviduct has received the spermatic duct the canal proceeds as the fertilization canal, and after a very short course receives the vitelline duct or ducts, and then the numerous ducts of the shell glands (oÖtype). [Although the nomenclature of these parts varies, we may consider the oviduct as extending from the ovary to the shell gland and as receiving the spermatic duct and then the vitelline duct and the ducts of the shell gland. The short piece into which the shell gland ducts open corresponds to the oÖtype in the flukes, but in the tapeworms this portion of the canal is seldom dilated. From this point
Fig. 194.—Part of a transverse section through a proglottis of Dibothriocephalus latus. Ct., cuticle; C., cirrus; Vvs., vitelline follicles; L.M., longitudinal muscles; T., testicles; M., medullary nerve; S.c., subcuticle; T.m., transverse muscles; Ut., uterus. 20/1.
The egg cell that has been fertilized and supplied with yolk cells receives the shell material at the point of entry of the shell gland ducts, and, as a complete egg, then moves onward to the uterus. In those cases in which the uterus in its further course presents a convoluted canal, and may form a rosette (pseudo-phyllidea), there is an external opening which is usually separate from the genital pore, and lies on the same or the opposite surface. In all other cases, however, the uterus terminates blindly and is represented by a longer or shorter sac lying in the longitudinal axis (fig.191), but in many forms transversely. With the accumulation of eggs it becomes modified in various ways: (1) it sends out lateral branches (fig.241), or (2) forms numerous isolated sacs (PARENCHYMAL CAPSULES) containing single eggs or groups of eggs (fig.217); further, (3) in some cases at the blind end one or more special thick-walled cavities are formed (PARUTERINE ORGANS or UTERINE CAPSULES), in which all or most of the eggs are collected, the uterus then undergoing atrophy.
In species in which the uterus lacks an opening, simultaneously with the growth of this organ an atrophy of the male apparatus, at least of the testes and their excretory ducts, takes place; this atrophy also frequently occurs in the female glands, so that the entire mature segments have besides the uterus only traces of the genitalia left.
In the AcoleÏnÆ the vagina is more or less extensively atrophied, and in any case has no external opening.
A number of genera are distinguished by the duplication of the genitalia in every segment; the genital apparatus in its entirety, or with the exception of the uterus, is double, or the genital glands and the uterus are single, but the cirrus, vas deferens and vagina are double.
On comparing the genitalia of the Trematodes and Cestodes the parts will be found to agree, but the vagina of the Cestodes corresponds with the uterus of the Trematodes, and the uterus of the tapeworms to Laurer’s canal of the Trematodes, which in most of the Cestodes has lost its external orifice.
Development of the Tapeworms.
Copulation.—As each proglottis possesses its own genital apparatus, and male as well as female organs are present, the following processes may occur: (1) self- or auto-fecundation (without immissio cirri); (2) self- or auto-copulation (with immissio cirri); (3) cross-copulation between proglottids of the same or different chains (of the same species); and (4) cross-copulation in the same proglottis in species with double genital pores. These various modes have actually been observed.
In those species which lack the vagina (AcoleÏnÆ) it appears that the cirri, which are always furnished with hooks, are driven into the tissues and for the most part reach the receptaculum seminis.
The eggs of all Cestodes are provided with shells, but the shells, like their contents, vary. In genera that possess a uterine pore the mature eggs frequently do not differ from those of the Distomata; they have a brown or yellow shell of oval form provided with an operculum, and contain a number of yolk cells in addition to the fertilized ovarian cell (fig.128), but in other genera (with a uterine pore) the lid is absent and the egg-shell is very thin, the eggs of these genera resembling those of Cestodes in which the secretion of the vitellarium is a light albumin-like substance that contains only a few granules, and in which the egg-shell is very delicate and without operculum.
The eggs of TÆniidÆ, for example, at first consist of egg-shell (oÖtype), ovum and yolk cells. The egg-shell is as a rule soft, colourless and frequently deciduous, and the yolk is scanty in amount and contains few granules. The eggs are, moreover, more complicated than this. They enlarge and change their shape and various envelopes are developed around the embryo. The egg-shell proper often disappears, and one or more embryonal envelopes, or protoplasmic
Fig. 195.—Egg of Diplogonoporus grandis, showing the morula surrounded by yolk cells and granules. 440/1. (After Kurimoto.)
Fig. 196.—Uterine egg of TÆnia saginata, G. Uterine shell with filaments; the oncosphere with embryonal shell (embryophore) in the centre. 500/1. (After Leuckart.)
The embryonal development in most species takes place during the stay of the eggs in the uterus; in other species it takes place after the eggs have been deposited and are in water. Separate cells or a layer of cells always separate from the segmentation cells, as well as from the cells of the developing embryo, and form one or more envelopes round the embryo; usually two such envelopes are formed, the inner one of which stands in intimate relationship with the embryo itself and is often erroneously termed the egg-shell, but more correctly the embryonal shell or embryophore. In some species it carries long cilia, as in Dibothriocephalus latus, by aid of which the young swim about when released from the egg-shell; as a general rule, however, there are no cilia and this envelope is homogeneous, or is composed of numerous rods and is calcified, as in TÆnia spp. (fig.197). The second outer envelope (“yolk envelope”) (fig.207, 3) lies close within the true (oÖtype) egg-shell, and remains within it when the embryo hatches out, and in many species, as in TÆnia spp., it perishes at the end of the embryonal development with the delicate egg-shell which was formed in the oÖtype, so that one observes not the entire egg with egg-shell but only the embryo in its embryonal shell, viz., the embryophore (fig.197, a.).
Fig. 197.—a., oncosphere, in its radially striated embryophore (erroneously termed egg-shell) of TÆnia africana. Greatly magnified. (After von Linstow.) b., freed oncosphere of Dipylidium caninum. (After Grassi and Rovelli.) Both oncospheres show six spines.
The embryo (the ONCOSPHERE) enclosed within the embryonal shell (embryophore) is of spheroidal or ovoid form (fig.197, b.), and is distinguished by the possession of three pairs of spines, a few terminal (flame) cells of the excretory system, and muscles to move the spines.
No further development of the oncosphere takes place, either in the parent organism or in the open; in fact, in all cases in which the oncospheres are already formed within the proglottids they do not become free, but remain in their shell; it is only when the oncospheres are provided with a ciliated embryophore that they leave the egg-shell, and they even cast this ciliated envelope after having
In other cases, e.g., Hymenolepis spp., the uterine (oÖtype) shell persists in fÆces (fig.230).
In any case the oncospheres must be transmitted into suitable animals to effect their further development; in only very rare cases might an active invasion be possible, as, for instance, takes place with the miracidia of many Trematodes. The entry into an animal is, as a rule, entirely passive, that is to say, the oncospheres are swallowed with the food or water. Many animals are coprophagous and ingest the oncospheres direct with the fÆces; others swallow them with water, mud, or food contaminated by such fÆces. Infection is easily produced artificially by feeding suitable animals with mature proglottids of certain Cestodes or introducing the oncospheres with the food. As the mature tapeworm frequently finds the conditions suitable for its development in only one species of host, or in species nearly related, and perishes when artificially introduced into other hosts, experiment has taught us that to succeed in cultivating the oncospheres certain species of animals are necessary. Thus we are aware that the oncospheres of TÆnia solium, which lives in the intestine of man, develop only in the pig, and only quite exceptionally develop into the stage characteristic of all Cestodes—the cysticercus in the wide sense of the word—in a few other mammals. The oncospheres of T. saginata develop further only in the ox; those of T. marginata (of the dog) in the pig, goat, and sheep; those of T. serrata (of the dog) in hares and rabbits; those of Dipylidium caninum (of the dog and cat) in parasitic insects of the dog and cat, etc. It is not unusual that young animals
Once introduced into a suitable animal, which is only exceptionally the same individual or belongs to the same species as the one which harbours the adult tapeworm, the oncosphere passes into the larval stage common to all Cestodes, but varying in structure according to the species. In the simplest case—as, e.g., in Dibothriocephalus—such a larva resembles the scolex of the corresponding tapeworm, only that the head, provided with suckers, is retracted within the fore-part of the neck. Such a larval form is known as a plerocercoid (p??e???, full; ??????, tail). They differ from the cysticercoids in being solid larval forms, elongated, tape-like or oval, with the head invaginated. The conditions appear to be similar in Ligula, Schistocephalus, TriÆnophorus, but here the larvÆ are very large, indeed as large in the first-mentioned genera as the tapeworms originating from them, and the sexual organs are already outlined; doubtless, however, this stage is preceded by one that corresponds to the scolex of the genus in question, and which represents the actual larval stage. In such cases the development of the body of the tapeworm from the scolex has already begun within the first or intermediate host; in other cases, except in the single-jointed (monozootic) Cestodes, this only takes place in the definitive host. The direct metamorphosis of the oncosphere into the larval forms termed PLEROCERCOID has hitherto not been investigated, although Ligula, Schistocephalus and Bothriocephalus are very common parasites, but many circumstances point to the conclusions arrived at by us and by other observers. In the larval stages of other tapeworms we can always distinguish the scolex and a caudal-like appendage, vesicular in the cysticerci (fig.200), compact in the cysticercoids (fig.231). The scolex alone forms the future tapeworm, the variously formed appendage perishing.
It has now been proved that the appendage, the caudal vesicle, originates direct from the body of the oncosphere, and therefore is primary, and that the scolex only subsequently forms through proliferation on the surface of this appendage. On account of this origin the scolex is generally regarded as the daughter, and the part usually designated as the appendage as the mother, originating from the oncosphere.
Accordingly, two modes of development of the larval stage may be distinguished; in the one case, plerocerci and plerocercoids, the oncosphere changes directly into the scolex, thus forming the body of the tapeworm within the primary host; in the other case, cysticerci and cysticercoids, the scolex only forms secondarily in the transformed body of the oncosphere, which later on perishes, the scolex alone remaining as the originator of the tapeworm colony.
We may summarize briefly what has been said regarding these larval forms. We have, firstly, solid larval forms without any bladder. These arise directly from the oncosphere and are of two kinds, plerocercus and plerocercoid. Plerocercus is a solid globular larva with the head invaginated into the posterior portion. Plerocercoid (fig.208) is a solid elongated larva also with the head invaginated into the posterior portion, which is sometimes very long. Secondly, we have larval forms with bladders from which the scolices arise thus indirectly from the oncosphere. They are of two kinds, cysticercoid and cysticercus.
Cysticercoid.—The bladder is but slightly developed and is usually absorbed again. The anterior portion is, moreover, retracted into the posterior, and in some cases there is a long or a stumpy tail (figs.220, 231).
Cysticercus, or true bladder worms. (These may be divided into (1) cysticercus proper, consisting of a bladder and one scolex; (2) coenurus, a bladder and many scolices; (3) echinococcus, a bladder in which daughter bladders or cysts are developed, and then in these multiple scolices.)
Fig. 198.—Diagram of a cysticercoid. Cf. figs.220, 227. c.v., caudal vesicle or bladder (small); sec. c., secondary cavity caused by the growth forward of the hind-body; t., tail bearing six spines. (Stephens.)
Fig. 199.—Diagram of a cysticercus. c.v., caudal vesicle or bladder; i., invagination of wall of bladder. (Stephens.)
In the case of cysticerci a papilliform invagination forms, projecting into the interior of the bladder (fig.201). The layer of cells forming the papilla becomes divided into two laminÆ, the outer279 of which forms a kind of investing membrane (receptaculum capitis) for the papilla. The head and suckers are now developed on the walls bounding the axial lumen of the papilla. The papilla eventually
Our knowledge of the development of cysticerci in the wide sense of the word is limited almost exclusively to that of a few true “bladder worms” (cysticerci); in other cases we know either only the terminal stage, i.e., the complete larva, or, exceptionally, one of the intermediate stages, but we are not acquainted with a complete series; the description must therefore be incomplete.
We know from feeding experiments that, after the introduction of mature proglottids or of the fully developed ova of TÆnia crassicollis (of the cat) into the stomach of mice, the oncospheres escape from the shell in the middle portion of the small intestine, and a few hours later penetrate into the intestinal wall by means of a boring movement; they have been found in this position twenty-seven to thirty hours after the infection. By means of this migration, for which purpose they employ their spines, they attain the blood-vessels of the intestine; indeed, already nine hours after the infection and later they are found in the blood of the portal vein, and in the course of the second day after infection they are found in the capillaries of the liver, which these larvÆ do not leave.
Leuckart, in experimental feeding of rabbits with oncospheres of TÆnia serrata (of the dog), found free oncospheres in the stomach of the experimental animal, but not in the intestine: however, he came across them again in the blood of the portal vein. The passage through the blood-vessels to the liver is the normal one for those species of TÆnia the eggs of which become larvae in mammals; even in those cases in which the oncospheres develop further in the omentum or in the abdominal cavity (Cysticercus tenuicollis, C. pisiformis), there are distinct changes observable in the liver that lead one to the conclusion that there has been a secondary migration out of the liver into the abdominal cavity. Indeed, one must not imagine that the young stages of the Cestodes are absolutely passive; once they have invaded an organ they travel actively, and leave distinct traces of their passage.
In other cases the oncospheres leave the liver with the circulation, and are thus distributed further in the body; they may settle and develop in one or more organs or tissues. Many oncospheres may, by travelling through the intestinal wall, penetrate through it and attain the abdominal cavity direct; some, perhaps, pass also into the lymph stream. Where there are no blood and lymphatic vessels in the intestinal wall, as in insects, the oncospheres attain the body cavity or its organs direct; in short, they never remain in the intestinal lumen itself, and only rarely—as in Hymenolepis murina of the rat—do they remain in the intestinal wall.
When the infection has been intense, and the body is crowded with numerous oncospheres, acute feverish symptoms, are induced, to which the infected animals usually succumb (“acute cestode tuberculosis”); while in other cases the alterations in the organs attacked—as the liver in mice and the brain in sheep—may cause death.
Sooner or later the oncospheres of tapeworms come to rest, and are first transformed into a bladder, which may be round or oval according to the species. The embryonal spines disappear sooner or later, or remain close together or spread over some part of the bladder wall (fig.200). Their discovery by V. Stein in the bladder worm of the “meal worm” (the larva of a beetle, Tenebrio molitor) first led to the conclusion that bladder worms (cysticerci) actually originate from the oncospheres of TÆniidÆ.
Fig. 200.—Diagram of development of a cysticercus. 1, solid oncosphere with six spines; 2, bladder formed by liquefaction of contents; 3, invagination of bladder wall; 4, formation of rostellum (with hooklets) and suckers at the bottom of the invagination; 5, evagination of head; 6, complete evagination effected by pressure. (Stephens.)
The bladder may remain as a bladder, and then by proliferation the scolex forms on its wall (fig.202), or it may divide into an anterior so-called “cystic” portion and a solid tail-like appendage of various lengths, on which the embryonal hooks are to be found, and this is particularly the case in those larval forms (cysticercoids), e.g., those of Dipylidium caninum, that develop in invertebrate animals, such as Arthropoda.
As mentioned above one may regard the scolex as an individual that originates through proliferation of the wall of the parent cyst, mostly singly, but in those cysticerci that are termed coenurus (fig.201) many scolices occur, whereas in those called echinococcus the parent cyst originating from the oncosphere of TÆnia echinococcus (of the dog) first produces a number of daughter cysts, which in their
Fig. 201.—Section through a piece of a Coenurus cerebralis, with four cephalic invaginations in different stages of development. At the bottom of the invaginations the rostellum, hooks and suckers develop. (From a wax model.)
Fig. 202.—Median section through a cysticercus, with developed scolex at the bottom of the invagination. (After Leuckart.)
The rudiment of the scolex appears as a hollow bud, the cephalic invagination usually directed towards the interior of the bladder cavity; on its invaginated surface arise the four suckers, and the rostellum with the hook apparatus is formed in its blind end; we thus get a TÆnia head, but with the position of the parts reversed (fig.201). In many cysticerci the head rises up from the base of the cephalic invagination and is then surrounded by the latter. A more or less elongated piece of neck also develops, and even proglottids may appear, as in Cysticercus fasciolaris (the larva of TÆnia crassicollis of the cat) of the MuridÆ, a process somewhat analogous to that of Ligula, etc.
The period that elapses from the time of infection till the cysticercus is fully developed varies according to the species; the cysticercus of TÆnia saginata requires twenty-eight weeks, that of T. marginata seven to eight weeks, that of T. solium three to four months, and that of T. echinococcus longer still.
Fig. 203.—Cysticercus pisiformis in an evaginated condition, with neck, fore-body and bladder, with excretory network in its wall. 18/1.
With one single exception (Archigetes) the larvÆ do not become sexually mature in the organ where they have developed; they must enter the terminal host, a matter that is usually purely passive, the carriers of the larvÆ or infected parts of them being usually devoured by other animals. In this manner, for instance, the larvÆ (Cysticercus fasciolaris) found in mice and rats reach
The METAMORPHOSIS OF THE LARVA into the tapeworm is rarely accomplished in a simple manner; the transformation, however, is not complex in the single-jointed Cestodes, nor in Ligula and Schistocephalus; the latter is swallowed by birds (Mergus, Anas, etc.), produces eggs after only a few days, and very soon quits the intestine of its terminal host. In all other cases it is the scolex only which, by proliferating at its posterior extremity, forms the proglottids, after having invaded as a larva the intestine of a suitable host. The mother cysts, or what corresponds to them, die, are digested, absorbed, or perhaps even eliminated; on the contrary, segments found on the scolex during the larval stage, also in the case of Cysticercus fasciolaris, are retained. It is not certain whether the larvÆ of Dibothriocephalus lose any part.
The time required by the scolex to complete the entire chain of proglottids does not depend only on the number it has to produce, for TÆnia echinococcus, which, as a rule, only possesses three or four segments, takes quite as long a time for their growth (eleven to twelve weeks) as T. solium with its numerous segments; T. coenurus is fully developed in three to four weeks, and the same holds good for Dibothriocephalus latus, which possesses many more segments than the above-mentioned TÆnia of the dog. In a number of species it has been possible to determine fairly accurately the average daily growth; for instance, in Dibothriocephalus latus the daily growth is 8cm., in TÆnia saginata 7cm., etc.
The history of the development of the Cestodes demonstrates that persons and beasts harbouring larval tapeworms have become infected by having swallowed the oncospheres of the species of tapeworm to which they belong. In regard to Hymenolepis murina alone, it is known that the introduction of the oncospheres into those species of animals which harbour the adult tapeworm leads to the formation of the latter after the development of a larval stage in the intestinal wall; nevertheless, only young animals (rats) are capable of infection, for a previous infection, or the presence of mature tapeworms in the intestine, appears to produce a kind of immunity.
Biology.
In their adult stage, the tapeworms inhabit almost exclusively the alimentary canal of vertebrate animals, with but few exceptions the small intestine, and a few species select definite parts of it. A small number of RhynchobothriidÆ of marine fishes live apparently always in the stomach, while in rays and sharks the spiral intestine is their exclusive site. Bothriocephali generally attach themselves with their head on to the appendices of the pylorus of fishes; other species (Hymenolepis diminuta) occasionally fix their head in the ductus choledochus, and this is more frequent still in the tapeworms of the rock badger (Hyrax), which occasionally penetrate entirely into the biliary ducts. Stilesia hepatica, Wolffh., has so far only been found in the bile-ducts of its host (sheep and goat, East Africa).
In the disease of sheep induced by Cestodes, the worms have been observed also in the pancreas. Specimens found in the large intestines were probably being evacuated.
The Cestodes are looked upon as fairly inert creatures, this opinion having been formed by observing their condition in the cold cadavers of warm-blooded animals. Actually, however, they are exceedingly active, and accomplish local movements within the intestine, for they have been found in the ducts communicating with
They also invade other abdominal organs through abnormal communications, or through any that may be temporarily open between the intestine and such organs; they thus reach the abdominal cavity or the urinary bladder, or they work their way through the peritoneum.
They produce changes in the intestinal mucous membrane at the place of their attachment, the alterations varying in intensity according to the structure of the fixation organs. The mucous membrane is elevated in knob-like areas by the suckers; the epithelial cells become atrophied or may be entirely obliterated. Dipylidium caninum bores into the openings of LieberkÜhn’s glands with its rostellum, dilating the lumen to two or three times its normal size, while the suckers remain fixed between the basal parts of the cells. Species with powerful armatures penetrate deeper into the submucosa, and some that are not provided with exceptionally strong armatures, or are even unarmed, may be actually found with the scolex embedded in the muscles of the intestinal walls or even protruding beyond (TÆnia tetragona, Mol., in fowls, etc.). Other species, again, even cause perforation of the walls of the intestine of their hosts.
It is generally assumed that tapeworms, which almost without exception live in the gut of vertebrates, get their nutriment from the gut contents, which apparently they absorb through the whole body surface (cuticular trophopores). In favour of this view is the existence of fat drops in the proglottids, the identity in colour in certain forms between that of the fresh worm and the gut contents and the passage of certain substances derived from medicines (iron and mercury preparation) into the worms in the gut, etc. Whether the suckers are concerned in the absorption of nutriment and to what extent is still questionable.
The length of life of the adult tapeworm certainly varies; as a rule it appears to last only about a year; in other cases (Ligula) it averages only a few days, but we are likewise aware that certain species of Cestodes of man attain an age of several or many years (thirty-five). The natural death of Cestodes often appears to be brought about by alterations in the scolex, such as loss of the hooks, atrophy of the suckers and rostellum, finally the dropping off of the scolex; it is unknown whether a chain of segments deprived of its scolex then perishes or whether it first attains maturity. It has already been mentioned that in a few species the foremost proglottids are transformed into organs of fixation on the normal loss of the scolex.
Abnormalities and malformations are encountered relatively frequently in the Cestodes—such as abnormally short or long segments; the so-called triangular tapeworms, which—if belonging to the TÆniidÆ—always possess six suckers; often
Classification of the Cestoda of Man.
Order. Pseudophyllidea, Carus, 1863.
Scolex without proboscis or rostellum. Head “stalk” absent.
Scolex never with four, generally with two (or one terminal) bothria.280 Vitellaria numerous. Uterine opening present. Genitalia do not atrophy when uterus is developed. In large majority of proglottids eggs (or, if formed, their contents) are at the same stage of development.
Family. DibothriocephalidÆ, LÜhe, 1902.
Syn.: DiphyllobothriidÆ, LÜhe, 1910.
Genitalia repeated in each proglottid (polyzootic Cestodes). Ventral and dorsal surfaces flat. Cirrus unarmed. Cirrus and vagina if non-marginal open on the same surface as the uterus. Uterus long, convoluted, often forming a “rosette,” never dilates into a uterine cavity. Eggs thick shelled, operculated, constantly being formed in mature proglottids.
Sub-family. DibothriocephalinÆ, LÜhe, 1899.
Syn.: DiphyllobothriinÆ, LÜhe, 1910.
Segmentation distinct. Scolex unarmed, elongated, sharply separated (generally by a neck) from the first proglottis. Cirrus and vagina open ventrally. Genital pores non-alternating. Vas deferens surrounded by a muscular bulb. Receptaculum seminis large, sharply separated from the spermatic duct.
Order. Cyclophyllidea, v. Beneden.
Four suckers always present. Uterine opening absent. Vitellarium single. Genitalia atrophy when uterus is fully developed.
Family. DipylidiidÆ, LÜhe, 1910.
Rostellum if present armed. Suckers unarmed. Uterus breaks up into egg capsules. Paruterine organs absent.
Family. HymenolepididÆ, Railliet and Henry, 1909.
Segment always broader than long. Genitalia single. Longitudinal muscles in two layers. Genital pores unilateral. Testes one to four. Uterus persistent, sac-like. Eggs with three shells.
Family. DavaineidÆ, Fuhrmann, 1907.
Rostellum cushion-shaped. Armed with numerous (sixty to several thousand) hammer-shaped hooks in two (rarely one) rows.
Sub-family. DavaineinÆ, Braun, 1900.
Suckers armed. Uterus breaks up into egg capsules. Paruterine organs absent.
Family. TÆniidÆ, Ludwig, 1886.
Suckers unarmed. Uterus with median longitudinal stem and lateral branches. Female genitalia at the hind end of the proglottis. Genital pore irregularly alternating. Testes numerous in front of female genitalia. Ovary with two lobes (wings). Vitellarium behind the ovary. Embryophore radially striated.
The Cestodes of Man.
Most of the species to be mentioned live in man in their adult stage and occupy the small intestine; man is the definite host of these parasites, but is not the specific host for all the species; some of these species, as well as others (of mammals), may occur in man also in the larval stage.
Family. DibothriocephalidÆ.
Sub-family. DibothriocephalinÆ.
Genus. Dibothriocephalus, LÜhe, 1899.
Syn.: Diphyllobothrium, Cobbold, 1858; Bothriocephalus, p. p. Rud., 1819; Dibothrius, p. p. Rud., 1819; Dibothrium, p. p. Dies., 1850.
Scolex egg-shaped; dorsal and ventral bothria elongated, moderately strong, cutting rather deeply into the head; genitalia single in each proglottis; papillÆ in the vicinity of the genital atrium; the testes and vitellaria are in the lateral fields, the
Dibothriocephalus latus, L., 1748.
Syn.: TÆnia lata, L., 1748; TÆnia vulgaris, L., 1748; TÆnia grisea, Pallas, 1796; TÆnia membranacea, Pall., 1781; TÆnia tenella, Pall., 1781; TÆnia dentata, Batsch, 1786; Bothriocephalus latus, Bremser, 1819; Dibothrium latum, Dies., 1850; Bothriocephalus cristatus, Davaine, 1874281; Bothriocephalus balticus, Kchnmstr., 1855; Bothriocephalus latissimus, Bugn., 1886.
Length 2 to 9m. or more; colour yellowish-grey; after lying in water the lateral areas become brownish and the uterine rosette brown. The head is almond-shaped, 2 to 3mm. in length, the dorso-ventral axis is longer than the transverse diameter; the head, therefore, generally lying flat, conceals the suctorial grooves at the borders; these suckers are deep and have sharp edges (fig.205). The neck varies in length according to the degree of contraction and is very thin; there are 3,000 to 4,200 proglottids and there may be more; their breadth is usually greater than their length, but in the posterior third of the body they are almost square, and the very oldest are not uncommonly longer than they are broad. There are numerous testes situated dorsally in the medullary layer of the lateral fields; the vas deferens (fig.192) passes dorsally in transverse loops in the central field anteriorly and forms a seminal vesicle before its entry into the large cirrus pouch.
The orifice of the vagina is close behind the orifice of the cirrus; the former passes almost straight along the median line posteriorly, and widens into a receptaculum seminis shortly before its junction with the oviduct; the ovary is bilobed, in shape like the wings of a butterfly, ventrally in the medullary layer; the shell glands lie in the posterior recess of the ovary; the uterus, forming numerous transverse convolutions, passes ventral to the vas deferens forwards. Eggs (fig.207) large, with brownish shells and small lids, 68µ to 71µ by 45µ; the ovarian cell, which is already, as a rule, in process of segmentation, is surrounded by numerous large yolk cells; the proglottids nearest the posterior extremity are frequently eggless.
Fig. 204.—Various chains of segments of Dibothriocephalus latus, showing the central uterine rosette. (Natural size.)
Fig. 205.—Transverse section of the head of Dibothriocephalus latus. 30/1.
Fig. 206.—Fairly mature proglottis of Dibothriocephalus latus. The vitellaria are at the sides; the uterus, filled with eggs, is in the middle, also the vagina (the dark stripe passing almost straight from the front to the back), and the vas deferens (almost hidden by the uterus). Above in the centre is the cirrus sac, and below the shell gland and ovary are seen. 15/1. (From a stained preparation.)
The eggs, which are deposited in the intestine and evacuated
Fig. 207.—Dibothriocephalus latus: development of egg. 1, segmentation complete; some cells of the blastosphere have migrated through the yolk and have flattened to form c, the yolk envelope; others form a layer of flattened cells (e) forming the embryophore; the remaining cells (d) of the blastosphere form the hexacanth embryo. 2, embryophore (e) is becoming thicker. 3, the ciliated embryo has been pressed out of the shell; s', the operculum; c, the yolk envelope remaining in the shell (s); y, the yolk consisting of separate cells. 4, a free-swimming larva much swollen by the water. (After Benham and Schauinsland.)
Fig. 208.—Plerocercoid of Dibothricephalus latus. A., with the head evaginated; B., with the head invaginated. From the muscle of the pike.
The “broad tapeworm” is a frequent parasite of man in some districts, but it also occurs in the domestic dog, and on rare occasions is found in the domestic cat (together with Dibothriocephalus felis, Crepl.) and fox. French Switzerland and the Baltic Provinces of Russia are the centres of distribution; from the former districts the distribution radiates to France and Italy (Lombardy, Piedmont); from the Baltic Provinces over Ingermanland to Petrograd, over Finland to Sweden (on the shore of the Gulf of Bothnia), in a southerly direction to Poland, and into the Russian Empire and across it to Roumania, and towards the west along the coast of the Baltic Sea to the North Sea, where, however, its frequency considerably diminishes (Holland, Belgium, and the North of France).
In Turkestan and Japan the “broad tapeworm” is the most frequent parasite of man; it has been reported in Africa from the vicinity of Lake N’gami as well as from Madagascar; cases, in part at least imported, have also come under observation in North America.
In Germany Dibothriocephalus latus—apart from the fact that it is undoubtedly imported from Switzerland, Russia or Italy—is
It is also found in Munich and in the vicinity of the Lake of Starnberg (Bollinger).
Krabbe found it in 10 per cent. of the sufferers from tapeworms in Denmark; Szydlowski found the ova of this worm in Dorpat in 10 per cent. of the fÆces examined; Kruse found the worm in 6 per cent. of post-mortems; Kessler, in Petrograd, found the eggs in the fÆces in 7·8 per cent.; at post-mortems he found the worms in 1·17 per cent., though Winogradoff only found it in 0·8 per cent. In Moscow, according to Baranovsky, 8·9 per cent. of the fÆces examined contained the ova of Dibothriocephalus. In the interior and southern provinces of Sweden the worm, according to LÖnnberg, is only found sporadically, but, on the other hand, in Angermanland about 10 per cent. of the population is affected; while again in Norbotten the majority of persons are affected, and in Haparanda the entire population (with the exception of infants) harbour this parasite. In Switzerland D. latus is very frequent in close proximity to the lakes of Bieler, Neuchatel, Morat and Geneva (according to Zaeslin 10 to 15 to 20 per cent. of the population are affected); the parasite is less frequent in districts one to four hours removed from these lakes.
Of the fish from Swiss lakes examined by Schor those from Lake Geneva were most commonly infected, and especially Lota sp. and Perea sp.
The frequency and distribution have, nevertheless, decreased perceptibly in places; at the commencement of the eighteenth century the broad tapeworm was very common in Paris, at the present date it only occurs when imported (Blanchard); in Geneva, also, according to Zschokke, it has become rarer (formerly 10 per cent., now only 1 per cent.).
The disturbances produced in man by the presence of broad tapeworms are, as a rule, very trifling; in other cases they produce partly gastric disorders and partly nervous symptoms; in a number of cases, again, they set up severe anÆmia, apparently caused by toxins produced by the worms and absorbed by the host. There is no danger of auto-infection, as the larval stage lives only in fishes, not in warm-blooded animals. The case reported by Meschede (ova like those of Dibothriocephalus latus in the brain of a man who had suffered from epilepsy for six years) must be otherwise explained.
Fig. 209.—A piece of the body wall of the Burbot, Lota vulgaris. The tangential section has exposed the muscles of the trunk, with a plerocercoid of Dibothriocephalus latus. Natural size.
Human beings, like other hosts, can only acquire the broad
The life of D. latus is a very long one (six to fourteen years), as is deduced from persons who have left D. latus regions after they have been infected.
According to the experiments of M. Schor, plerocercoids of D. latus placed in slowly warmed water completely lose their movement at 54° to 55°C.; they survive the death of their host for several days; they are killed by low temperatures -3° to +1°C. in two days; strong acids and salt solutions kill them at once, also high temperatures, but all the same at least ten minutes is required in boiling or frying fish in order to kill the plerocercoids with certainty.
Dibothriocephalus cordatus, R. Lkt., 1863.
Syn.: Bothriocephalus cordatus, R. Lkt.
Fig. 210.—Cephalic end of Dibothriocephalus cordatus; on the left viewed sideways, on the right from the dorsal surface, showing a suctorial groove. (After Leuckart.)
Length, 80 to 115cm.; the head is heart-shaped and measures 2 by 2mm. The suctorial grooves are on the flat surface; the segments commence close behind the head and increase rapidly in breadth. At only 3cm. behind the head they are already mature; the greatest breadth attained by them averages 7 to 8mm., the length 3 to 4mm.; the number of proglottids averages 600; the most posterior ones are usually square. The uterine rosette is generally formed of six to eight lateral loops. The eggs are operculated and measure 75µ by 50µ.
Dibothriocephalus cordatus is a common parasite of the seal, the walrus and the dog in Greenland and Iceland, occasionally of man also. No doubt its larva lives in fishes.
The statement that D. cordatus also occurs in Dorpat in human beings has been proved erroneous (Zool. Anzeiger, 1882, v, p.46), as also has the report that this worm lives in hares in the neighbourhood of Berlin, whither it was supposed to have been carried by Esquimaux dogs (Rosenkranz in Deutsch. med. Wochenschr., 1877, iii, p.620). The parasite stated by the author to be D. cordatus is TÆnia pectinata, Goeze, which has been known since 1766.
Dibothriocephalus parvus, Stephens, 1908.
Largest gravid segments 5 by 3mm. Uterus forms a central rosette with four to five loops on each side of median line. In a proglottid measuring 3·5 by 2·25mm. the genital atrium is situated 0·4 to 0·5mm. behind the anterior margin and the uterine opening the same distance behind the genital atrium. Calcareous corpuscles absent in the preserved specimens. Eggs operculated, 59·2µ by 40·7µ.
Distinguished from Dibothriocephalus latus—(1) by the size of gravid segments (the minimum width of gravid segments of D. latus is 10 to 12mm., so that D. parvus is a much smaller worm); (2) quadrate segments of D. latus measure 6 by 6mm., those of D. parvus 4 by 4mm.; (3) by the eggs.
From D. cordatus it is distinguished by—(1) D. cordatus has only fifty immature segments, D. parvus has at least 200, possibly more; (2) mature segments of D. cordatus measure 7 to 8mm., maximum width of D. parvus is 5mm.; (3) quadrate segments of D. cordatus measure 5 to 6mm.; (4) D. cordatus has six to eight uterine loops; (5) D. cordatus measures 75µ to 80µ by 50µ.
Habitat.—Intestine of man (Syrian, in Tasmania).
Genus. Diplogonoporus, LÖnnbrg., 1892.
Syn.: Krabbea, R. Blanch., 1894.
The scolex is short and has powerful suctorial grooves; no neck; the proglottids are short and broad; there are two sets of genital organs side by side in each segment, which in all essentials resemble the single one of Dibothriocephalus.
Parasitic in whales and seals, occasionally in man.
Diplogonoporus grandis, R. Blanch., 1894.
Syn.: Bothriocephalus sp., Ijima et Kurimoto, 1894; Krabbea grandis, R. Blanch.
Scolex unknown; chain of proglottids over 10m. in length, 1·5mm. broad anteriorly, 25mm. broad posteriorly. The proglottids are very short (0·45mm.), but 14 to 16mm. broad. On either side to the right and left of the worm, along the entire ventral surface, there is a longitudinal groove; these grooves are nearer to each other than
Fig. 211.—Diplogonoporus grandis, LÜhe, 1899: ventral view of a portion of the strobila, showing two rows of genital pores and partially extruded cirri. (After Ijima and Kurimoto.)
Fig. 212.—Diplogonoporus grandis: ventral view (diagrammatic) of genitalia of left side; cir, cirrus; cir.o, cirrus opening; dtg., vitelline duct; ov., ovary; ovd., oviduct; sb., receptaculum seminis; ut., uterus; ut.o., uterine pore; vag., vagina; vag.o., vaginal pore; vd, vas deferens. ×150. (After Ijima and Kurimoto.)
Sparganum, Diesing, 1854.
The term Sparganum, invented by Diesing, is used as a group name of larval bothriocephalid Cestodes whose development is not sufficiently advanced to enable them to be assigned to any particular genus.
Sparganum mansoni, Cobb., 1883.
Syn.: Ligula mansoni, Cobbold, 1883; Bothriocephalus linguloides, R. Lkt., 1886; Bothriocephalus mansoni, R. Blanch., 1886.
Fig. 213.—Cephalic end of Sparganum mansoni, Cobb. (After Leuckart.)
Fig. 214.—Sparganum mansoni: on the right in transverse section. Natural size. (After Ijima and Murata.)
These plerocercoids were discovered in 1882 by P. Manson during the post-mortem on a Chinaman who had died in Amoy,
The plerocercoid, which hitherto alone is known to us, attains a length of 30cm. and a breadth of 3 to 6 to 12mm. The ribbon-shaped body is wrinkled, the lateral borders are often somewhat thickened, so that the transverse section has the form of a biscuit; the anterior end is usually wider and has the head provided with two weak suctorial grooves, either retracted or protracted.
The parasite makes migrations within the body, and thus may reach the urinary passages; then it is either evacuated with the urine or has to be removed from the urethra; not rarely it causes non-inflammatory tumours on various parts of the skin, which are at times painful and at times vary in size.
Nothing is known of its development and origin.
Sparganum proliferum, Ijima, 1905.
Syn.: Plerocercoides prolifer, Ijima, 1905; Sparganum prolifer, Verdun, Manson, 1907.
Fig. 215.—Sparganum prolifer: left with buds, right extended. ×4. (After Ijima.)
These plerocercoids produce an acne-like condition of the skin. The condition is really one of capsules in great abundance in the subcutaneous tissue and less so in the corium and in the intermuscular connective tissue. The encapsuled worms in the corium feel like embedded rice grains and raise the epidermis, giving rise to an acne-like condition. Many thousands occur scattered over the body; in Ijima’s Japanese case there were over 10,000 in the left thigh. The worms when they first appear in the skin cause itching. The capsules are ovoid, generally about 1 to 2mm. in diameter, but they may be smaller and also much larger. The larger ones occur in the subcutaneous tissue. The capsules consist of dense tough connective tissue.
Each capsule, as a rule, contains one worm, but as many as seven may occur. The skin of areas that have been long infected is swollen
Fig. 216.—Sparganum proliferum. ×10. (After Stiles.)
The Worm.—The chief peculiarity is its irregular shape and its reproduction in the larval stage by forming supernumerary heads, which are supposed to wander about the body.
The simplest forms are thread-like bodies, flat or round, 3mm. long and 0·3mm. in diameter, but they may be 12mm. long by 2·5mm. broad. The narrow end is the head, which in life invaginates and evaginates, but there is no indication of any suckers, except an inconstant terminal depression. In addition to these simple forms the most complicated and irregular forms occur, due to the formation of buds (heads) at various parts. The detachment and growth of a head account for the presence of more than one worm in a cyst. The irregularity in form is also
Calcareous bodies in the Japanese worms were 7·5µ to 12µ; in the Florida worms 8·8µ to 17·6µ.
Fig. 217.—Dipylidium caninum: on the left, the scolex, neck and the first proglottids; on the right, at the top, a packet of ova; below, hooks of the rostellum, side and front views; below, an ovum. Various magnifications. (After Diamare.)
Fig. 218.—Dipylidium caninum; egg showing a, egg-shell (vitelline membrane of Moniez); b, albuminous coat; c, internal shell formed of or secreted by an outer layer of blastomeres (Moniez); d, hexacanth embryo. (After Benham and Moniez.)
Mode of Infection.—Probably from eating uncooked fish.
Distribution.—Japan, Florida.
Family. DipylidiidÆ, LÜhe, 1910.
Genus. Dipylidium, R. Lkt., 1863.
Rostellum retractile, with several rings of alternating hooks; the latter with a disc-like base, having the shape of the thorns of a rose. Genital pores opposite; genitalia double. Testes very numerous in the central field; ovary with two lobes; the vitellaria, which are smaller, behind them; the uterus forms a reticulum, in the network of which the testicular vesicles lie; later on it breaks up into sacs enclosing one or several eggs. The eggs have a double shell.
Dipylidium caninum, L., 1758.
Syn.: TÆnia canina, L., 1758, p. p.; TÆnia moniliformis, Pallas, 1781; TÆnia cucumerina, Bloch, 1782; TÆnia elliptica, Batsch, 1786; Dipylidium cucumerinum, Lkt., 1863.
This worm measures 15 to 35cm. in length and 1·5 to 3mm. in breadth. The scolex is small, rhomboidal, and has a club-shaped rostellum on which there are, in three to four rings, forty-eight to sixty hooks resembling rose thorns, the size of those in the foremost being 11µ to 15µ and those in the hindmost ring 6µ. The neck is very short, the most anterior segments broad and short, the middle as long as they are broad; the
Fig. 219.—Dipylidium caninum: central portion of a proglottis. C.p., cirrus sac; V.s., vitellaria; Ex.v., excretory vessels; T., testicles lying in the meshes of the uterine reticulum which laterally forms pouches; O., ovary; U., reticulum of uterus; V., vagina and seminal receptacle (below ovary). Magnified. (After Neumann and Railliet.)
Fig. 220.—Dipylidium caninum: development of embryo. 1, solid hexacanth embryo; 2, primitive lacuna (a) in the embryo; 3, elongation of hinder part, rudiments of sucker and rostellum appearing; 4, “body” and “tail” distinct, (b) and (c) excretory system; 5, fore-body invaginates into hind-body, excretory bladder has a pore; 6, tail has dropped off; scolex growing up into secondary cavity formed by fore-body; the primitive cavity has been absorbed at stage 4. (After Benham, Grassi and Rovelli.)
Dipylidium caninum is a common intestinal parasite of dogs, in which it grows larger (TÆnia cucumerina, Bloch) than in cats (T. elliptica, Batsch); it has, however, also been found in jackals, as well as in human beings, though in the latter it is of comparatively rare occurrence (twenty-four cases), and almost always affects children, generally of tender age. One-third of all the cases in children were sucklings, about a quarter of all the cases recorded were adults, and these occurred throughout all Europe with the exception of Spain and Italy.
The proglottids, which leave the intestine spontaneously, are recognizable by the naked eye on account of their form and reddish colour, as well as their two genital pores. As a rule, the presence of this parasite sets up no marked symptom in the patient.
Fig. 221.—Larva (cysticercoid) of Dipylidium caninum, consisting of body and tail. The latter is solid and bears on it the embryonal spines. The bladder, which was only slightly developed, has disappeared, and the fore-part of the body bearing the rostellum is now seen invaginated into the hind portion. The hooklets are shown in front of the excretory system which has now developed. At a further stage the tail drops off; the head now evaginates, but is still enclosed in a double-walled sac formed by the prolongation upwards on each side of the topmost parts of the body shown in the figure. Cf. fig.220, 6. Enlarged. (After Grassi and Rovelli.)
The corresponding larval form (cysticercoid) lives in the louse of the dog (Trichodectes canis), a fact that was first established by Melnikow and Leuckart; according to Grassi and Rovelli, as well
Family. HymenolepididÆ, Railliet and Henry, 1909.
Genus. Hymenolepis,282 Weinland, 1858.
Accessory sac (opening into genital atrium) usually absent. Vas deferens with an external (outside cirrus sac) and an internal (inside cirrus sac) “seminal vesicle.” Three testes in each proglottis. The eggs are round or oval with two to four distinct envelopes. In mammals and birds.
Fig. 222.—Hymenolepis nana, v. Sieb. About 12/1. (After Leuckart.)
Hymenolepis nana, v. Sieb., 1852.
Syn.: TÆnia nana, v. Sieb., 1852, nec van Beneden, 1867; TÆnia Ægyptiaca, Bil., 1852; Diplacanthus-nanus, Weinld., 1858; TÆnia (Hymenolepis) nana, Lkt., 1863.
The worm is 10 to 45mm. in length and 0·5 to 0·7mm. in breadth; the head is globular, 0·25 to 0·30mm. in diameter. The rostellum has a single circlet consisting of twenty-four or twenty-eight to thirty hooks, which are only 14µ to 18µ in length. The neck is moderately long; the proglottids are very narrow, up to 200 in number, 0·4 to 0·9mm. in breadth, and 0·014 to 0·030mm. in length. The eggs are globular or oval, 30µ to 37µ to 48µ; the oncospheres measure 16µ to 19µ in diameter, with two coats, separated by an intervening semi-fluid substance (fig.224).
This species was discovered by Bilharz in Cairo in 1851; it was found by him in great numbers in the intestine of a boy who had
Fig. 223.—Hymenolepis nana: head. Enlarged. (After Mertens.)
Fig. 224.—Hymenolepis nana: an egg. Highly magnified. (After Grassi.)
Fig. 225.—Longitudinal section through the intestinal villus of a rat, with the larva (cysticercoid) of Hymenolepis murina. Magnified. (After Grassi and Rovelli.)
Fig. 226.—Hymenolepis nana (murina): cross section of proglottis from a rat. c.p., cirrus sac; rec. sem., receptaculum seminis; s.g., shell gland; ov., ovary; t., testis; cort. par., cortical parenchyma; m.l.n., main lateral nerve; ex. can., excretory canal; y.g., vitellarium. (After v. Linstow.)
Fig. 227.—Hymenolepis nana: longitudinal section of an embryo. bl.p., anterior opening of secondary cavity; caud., caudal appendage; pr. cav., primary cavity; sec. cav., secondary cavity. Enlarged. (After Grassi and Rovelli.)
Fig. 228.—Hymenolepis diminuta: scolex. Magnified. (After Zschokke.)
The development as well as the manner of infection is still unknown; Grassi is of opinion that Hymenolepis nana is indeed merely a variety of Hymenolepis murina, Duj., which lives in rats.
Hymenolepis diminuta, Rud., 1819.
Syn.: TÆnia diminuta, Rud., 1819; TÆnia leptocephala, Crepl., 1825; TÆnia flavopunctata, Weinld., 1858; TÆnia varesina, E. Parona, 1884; TÆnia minima, Grassi, 1886.
This species measures 20 to 60cm. in length, and up to 3·5mm. in breadth; there are from 600 to 1,000 segments. The head is very small (0·2 to 0·5mm.), it is club-shaped and has a rudimentary unarmed rostellum; the neck is short; the mature segments are 3·5mm. in breadth, 0·66mm. in length; the eggs are round or oval. The outer egg-shell is yellowish and thickened, with indistinct radial stripes; the inner embryonal shell (embryophore) double, thin; the outer layer is somewhat pointed at the poles; oncosphere 28µ by 36µ. Between the inner and outer shells is a middle granular layer.
Hymenolepis diminuta lives in the intestine of rats—Mus decumanus (the sewer rat), Mus rattus (the black rat), and Mus alexandrinus, rarely in mice; it is occasionally also found in human beings.
Weinland described it from specimens collected by Dr. E. Palmer in 1842, in Boston, from a child aged 19 months, as T. flavopunctata. A second case relating to a three year old child, from Philadelphia, was only reported in 1889 by Leidy; a third case was simultaneously reported of a two year old girl in Varese (T. varesina); and Grassi described another case relating to a twelve year old girl from Catania (Sicily). Sonsino and Previtera reported
Fig. 229.—Hymenolepis diminuta: two proglottids showing testes (3), ovary and vagina. Slightly enlarged. (After Grassi.)
Fig. 230.—Hymenolepis diminuta: egg from man. (After Bizzozero.)
According to Grassi and Rovelli the larval stage lives in a small moth (Asopia farinalis), as well as in its larva, in an orthopteron (Anisolabis annulipes), and in coleoptera (Acis spinosa and Scaurus striatus). Experimental infections have been successful on rats as well as on human beings. In America other species of insects may be the intermediary hosts.
Fig. 231.—Hymenolepis diminuta: cysticercoid from the rat flea (Ceratophyllus fasciatus). a, remains of primary vesicle; b, fibrous layer; c, radially striated layer resembling cuticle; d, layer of columnar cells; e, parenchymatous layer of irregularly disposed cells; f, parenchymatous layer. (Stephens, after Nicoll and Minchin.)
Nicoll and Minchin283 found in the body cavity of 4 per cent. of rat fleas (Ceratophyllus fasciatus) the cysticercoid of Hymenolepis diminuta. That it belonged to this species was shown by its unarmed rostellum and by feeding; 340 fleas were fed to white rats and fourteen
Nicoll and Minchin (loc. cit.) found a cysticercoid284 in the rat flea Ceratophyllus fasciatus which was probably that of Hymenolepis murina. Body 0·16mm., tail 0·19mm., scolex 0·096mm. in diameter. Rostellum has twenty-three spines in a single row. Length 0·017mm., handle 0·01mm., guard 0·007mm., prong 0·007mm. Sucker 0·042mm. Although this cycle, then, for H. murina also exists, it is not probable that rats (or man in the case of H. nana if this be considered distinct) infect themselves in this way, as they hardly ingest all the necessary fleas to account for the massive infection which frequently exists in rats (and man), so that Grassi’s cycle holds good as the predominant method. Xenopsylla cheopis has also been found by Johnston to harbour both cysticercoids in Australia.
Fig. 232.—Hymenolepis lanceolata. Natural size. (After Goeze.) To the right above, two hooks. 120/1. (After Krabbe.)
Hymenolepis lanceolata, Bloch, 1782.
Syn.: TÆnia lanceolata, Bloch, 1782; DrepanidotÆnia lanceolata, Railliet, 1892.
The parasite measures 30 to 130mm. in length and 5 to 18mm. in breadth; the head is globular and very small; the
Fig. 233.—Hymenolepis lanceolata: diagram of female genitalia. ov., ovary; ovd., oviduct; rec. sem., receptaculum seminis; s.g., shell gland; ut., uterus; y.g., vitellarium. (After WolffhÜgel.)
It inhabits the intestine of the following birds: Domesticated ducks and geese, the Muscovy duck (Cairina moschata), white-headed duck (Erismatura leucocephala), the pochard (Nyroca rufina), and the flamingo (Phoenicopterus antiquorum). It has been recorded from Great Britain, France, Denmark, Austria and Germany.
Zschokke reports the receipt of two specimens which a twelve year old boy in Breslau evacuated spontaneously at two different times.
The corresponding larva, according to MrÁzek, lives in fresh water Cyclops; according to Dadai it is likewise found in another copepod, Diaptomus spinosus, but the hooks of Dadai’s larva differed in size.
Family. DavaineidÆ, Fuhrmann, 1907.
Sub-family. DavaineinÆ, Braun, 1900.
Genus. Davainea, R. Blanch., 1891.
The large scolex is more or less globular, much wider than the rostellum, which is furnished with two rings of very small and numerous hooks. Neck absent, proglottids few, genitalia single. Parasitic chiefly in birds.285
Fig. 234.—Scolex of Davainea madagascariensis. The hooks have fallen off. 14/1. (After Blanchard.)
Davainea madagascariensis, Davaine, 1869.
Syn.: TÆnia madagascariensis, Dav.; TÆnia demerariensis, Daniels, 1895.
This worm measures 25 to 30cm. in length; the head has four large round suckers; the rostellum has ninety hooks (18µ in length); there are 500 to 700 segments, of which the last 100 are filled with eggs and form half of the entire worm. The segments, when mature, measure 2mm. in length by 1·4mm. in breadth; genital pores unilateral; about fifty testes; the uterus consists of a number of
Davainea madagascariensis has hitherto been found in man only (eight times). Davaine described this species from fragments sent to him from Mayotta (Comoro Islands), which were found in two Creole children. Chevreau observed four cases in Port Louis (Mauritius), likewise in children; Leuckart received the first perfect specimen—it was obtained from a three year old boy, the son of a Danish captain, in Bangkok; Daniels, at the post-mortem of an adult native of George Town, Guiana, found two specimens (TÆnia demerariensis); and finally Blanchard describes another perfect specimen which was in Davaine’s collection of helminthes in Paris, and which was obtained from a little girl 3 years old, of Nossi-BÉ (Madagascar). The intermediate host is unknown.
Davainea (?) asiatica, v. Linst., 1901.
Syn.: TÆnia asiatica, v. Linstow.
There exists only one headless specimen of this species, which is not quite adult, and which is preserved in the Zoological Museum of the Imperial Academy of Science in Petrograd. It came from a human being and was found by Anger in Aschabad (Asiatic Russia, near the northern frontier of Persia). The specimen measures 298mm. in length. The breadth anteriorly is only 0·16mm., the posterior part measures 1·78mm. across. The number of segments is about 750. The genital pores are unilateral; the testes are globular and lie in a dorsal and ventral layer in the medullary layer; the cirrus pouch is pyriform, 0·079mm. in length and 0·049mm. in breadth; the female glands lie in the fore-part of the segments, the ovary reaching to the excretory vessels; the vitellarium is small and round. The vagina has a large fusiform receptaculum seminis; the uterus breaks up into sixty to seventy large, irregularly polyhedric eggsacs.
Family. TÆniidÆ, Ludwig, 1886.
Genus. TÆnia, L., 1758.286
With the characters of the family. In the genus CladotÆnia recognized by some authors, the testes encroach on the mid field and the uterine stem reaches the anterior end of the segment.
TÆnia solium, L., p. p., 1767.
Syn.: TÆnia cucurbitina, Pall., 1781; TÆnia pellucida, Goeze, 1782; TÆnia vulgaris, Werner, 1782; TÆnia dentata, Gmel., 1790; Halysis solium, Zeder, 1800; TÆnia humana armata, Brera, 1802; TÆnia (CystotÆnia) solium, Lkt., 1862.
The average length of the entire tapeworm is about 2 to 3m., but may be even more; the head is globular, 0·6 to 0·8 to 1·0mm. in diameter. The rostellum is short with a double circlet of hooks, twenty-two to thirty-two in number, usually twenty-six to twenty-eight; large and small hooks alternate regularly; the length of the large hooks is 0·16 to 0·18mm., of the small ones 0·11 to 0·14mm. The rostellum is sometimes pigmented. The suckers are hemispherical, 0·4 to 0·5mm. in diameter. The neck is fairly thin and long (5 to 10mm.). The proglottids, the number of which averages from 800 to 900, increase in size very gradually; at about 1m. behind the head they are square and have the genitalia fully developed. Segments sufficiently mature for detachment measure 10 to 12mm. in length by 5 to 6mm. in breadth. The genital pores alternate fairly evenly at the lateral margin a little behind the middle of each segment. The fully developed uterus consists of a median trunk, with seven to ten lateral branches at either side, some of which are again ramified. The eggs are oval, the egg-shell very thin and delicate; the embryonal shell (embryophore) is thick, with radial stripes; it is of a pale yellowish colour, globular, and measures 31µ to 36µ in diameter; the oncospheres, with six hooks, are likewise globular, and measure 20µ in diameter (fig.238).
Malformations are not so common as in T. saginata; they consist in two or several proglottids being partly or entirely fused, formation of single club-shaped segments, fenestration of long or short series of segments and so-called double formation, in which the head has six suckers and the segments exhibit a Y-shaped transverse section. The oncospheres occasionally also possess more than six hooklets. Very slender specimens have led to the description of a particular species or variety (T. tenella).
Fig. 235.—Two fairly mature proglottids of TÆnia solium, showing ovaries (one bi-lobed), vitellaria, central uterine stem, cirrus and vas deferens (above), vagina (below), testes (scattered), longitudinal and transverse excretory vessels.
Fig. 236.—Head of TÆnia solium. 45/1.
In its fully developed condition T. solium is found exclusively in man; the head is usually attached in the anterior third of the small intestine and the chain, in numerous convolutions, extends backwards; a few mature detached proglottids usually lie at the most posterior part, and these are usually evacuated during defÆcation. In exceptional cases single proglottids or whole worms may reach contiguous organs if abnormal communications with them exist; thus they may reach the abdominal cavity and the urinary bladder, or they may be found in a so-called worm abscess of the peritoneum; occasionally, in vomiting, single segments or several together may be brought up. Exceptionally it induces severe anÆmia.
The larval stage (Cysticercus cellulosÆ) that gives rise to TÆnia solium lives normally in the intramuscular connective tissue and other organs of the domestic pig, but it is known to exist also in a few other mammals, such as the wild boar, the sheep,287 the stag, dog, cat, brown bear and monkey, as well as in man. The cysticercus
Fig. 237.—Large and small hooks of TÆnia solium. 280/1. (After Leuckart.)
Fig. 238.—TÆnia solium. 21, Egg with external membrane; 22, without (embryophore). (After Leuckart.)
Even with the naked eye a white spot may be observed in the centre of the long equator, this being the invaginated head; it is easy to make it project by pressing on the vesicle (after tearing off with the finger-nail the investing connective tissue), and on examining it under the microscope one can convince oneself that it corresponds with the head of TÆnia solium.
Fig. 239.—Two mature proglottids of TÆnia solium with fully developed uterus. 2/1.
Numerous experiments have proved that the Cysticercus cellulosÆ of the pig, if introduced into the intestine of man, grows to a TÆnia solium (KÜchenmeister, 1855; Humbert, 1856; Leuckart, 1856; Hollenbach, 1859; Heller, 1876); the cysticercus has frequently also been cultivated purposely by feeding pigs with mature proglottids of T. solium (P.J. van Beneden, 1853; Haubner and KÜchenmeister, 1855; Leuckart, 1856; Mosler, 1865; Gerlach, 1870; etc.), but success did not attend the efforts to make Cysticercus cellulosÆ establish themselves in the intestines of pigs, dogs, guinea-pigs, rabbits and monkeys (Macacus cynomolgus), and so become adult TÆniÆ; the attempts, also, to infect dogs with cysticerci by means of ova were likewise, as a rule, abortive.288
The development of Cysticercus cellulosÆ takes two and a half to three or four months; it is not known how long the cysticerci remain alive in animals; not uncommonly they perish at earlier or later stages, and become calcified or caseated. Extracted cysticerci die in water at a temperature of 47° to 48°C., in flesh at normal temperature they remain alive for twenty-nine days or more. On account of the present rapid means of pickling and smoking meat, the cysticerci as a rule are not killed, also the effect of cold on them for some time in cold chambers of slaughterhouses is not lethal, but freezing is fatal (Ostertag).
There is not the least doubt that human beings are almost exclusively infected with TÆnia solium by eating pork containing cysticerci in a condition that does not endanger the life of the cysticerci. The infection may likewise be caused in man by eating the infected meat of other animals subject to this species of bladder worm, mainly, as a matter of fact, deer and wild boar.
The frequency of cysticerci in pigs’ flesh has considerably decreased since the introduction of meat inspection; in the Kingdom of Prussia there was on an average 1 infected pig to every 305 slaughtered between 1876 to 1882; from 1886 to 1889, there was 1 to 551; from 1890 to 1892, there was 1 to 817; in 1896, 1 to 1,470; and in 1899, 1 to 2,102; in the Kingdom of Saxony in 1894 there was 1 infected pig to every 636; in 1895 there was 1 to every 2,049, and in 1896 only 1 infected pig was found of 5,886 slaughtered. In South Germany pigs with cysticerci are very rare, but are more frequent in the eastern provinces of Prussia; in 1892 the number of infected pigs compared with the total slaughtered was as follows:—
| In the district of Marienwerder | 1 : 28 |
| " " Oppeln | 1 : 80 |
| " " KÖnigsberg | 1 : 108 |
| " " Stralsund and Posen | 1 : 187 |
| " " Danzig, Frankfort a. O. and Bromberg | 1 : 250 |
| As compared with the district of Arnsberg | 1 : 865 |
| " " " Coblenz | 1 : 975 |
| " " " DÜsseldorf | 1 : 1,070 |
| " " " MÜnster and Wiesbaden | 1 : 1,900 |
The average for the whole of Prussia in the same year was 1:1,290; for the eastern provinces, on the other hand, 1:604. Even more unfavourable are the proportions in Russian Poland (over 1 per cent. of pigs measly), in Prague (over 3 per cent.), in Bosnia and Herzegovina (6 to 7 per cent.). The cause for this is most likely attributable to the manner in which the pigs are kept. When allowed to be in the farmyards of the small farmers for the whole day, or allowed to wander in the village streets and pasture lands, they are more liable to take up the oncospheres of the T. solium than when shut up in good pig-styes.
The geographical distribution of T. solium generally corresponds with that of the domestic pig and the custom of eating pork in any form insufficiently cooked or raw. There are, or were, some isolated districts in Germany, France, Italy and England where the “armed tapeworm” was frequent (for instance, Thuringia, Brunswick, Saxony, Hesse, Westphalia, whereas it is and was very scarce in South Germany); it is thus easily understood why it occurs very rarely in the East, in Asia and in Africa, in consequence of the Mahommedans,
The occurrence of Cysticercus cellulosÆ in man has been known since 1558 (Rumler, Obs. med., liii, p.32); there is hardly an organ in man in which cysticerci have not been observed at some time; they are most frequently found in the brain,289 where they grow to a variety known as Cysticercus racemosus; next in frequency they are found in the eye, in the muscular system, in the heart, in the subcutaneous connective tissue, the liver, lungs, abdominal cavity, etc. The number of cysticerci observed in one man varies between a few and several thousands. Of the sexes, men are most subject (60 to 66 per cent. of the number attacked). The disturbances caused in man by cysticerci vary according to the nature or position of the organs attacked; when situated in the cerebral meninges they have the same effect as tumours.
During the last decades, however, these cases have also become less common. In Rudolphi’s time 2 per cent. of post-mortems in Berlin showed cysticerci; in the ’sixties, according to Virchow, about the same; in 1875 the number fell to 1·6 per cent.; in 1881 to 0·5 per cent.; in 1882 to 0·2 per cent.; in 1900 to 0·15 per cent., and in 1903 to 0·16 per cent. Hirschberg between 1869 and 1885 discovered cysticerci in the eye seventy times in 60,000 ophthalmic cases, but during the following six years the parasite was only present twice amongst a total of 46,000 cases of ophthalmic diseases, and since 1895 no ophthalmic case has been met with.
The infection of human beings with the cysticerci can only take place by the introduction of the oncospheres of TÆnia solium into the stomach with vegetable foods, salads that have been washed in impure water containing oncospheres, also by drinking contaminated water; the carriers of T. solium, moreover, infect themselves still more frequently through uncleanliness in defÆcation, the privies
On account of these dangers of internal or external auto-infection, it is therefore the duty of the medical attendant, after recognizing the presence of tapeworms, to expel them,290 and in doing so to employ every possible means to prevent vomiting setting in; it is, however, equally important to take the necessary steps to destroy the parasites evacuated. It may be incidentally mentioned that in using certain remedies the scolex not rarely remains in the intestine; the cure in such cases has not been accomplished, as the scolex again produces new proglottids, and after about eleven weeks the first formed ones are again mature and appear in the fÆces.
Amongst the cysticerci also many malformations appear; thus absence of the rostellum and the hooks, or double formation with six suckers, or abnormalities of growth on account of the surroundings, which have had a special name given to them, viz., Cysticercus racemosus, Zenk. (= C. botryoides, Hell.; C. multilocularis, Kchnmstr.); these forms are more especially found at the base of the brain, are irregularly ramified and often without the head.
A certain interest is attached to those forms that have led to the establishment of a distinct species:—
Cysticercus acanthotrias, Weinld., 1858.
In making the autopsy of a white Virginian woman who had died of phthisis, a cysticercus was found in the dura mater, and eleven or twelve specimens in the muscles and subcutaneous tissue. Weinland and Leuckart, who examined the specimens, found that they resembled Cysticercus cellulosÆ in form and size, but that they carried on the rostellum a triple crown, each consisting of fourteen to sixteen hooks, which differed from the hooks of C. cellulosÆ or of TÆnia solium by the greater length of the posterior root process and the more slender form of the hooks; the large hooks measured 0·153 to 0·196mm., the medium-sized hooks, 0·114 to 0·14mm., and the small ones 0·063 to 0·07mm.
On account of these differences a distinct species of cysticercus was established, and this naturally presupposed a corresponding species of TÆnia (T. acanthotrias, Lkt.); this could be done with
The duration of life of C. cellulosÆ in man is very long; cysticerci of the eye have been known to persist for twenty years, and in cysticercus of the brain ten to nineteen years may elapse from the first appearance of cerebral symptoms until death. Dead cysticerci may shrivel up or become calcified, perhaps also undergo fatty degeneration and then absorption. Finally, it may be mentioned that if particular proof is required that C. cellulosÆ of man belongs to the cycle of development of the TÆnia solium, such proof has been furnished by Redon.
Note.—TÆnia tenella, mentioned on p.332, was ascribed by Cobbold to cysticerci of the muscular system of sheep. It has, however, been demonstrated that these cysticerci belong to the cycle of development of TÆnia marginata (dog) (Cysticercus tenuicollis, from the omentum of sheep); but as already stated C. cellulosÆ also occurs in sheep. Chatin himself swallowed the cysticercus, which Cobbold termed C. ovis, without causing a TÆnia to develop in his intestine. MÜller also vainly sought to induce infection with C. tenuicollis in his own person. On the other hand, the feeding of a dog with Cysticercus ovis resulted in the production of TÆnia marginata.
TÆnia bremneri, Stephens, 1908.
Characterized by the large size of the gravid segments. The largest was 32 by 9mm. Smallest 21 by 6mm. Average 28·6 by 8·5mm. Mode 21 by 6mm. Uterine branches twenty-two to
TÆnia marginata, Batsch, 1786.
Syn.: T. e. Cysticerco tenuicolli, KÜchenmeister, 1853.
Fig. 240.—Large and small hooklets of TÆnia marginata. 280/1. (After Leuckart.)
This species, which in structure resembles TÆnia solium, lives in the intestine of the dog and the wolf. It attains 1·5 to 4m. in length, possesses a double crown of thirty to forty hooks, on an average thirty-six to thirty-eight hooks, and in its larval stage (Cysticercus tenuicollis) lives in the peritoneal cavity of ruminants and the pig, occasionally in the monkey and squirrel.
It is included in this work because, according to one statement, C. tenuicollis is supposed to have been observed in man in North America; but the case is not quite certain, as the number of hooks was less than in C. tenuicollis and coincided with C. cellulosÆ, although the size of the cysticercus appeared to point to C. tenuicollis. A yet earlier statement of Eschricht, that Cysticercus tenuicollis had been observed in Iceland in the liver of a man, is undoubtedly due to an error.
TÆnia serrata, Goeze, 1782.
This parasite attains a length of from 0·5 to 2m., possesses a double crown of thirty-four to forty-eight (mostly forty) hooks. It lives exclusively in the intestine of the dog, the corresponding cysticercus (Cysticercus pisiformis) living in the mesentery of the hare and rabbit. We mention this species with all reserve amongst the parasites of man, because Vital states that he has observed it twice in Constantine (Algeria) in human beings. The data, however, are not sufficient to characterize the species. It is highly probable that they relate to TÆnia solium. Galli-Valerio even swallowed five specimens of Cysticercus pisiformis, but without result.
TÆnia crassicollis, Rud., 1810.
I only mention this species from the intestine of the domestic cat because Krabbe regards its occurrence in man as possible. It attains a length of 60cm. and is armed; its cysticercus (Cysticercus fasciolaris) lives in the liver of mice and rats. In Jutland, according to Krabbe, chopped-up mice (spread on bread) are eaten raw, being a national remedy for retention of urine, and this custom affords the possibility of the introduction of C. fasciolaris into the intestine of man (Nord. med. Arkiv, 1880, xii).
TÆnia saginata, Goeze, 1782.
Fig. 241.—Mature segment of TÆnia saginata, G., with distended uterus. 2/1.
Syn.: TÆnia solium, L., 1767 (pro parte); TÆnia cucurbitina, Pallas, 1781 (p.p.); TÆnia inermis, Brera, 1802. Moquin-Tandon, 1860; TÆnia dentata, Nicolai, 1830; TÆnia lata, Pruner, 1847; Bothriocephalis tropicus, Schmidtmuller, 1847; TÆnia mediocanellata, KÜchenmeister, 1855; TÆnia zittavensis, KÜchenmeister, 1855; TÆnia tropica, Moquin-Tandon, 1860; TÆnia (CystotÆnia) mediocanellata, Leuckart, 1863.
Fig. 242.—Cephalic end of TÆnia saginata in the contracted condition. 8/1.
The length of the entire tapeworm averages 4 to 8 to 10m. and more, even up to 36m. According to BÉrenger-Feraud it attains a length of 74m. (?) The head is cubical in shape, 1·5 to 2mm. in diameter; the suckers are hemispherical (0·8mm.) and are frequently pigmented; there is a sucker-like organ in place of the rostellum, and this also is frequently pigmented. The neck is moderately long and about half the breadth of the head; the proglottids, the number of which averages more than 1,000, gradually increase in size; the mature detached segments are shaped exactly like pumpkin-seeds, and are about 16 to 20mm. in length and 4 to 7mm. in breadth. The genital pores alternate irregularly and are situated somewhat behind the middle of the lateral margin. There are twenty to thirty-five lateral branches at each side of the median trunk of the uterus, and these again ramify. The eggs are more or less globular, the egg-shell frequently remains intact and carries one or two filaments; the embryonal shell (embryophore) is thick, radially striated, is transparent and oval; it is 30µ to 40µ in length, and 20µ to 30µ in breadth. Several segments simultaneously are usually passed spontaneously with defÆcation.
Malformations are not uncommon, and resemble those of TÆnia solium; a triangular form has been termed T. capensis by KÜchenmeister, and T. lophosoma by Cobbold, names that naturally possess as little value as does the term T. fenestrata for fenestrated specimens. Moreover, T. solium, var. abietina, Weinld., 1858, which was evacuated by an Indian, was probably a T. saginata with somewhat close uterine branches. It is regarded by Stiles and Goldberger as a doubtful subspecies.
Fig. 243.—TÆnia saginata. 19, egg with external shell. 20, without (embryophore). (After Leuckart.)
T. saginata in its adult condition lives exclusively in the intestinal
Fig. 244.—A piece of the muscle of the ox, with three specimens of Cysticercus bovis. Natural size. (After Ostertag.)
Medical men observed that weakly children who were ordered to eat raw scraped beef to strengthen them contracted T. saginata. It was found, moreover, that Jews, who are prohibited from eating pork from religious motives, suffered especially from T. saginata; when T. solium was found to occur in a Jew he often confessed to having eaten pork; and finally it was found that certain nations—for instance, the Abyssinians—frequently harbour T. saginata, and only eat beef—raw by preference.
These observations led Leuckart, in 1861, to feed young calves with the proglottids of T. saginata in order to discover the corresponding cysticercus, which was then not known. This experiment was successful. Similar experiments, with similar results, were then conducted by Mosler (1863), Cobbold and Simonds (1864 and 1872), RÖll (1865), Gerlach (1870), ZÜrn (1872), Saint Cyr, Jolicoeur (1873), Masse and Pourquier (1876), and Perroncito, in 1876. The attempts to infect goats, sheep, dogs, pigs, rabbits and monkeys were unsuccessful. Only Zenker and Heller were able to infect kids, and Heller infected one sheep, but these are exceptions.
Artificial infections of human beings with Cysticercus bovis to obtain the tapeworm were less numerous, and indeed quite superfluous, yet this was also done by Oliver (1869) in India, and Perroncito (1877) in Italy. The experiments of the latter prove that the extracted cysticerci of the ox certainly perish in water at 47° to 48°C.
It is a remarkable circumstance that, at least as regards Central Europe, C. bovis in the ox, after natural infection, was so seldom found that almost every case was published as a rarity; whereas the TÆnia is very frequent in man. The reason for this is that in Germany cattle are not severely infected, and that the small, easily dried-up cysticerci easily escape notice in the large body of the host. Hertwig, the late director of the town cattle market in Berlin, in 1888, pointed out
| Year | Number of oxen slaughtered | Infected | Proportion |
| 1888–89 | 141,814 | 113 | 1 : 1,255 |
| 1889–90 | 154,218 | 390 | 1 : 395 |
| 1890–91 | 124,593 | 263 | 1 : 474 |
| 1891–92 | 136,368 | 252 | 1 : 541 |
| 1892–93 | 142,874 | 214 | 1 : 672 |
Since 1892 an increase has taken place in the number of oxen infected with cysticercus, but this is probably attributable to the more general and searching examinations. In the slaughter-houses of Prussia the number of infected beasts was as follows:—
| 1892 | 567 |
| 1893 | 686 |
| 1894 | 748 |
| 1895 | 1,143 |
| 1896 | 1,981 |
| 1897 | 2,629 |
The condition was most frequent in Neisse (3·2 to 4 per cent.), Eisenach (1·91 per cent.), Ohlau (1·57 per cent.), Oels i. Schles. (1 per cent.), Marienwerder (0·34 to 1·2 per cent.). The flesh of oxen only slightly infected (containing not more than ten living cysticerci) is sold in pieces of not more than 5lb. to consumers after having been rendered innocuous by cooking, or by pickling for twenty-one days in 25 per cent. salt brine, or hanging for twenty-one days in suitable refrigerators; oxen in which only one cysticercus is found are allowed free commerce, and those strongly infected (i.e., containing more than ten living cysticerci) may only be used for industrial purposes.
It is a striking fact that more bulls than cows are infected (according to Reissmann, in Berlin, from 1895 to 1902, 0·446 per cent. bulls, 0·439 per cent. oxen, and 0·262 per cent. cows), the explanation of which, according to Ostertag, is that most oxen are killed when young, when also infection most readily takes place, and, further, that the larva later on in life can be completely atrophied.
The cysticercus of the ox has hitherto been found in man on very rare occasions. Arndt (Zeitschr. f. Psychiat., xxiv) mentions a case in the brain, Heller in the eye, and Nabiers and Dubreith also in the brain (Journ. mÉd. Bordeaux, 1889–1890, p.209); but the diagnoses are not quite certain, as absence of hooks occasionally occurs in Cysticercus cellulosÆ.
TÆnia saginata is the most frequent tapeworm of man (with the exception of Dibothriocephalus latus in a few districts), and the parasite is widely distributed over the surface of the globe; it has been known in the East for ages, so far as data are available; it is frequent in Africa, America, and Europe. Its frequency has perceptibly increased during the last few years, but a decrease should soon take place in
The following table shows the relative frequency of the Cestodes of man:—
| Author | Year | Number of cases | T. saginata | T. solium | Dibr. latus | Dipyl. canin. | Unde- termined | ||
| Parona (Milan) | 1899 | 150 | 121 | 11 | 4 | — | 14 | ||
| Parona (Italy) | 1868–99 | 513 | 397 | 71 | 26 | — | 19 | ||
| Krabbe (Denmark) | 1869 | 100 | 37 | 53 | 9 | 1 | — | ||
| " " | 1869–86 | 200 | 153 | 24 | 16 | 8 | — | ||
| " " | 1887–95 | 100 | 89 | — | 5 | 6 | — | ||
| " " | 1896–1904 | 50 | 41 | 1 | 5 | 3 | — | ||
| Blanchard (Paris) | 1895 | ? | 1,000 | 21 | — | — | — | ||
| Stiles (United States) | 1895 | more than 300 | more than 300 | — | 3 | — | — | ||
| Schoch (Switzerland) | 1869 | 19 | 16 | 1 | 2 | — | — | ||
| Zaeslein (Switzerland) | 1881 | ? | 180 | 19 | ? | — | — | ||
| Kessler (Petrograd) | 1888 | ? | 22 | 16 | 47 | — | — | ||
| Mosler (Greifswald) | 1894 | 181 | 112 | 64 | 5 | — | — | ||
| Bollinger (Munich) | 1885 | 25 | 16 | 1 | 8 | — | — | ||
| Vierordt (TÜbingen) | 1885 | 121 | 113 | 8 | — | — | — | ||
| Mangold (TÜbingen) | 1885–94 | 128 | 120 | 6 | 8 | — | — | ||
TÆnia africana, v. Linst., 1900.
Fig. 245.—Mature segment of TÆnia africana. The ovary is in the middle, and behind it are the shell gland and vitellarium; at the sides are the testicles, and externally the excretory canals; the cirrus pouch, the vas deferens and the vagina are on the left. Magnified. (After v. Linstow.)
This worm measures over 1·3m. in length. The segments are all broader than they are long. The scolex is unarmed and is provided with an apical sucker (0·16mm.). The parasite measures 1·38mm. in breadth, 1·03mm. in width; the suckers measure 0·63mm. in diameter. The neck is very short and somewhat broader than the scolex; number of segments about 600; the hindmost segments measure 7mm. in length and 12 to 15mm. in breadth. The genital pores alternate irregularly in the middle of the lateral margin; the testes are very numerous and occupy the entire medullary layer; the vas deferens is much convoluted; the cirrus pouch
Fig. 246.—Proglottis of TÆnia africana, with uterus. Magnified. (After v. Linstow.)
Fig. 247.—Head of TÆnia africana; apical surface. Magnified. (After v. Linstow.)
At present only two specimens are known; they came from a black soldier from the vicinity of Lake Nyasa. The cysticercus is unknown; perhaps it lives in the zebu, the flesh of which the Askaris are in the habit of devouring uncooked.
TÆnia confusa, Ward, 1896.
Length 8·5m., breadth about 5mm. The scolex is unknown; there is no neck; number of proglottids 700 to 800, always longer than they are broad; the hindmost measure 35mm. in length, 4 to 5mm. in breadth; the genital pores alternate irregularly behind the middle of the lateral margin; testicles numerous; vas deferens not much coiled; the cirrus pouch thick walled, elongated and club-shaped, with globular vesicula seminalis; the cirrus is beset with little hairs; the receptaculum seminis is globular; ovary small, double; each half is bean-shaped; vitellarium narrow, triangular; shell gland globular; uterus with median trunk and fourteen to eighteen short ramified lateral branches on either side. The embryophores are oval (39µ by 30µ), thick and radially striated.
Fig. 248.—TÆnia confusa: mature segment showing central uterine stem, bilobed ovary, globular shell gland, triangular vitellarium, scattered testes, cirrus, vas deferens, and vagina. 15/1. (After Guyer.)
Fig. 249.—TÆnia confusa: gravid segment. 25/1. (After Ward.)
Of this species only two specimens have been recorded; they occurred in human beings and were sent at different times to the first describer of them by a doctor in Lincoln (Nebr.). Perhaps TÆnia solium, var. abietina, Weinld., which was found in a Chipeway Indian, is of the same species in spite of the shorter segments.
TÆnia echinococcus, v. Sieb., 1853.
Syn.: TÆnia nana, v. Ben., 1861 (nec v. Sieb., 1853); Echinococcifer echinococcus, Weinld., 1861.
Fig. 250.—TÆnia echinococcus: the cirrus sac, the vagina, uterus, ovary, shell gland and vitellarium, and the testicles at the sides are recognizable in the second proglottis; the posterior proglottis shows the uterus partly filled with eggs, as well as the cirrus sac and the vagina. 50/1.
TÆnia echinococcus measures 2·5 to 5 or 6mm. in length; the head is 0·3mm. in breadth, and has a double row of twenty-eight to fifty hooklets (on an average thirty-six to thirty-eight) on the rostellum.
The size and form of these hooklets vary (the larger ones are 0·040 to 0·045mm. in length, the smaller ones are 0·030 to 0·038mm. in length). The suckers measure 0·13mm. in diameter; the neck is short; there are only three or four segments, the posterior segment being about 2mm. in length and 0·5mm. in breadth. The genital pores alternate; there are forty to fifty testicles; the vas deferens
When mature this parasite lives in the small intestine of the domestic dog, the jackal, and the wolf, and apparently also in Felis concolor, and is usually present in great numbers; it can also be transmitted experimentally to the domestic cat, one successful result out of seven (DÉvÉ).292 The larval stage (Echinococcus polymorphus) lives in various organs—chiefly in the liver and lungs—of numerous species of mammals (twenty-seven), especially in sheep, ox and pig, and it is even not uncommon in man, though the TÆnia itself has never been found in a human being; accordingly man can only acquire the echinococcus by ingesting the eggs of the “dog worm.” The dogs disseminate the eggs of TÆnia echinococcus wherever they go, or carry them to their mouths and coats by biting up the evacuated segments, and are thus able to transmit them directly to human beings (by licking them or making use of the same crockery, etc.). In other cases the oncospheres, enclosed in the embryophores, must withstand desiccation for a time and then (as when the dogs are “kissed” or otherwise caressed) are transmitted into or on to
Echinococcus is very common in slaughtered animals; in Germany, however, the figures in the reports of the abattoirs present an erroneous view in so far as, besides the total number of animals slaughtered, only the numbers of those organs (liver and lungs) are published that were so severely infected with echinococci that, even when the parasites were “shelled” out, the flesh could not be placed upon the market and was therefore “condemned.”
In Berlin the following animals were slaughtered:—
| Year | 1889–90 | 1890–91 | 1891–92 | 1892–93 | 1896–97 | 1902 |
| Oxen | 154,218 | 124,593 | 136,368 | 142,874 | 146,612 | 153,748 |
| Sheep | 430,362 | 371,943 | 367,933 | 355,949 | 395,769 | 434,155 |
| Pigs | 442,115 | 472,859 | 530,551 | 518,073 | 694,170 | 778,538 |
During the same years the following were condemned in consequence of being infected with echinococci:—
| Lung | Liver | Lung | Liver | Lung | Liver | Lung | Liver | Lung | Liver | Lung | Liver | |
| Oxen | 7,266 | 2,418 | 5,792 | 1,938 | 4,497 | 1,721 | 2,563 | 739 | 3,284 | 1,156 | 2,507 | 791 |
| Sheep | 5,479 | 2,742 | 4,595 | 2,059 | 4,435 | 1,669 | 3,331 | 1,161 | 4,561 | 1,939 | 11,138 | 4,437 |
| Pigs | 6,523 | 5,078 | 5,083 | 3,735 | 6,037 | 4,374 | 6,785 | 4,312 | 7,888 | 5,398 | 9,544 | 9,233 |
Nevertheless there are statistics that give the total number of animals infected with echinococcus:—
| Author | Place | Oxen | Sheep | Pigs | |||
| LÄngrich | Rostock i. M. | 26 | ·2 per cent. | 37 | ·0 per cent. | 5 | ·4 per cent. |
| Olt | Stettin | 7 | ·1 " | 25 | ·8 " | 7 | ·3 " |
| Steuding | Gotha | 24 | ·6 " | 35 | ·4 " | 21 | ·4 " |
| Prettner | Prague | 23 | ·2 " | 5 | ·5 " | ? | |
In GÜstrow, in Mecklenburg, half of the animals slaughtered are said to be infected with echinococcus; in Wismar 25 per cent. of the oxen, 15 per cent. of the sheep and 5 per cent. of the pigs are infected; according to Mayer, in Leipzig, 3·79 per cent. native pigs, 24·47 per cent. Hungarian pigs, and 13·09 per cent. of sheep were infected with echinococcus; at the same time it was stated that in regard to the native pigs the liver was more frequently affected than the lungs (3·81 per cent. as compared with 0·26 per cent.); in sheep the lungs were more frequently infected
The data of Lichtenheld, in Leipzig, give the frequency with which various organs were affected, as shown in the following table:—
| Cattle | Pigs | Sheep | Horses | |||||||
| ? | ? | |||||||||
| Lungs | 69 | ·3 per cent. | 16 | ·2 per cent. | 21 | ·4 per cent. | 52 | ·2 per cent. | 5 | ·5 per cent. |
| Liver | 27 | ·0 " | 74 | ·2 " | 72 | ·0 " | 44 | ·9 " | 94 | ·5 " |
| Spleen | 2 | ·2 " | 3 | ·2 " | 2 | ·7 " | 2 | ·9 " | — | |
| Heart | 0 | ·75 " | 3 | ·2 " | 1 | ·3 " | — | — | ||
| Kidneys | 0 | ·75 " | 3 | ·2 " | 1 | ·3 " | — | — | ||
| Subperitoneal tissue | — | — | 1 | ·3 " | — | — | ||||
Structure and Development of Echinococcus (Hydatid).
Fig. 251.—Echinococcus veterinorum: the fibrous sac enclosing the echinococcus has been opened and laid back in five parts, so that the surface of the bladder worm may be seen, with the brood capsules, visible to the naked eye, showing through it. Natural size. (After Leuckart.)
An echinococcus is a spherical or roundish bladder full of a watery liquid, which originates by liquefaction of the oncosphere, and in man may attain the size of a child’s head, but remains smaller in cattle (the size of an orange or apple). The thin wall of the bladder is composed of an external laminated cuticle (ectocyst) and an internal germinal or parenchymatous layer (endocyst). The latter again
Fig. 252.
Figs. 252 and 252A.—Diagrams of mode of formation of brood capsule and scolices. (1) Wall of mother cyst, consisting of ectocyst and endocyst; (2) theoretical stage of invagination of wall; (3) a brood capsule with the layers of the wall in the reverse position to that in the mother cyst; (4) evagination of wall; (5) invagination; (6) fusion to form the solid scolex; (7) invagination of fore-part of scolex into hind-part. (Note.—The size of the scolex is much out of proportion to the brood capsule.) (Stephens.)
Fig. 252a.
The development in cattle often remains stationary at the bladder stage, and they are then called “acephalocysts,” or Echinococcus cysticus sterilis. According to Lichtenheld, sterile cysts occur in 80 per cent. of cases in cattle, in 20 per cent. in pigs, and in 7·5 per cent. in sheep. In other cases large numbers of small, hollow BROOD CAPSULES are formed in the germ layer, but are not arranged in any particular order. The order of the layers is just the reverse in them to what it is in the parent cyst, that is to say, they have inside a thin non-laminated cuticle and the parenchymatous layer on their external surface. These, theoretically at least, may be regarded as invaginations of the bladder wall giving rise to a cavity with the cuticle internal and the parenchymatous layer external. If we suppose the orifice to close, we should then get an isolated cavity with cuticle internal and parenchymatous layer external, as in the brood capsule (fig.252). If we next suppose an evagination of the wall of the brood capsule to occur at one point we should get a hollow process lined with cuticle; at the bottom of this we get the scolex and hooklets formed, and a little higher up the tube the suckers (fig.252, 4). If this hollow scolex is now pictured as being invaginated we get a hollow scolex covered with cuticle and lined by a parenchymatous layer projecting into the cavity of the brood capsule. The two sides of this hollow scolex now fuse and we get a solid scolex projecting into the cavity. Finally, if we imagine once more the rostellum and suckers invaginated into the posterior part of the scolex we get the condition as frequently found in the brood capsules, i.e., a scolex covered with cuticle projecting into the cavity, with the rostellum and suckers invaginated into the posterior portion of the scolex (fig.252A, 7).
Fig. 253.—Section through an invaginated echinococcus scolex. Cf. fig.252A, 7. ×300. (After DÉvÉ.)
A large hydatid may contain many thousands of brood capsules. Each brood capsule is about as big as a pin’s head, and may contain ten to thirty or more scolices. The delicate wall of the brood capsules may rupture, so that the scolices are now free in the mother cyst. These free scolices and also free brood capsules constitute what is known as “hydatid sand,” which settles at the bottom of a glass when hydatid fluid is poured into it. This form occurs chiefly in domesticated animals and is termed E. veterinorum, Rud., or E. cysticus fertilis.
In man, and only rarely in cattle, the mother cyst first forms “daughter cysts” (E. hominis, Rud. [fig.255]), which, though smaller than the “mother cyst,” resemble it in the structure of their walls; thus they are covered externally by a laminated cuticle and internally by the parenchymatous layer. They originate:
(1) Between the laminÆ of the cuticle of the mother cyst from small, detached portions of the parenchymatous layer; during their growth they bulge inwardly or outwardly and may separate themselves entirely from their parent cyst. In the latter case they lie between the mother cyst and the capsule of connective tissue formed by the host (E. granulosus or E. hydatidosus exogenus); when growing inwardly they reach the interior of the mother cyst (E. hydatidosus endogenus). Their number is very variable and does not depend on the size of the mother cyst. They are as big as, or bigger than, gooseberries.
Fig. 254.—A piece of the wall of an Echinococcus veterinorum stretched out and seen from the internal surface. A few brood capsules (the outline of which is only faintly shown), with scolices directed towards their interior and exterior. 50/1.
(2) According to some authors, endogenous daughter cysts arise also
Fig. 255.—Echinococcus hominis in the liver. The fibrous capsule and the wall of the echinococcus have been incised, so that the endogenous daughter cysts may be seen. Reduced. (After Ostertag, from Thoma.)
Fig. 256.—Section through an echinococcus scolex in process of vesicular metamorphosis, twenty-six days after insertion in the pleural cavity. ×250. (After DÉvÉ.)
(3) Transformation of Brood Capsules into Daughter Cysts.—This is also held to be possible by various observers. New epithelial layers are deposited between the cuticle which lines the brood capsule and the outer parenchymatous layer. This parenchymatous layer gradually disappears and a new parenchymatous layer forms in the interior from the parenchyma of the scolex or scolices. Although it appears strange that a completely formed scolex with specifically differentiated tissues and organs should retrogress to more primitively organized matter, and again become a proliferating bladder, yet we can hardly doubt that the older observations, regarding such a vesicular metamorphosis, of Bremser (1819), v. Siebold (1837), Naunyn (1862), Rasmusser (1866), Leuckart (1881), Alexinsky (1898), Riemann (1899), DÉvÉ (1901), and Perroncito (1902) are correct.
(4) Further, a fourth method of formation of daughter cysts is described by Naunyn as occurring in sterile hydatids, i.e., those containing no brood capsules. In this case a portion of the mother wall of the hydatid gets constricted off.
Fig. 257.
Figs. 257 and 257a.—Diagram of transformation of a scolex into a daughter cyst (1 to 3): 1, scolex in brood capsule; 2, liquefaction of scolex; 3, daughter cyst; and (4 to 6) of a brood capsule into a daughter cyst; 4, brood capsule with scolex; 5, deposition of new epithelial layers on the inner layer of the parenchyma; 6, disappearance of outer parenchyma and formation of inner parenchyma from the parenchyma of scolex, which has now disappeared. (Note.—The scolices are out of proportion to the brood capsules and to the daughter cysts. Stephens.)
Fig. 257A.
It has also been established that not only daughter cysts transplanted into animals develop further (Lebedeff, Andrejew, Stadnitzky, Alexinsky, Riemann), but that this also holds good if only hydatid scolices from
The echinococcus fluid, which originally is formed from the blood of the host, is light yellow, with a neutral or slightly acid reaction; its specific gravity averages 1009 to 1015. It contains about 1·5 per cent. of inorganic salts, half of which is common salt; in addition (besides water) it contains sugar, inosite, leucine, tyrosin, succinic acid (associated with lime or soda) and albumens which are not coagulated by heat; occasionally also the fluid has been found to contain hÆmatoidin and uric acid salts (in echinococcus of the kidneys), which doubtless demonstrates that the echinococcus liquid originates from the host. It has been generally assumed that echinococcus fluid contains a toxic substance the escape of which into the body cavity (at operation or by bursting of a hydatid cyst) produces more or less severe symptoms (fever, peritonitis, urticaria), so much so that one speaks of hydatid intoxication. The
According to the researches of Leuckart, the growth of the echinococcus is very slow; four weeks after infection the average size is only 0·25 to 0·35mm., at the age of eight weeks it is 1 to 2·5mm., and at this period the formation of the central cavity commences; at the age of five months, and with a size of 15 to 20mm., the first brood capsules with scolices are formed. The consequence of this gradual increase of size is that the organ attacked can maintain its functions by vicarious hypertrophy, and that many echinococci induce no special symptoms and cannot even be diagnosed, the latter circumstance being due to their hidden position.
The echinococcus cannot be said to be scarce in man, as is shown by the following table for Central Europe:—
| Place | Period | No. of post-mortems | No. of cases of echino. | Percentage |
| Rostock | 1861–83 | 1,026 | 25 | 2·43 |
| Greifswald | 1862–93 | 3,429 | 51 | 1·48 |
| Jena | 1866–87 | 4,998 | 42 | 0·84 |
| Breslau | 1866–76 | 5,128 | 39 | 0·761 |
| Berlin | 1859–68 | 4,770 | 33 | 0·69 |
| WÜrzburg | — | 2,280 | 11 | 0·48 |
| GÖttingen | — | 639 | 3 | 0·469 |
| Dresden | 1852–62 | 1,939 | 7 | 0·36 |
| MÜnich | 1854–87 | 14,183 | 35 | 0·25 |
| Vienna | 1860 | 1,229 | 3 | 0·24 |
| Prague | — | 1,287 | 3 | 0·23 |
| Kiel | 1872–87 | 3,581 | 7 | 0·19 |
| ZÜrich, Basle, Berne | — | 7,982 | 11 | 0·13 |
| Erlangen | 1862–73 | 1,755 | 2 | 0·11 |
These, however, are only cases that have become known by post-mortem; in addition, there are cases that have been treated medically, of which there are a few statements, at all events relating to the principal districts of Germany. According to Madelung, one case of echinococcus occurs in every 1,056 inhabitants in the town of Rostock, in the district of Rostock one to every 1,283, in Schwerin one to every 5,887, and in Ludwigsort one to every 23,685; according to Peiper, in Upper Pomerania one case occurs to every 3,336, in the district of Greifswald one to every 1,535 inhabitants. The northern districts of Pomerania are more affected than the southern ones.
Accordingly, echinococcus is also considerably more frequent in cattle in Pomerania. On an average in Germany 10·39 per cent. oxen, 9·83 per cent. sheep, and 6·47 per cent. pigs are infected, whereas in Upper Pomerania 37·73 per cent.
Fig. 258.—Hooklets of echinococcus. a, of Echinococcus veterinorum; b, of TÆnia echinococcus, three weeks after infection; c, of the adult TÆnia echinococcus; d, the three forms of hooklets outlined one within the other. 600/1. (After Leuckart.)
Beyond the European continent, echinococcus is frequent in the inhabitants of Iceland, Argentine, Paraguay and Australia. In Iceland, according to Finsen, 1 in every 43 inhabitants is affected with echinococcus; according to Jonassen the proportion is 1 to 63; this is due to the habits of the people of Iceland or, in fact, to the frequency of TÆnia echinococcus in dogs, and the prevalence of the hydatid in cattle. In certain districts of Australia it is just as frequent. In Cape Colony, Egypt and Algeria echinococcus is not rare, but it is scarce in America and in Asia, with the exception of the nomadic tribes of Lake Baikal.
Echinococcus attacks persons of every age, though it is rare in children up to 10 years of age and in old people. It occurs most frequently between the ages of 21 and 40 years. According to all statistics it preponderates in women (about two-thirds of the cases). The liver is its favourite seat (57·1 per cent. of the cases); next in order come the lungs (8 per cent.), kidneys (6 per cent.), cranial cavity, genitalia, organs of circulation, spleen (3·8 per cent.), etc. As a rule one organ only is invaded; multiple occurrence may originate from one infection, or eventually from a later infection (?), or it may come to pass that from some cause (through the spontaneous rupture of an echinococcus, or the rupture of one caused by an injury or surgical operation) daughter cysts, brood capsules or scolices escape into the abdominal cavity,294 where they settle or become transformed and go
Human echinococci may also die at various stages of development, become caseous or calcified, or may be absorbed, the cause for this being either disease of the hydatid itself or inflammation of its connective tissue capsule; the discovery of the laminated cuticle, which has great powers of resistance, or the finding of the hooklets of the scolices is sufficient to form a conclusion as to the nature of such formations.
Siebold (1853) was the first to rear TÆnia echinococcus in the dog by feeding it with the echinococcus of cattle and especially of sheep. KÜchenmeister, van Beneden, Leuckart, Railliet and others obtained similar results, and Thomas, Naunyn, Krabbe and Finsen succeeded in rearing T. echinococcus in dogs from the bladder worms of human beings; these grow comparatively slowly (one to three months295) and only during the process of growth develop their hooklets in their definite form (fig.258). It lies in the nature of things that dogs, whether experimentally or naturally infected, almost always harbour T. echinococcus in large quantities. That cats exceptionally harbour these worms has been already mentioned (DÉvÉ). Finally, Leuckart infected young pigs by feeding them with mature segments.
Echinococcus multilocularis (alveolar colloid).
In addition to the form of echinococcus already described, and which is also frequently termed Echinococcus unilocularis, there is a second form which occurs in man as well as in animals, and which is termed E. multilocularis, s. alveolaris (alveolar colloid).
It was originally regarded as a tumour; its animal nature was first established by Zeller and R. Virchow. The parasite, which varies in size from that of a fist to a child’s head, presents a collection of numerous cysts, measuring between 0·1 and 3 to 4mm. to 5mm. in diameter, which are embedded at first in a soft, connective tissue stroma; the cut surface has therefore a honeycomb appearance. The cysts are surrounded by a pellucid and laminated cuticle, and each according to its size encloses either a small-celled tissue or a cavity lined by a parenchymatous layer; the fluid contained in such a cavity may be transparent, or is rendered opaque by globules of fat, bile-pigment, hÆmatoidin and fat crystals. According to some authors all or most of these cysts intercommunicate; others state that this is the case at least as regards the cuticle. The scolices are by no means
One circumstance is peculiar to the multilocular echinococcus of man, namely, the disintegration that sets in at certain stages; in the centre of the parasite a cavity forms that frequently becomes very large and is filled with a purulent or brownish or brownish-green viscid fluid; in this fluid one finds shreds of the wall of the cavity, calcareous bodies, echinococcus cysts, also scolices and hooklets, as well as fat globules and crystals of hÆmatoidin, margarine and cholesterin and concretions of lime. Such ulcerative processes, according to Ostertag, are never present in the multilocular echinococcus of oxen,296 in which the separate cysts are larger and the connective tissue integument less powerfully developed.
Fig. 259.—Echinococcus multilocularis in the liver of the ox. Natural size. (After Ostertag.)
Hardly anything positive is known with regard to the development of the alveolar echinococcus; its peculiar conformation is attributed by some to enormous infection of oncospheres, by others to the abnormal situation of one oncosphere; a few authors ascribe it to infection of lymphatic vessels, others to infection of the biliary ducts or to peculiarities of the surrounding hepatic tissue; Leuckart ascribes it to a grape-like variety of form which continues budding; a few more recent authors consider multilocular echinococcus to be specifically different from unilocular echinococcus, and therefore also different the species of TÆnia arising from them. Melnikow-Raswedenkow is also of this opinion. According to this author the oncospheres infect the lumen of a branch of the portal vein in
The multilocular echinococcus, which in man produces a severe disease and almost always leads to premature death, infects most frequently the liver, but may also be found primarily in the brain, the spleen and the suprarenal capsule; from the liver by means of metastasis it may reach the most various organs, especially those of the abdomen, but also the lungs, the heart, etc. Up to 1902, 235 cases have been described and up to 1906, 265, being 70 from Russia, 56 from Bavaria, 32 from Switzerland, 30 from the Austrian Alps, 25 from WÜrtemberg; the remaining cases are distributed over Central Germany, Baden, Alsace, France, Upper Italy, North America. In some the origin is doubtful; in any case after Russia, the mountainous South of Europe is the principal region of distribution. As to the domesticated animals, the same parasite is found principally in the ox (according to Meyer, in Leipzig, in 7 per cent. of the oxen affected with echinococcus); it is rarer in the sheep and very scarce in the pig.
It has already been mentioned above that recently the multilocular echinococcus has been stated to be specifically different from hydatid or unilocular echinococcus. To this may be added the fact that Mangold, who fed a young pig with oncospheres of a TÆnia reared from the multilocular echinococcus, found two growths in the liver four months later, which he took to be E. multilocularis, and consequently one has to assume the existence of two different worms. The chief defender of this view, already put forward by Vogler, Mangold, and MÜller, is Possett. He bases his opinions on (1) the more restricted distribution of the multilocular hydatid, the former occurring in districts where only cattle are raised, the latter where sheep-breeding is established; (2) that those engaged in looking after sheep are attacked by multilocular, whereas those looking after cattle are attacked by unilocular hydatid; (3) that among the cases of unilocular hydatid occurring in the distribution areas of multilocular hydatid no transitions between the two forms are observed; (4) on the difference in the hooks both in the hydatid as well as in the TÆnia
Serum Diagnosis of Echinococcus.
(1) Precipitin Reaction.—Mix equal parts of hydatid fluid (of the sheep) and serum of patient. Keep at 37°C. The reaction is not decisive as it may be given by normal sera.
(2) Complement Deviation.—Required: (1) Hydatid fluid of sheep (antigen), (2) guinea-pig complement, (3) patient’s serum, (4) red cells of sheep, (5) hÆmolytic serum (of rabbit) against sheep’s red cells, (6) 0·8 per cent. salt solution. Mix the antigen + patient’s serum (heated) + complement + salt solution at 37°C. for one hour. Add red cells of sheep + hÆmolytic serum. Allow to stand for half an hour at 37°C. It is imperative to make adequate control observations. An example will indicate the method. Salt solution 1·3c.c. + patient’s serum (heated) 0·2c.c. + hydatid fluid 0·4c.c. + complement 0·1c.c. of serum diluted to a quarter strength + hÆmolytic serum and red cell emulsion 1c.c. Result: no hÆmolysis, i.e., the patient’s serum contains specific (echinococcus) antibodies.
C. NEMATHELMINTHES.
BY
J.W.W. STEPHENS, M.D., B.C., D.P.H.
Bilaterally symmetrical animals, without limbs and with a body cavity in which the gut or other organs float. They are generally cylindrical.
Class. NEMATODA.
Nemathelminthes with an alimentary canal.
Nematodes are as a rule elongated round worms of a filiform or fusiform shape; their length varies according to the species from about 1mm. to 40 to 80cm. The outer surface of the body is smooth or annulated, and at certain points provided with papillÆ, occasionally also with bristles and alar appendages. The anterior end carrying the oral aperture is usually rather slender, occasionally quite thin; the posterior end is pointed or rounded; the anus, as a rule, lies somewhat in front of the posterior extremity. The sexes are almost always separate, and the male can as a rule be easily distinguished from the female because the former is smaller and more slender, its posterior extremity is often spiral or incurved, or carries an alar appendage, whereas the female is larger and thicker, and its posterior extremity is straight. In the male the genitalia open into the anus; the sexual orifice of the female opens ventrally along the median line in the anterior half of the body, in the middle, or a little further back. Both sexes, moreover, have an orifice, the excretory pore, which is situated ventrally in the median line and about the level of the oesophageal nerve ring.
In large species, even with the naked eye, two lighter transparent bands—the lateral lines—may be distinguished; they run along the sides of the body from the anterior to the posterior end, while two other bands, the median lines, running along the ventral and dorsal mid-lines, are less evident; in exceptional cases there are also four sub-median lines. These bands or lines are inward projections of the ectoderm, and in them lie the nerves and excretory vessels (fig.260).
Some Nematodes live free in fresh or salt water, in soil, mud or decaying vegetable matter, others parasitically in the most various organs of animals, frequently also in plants.
Anatomy of the Nematodes.
All the Nematodes are covered by (1) a CUTICLE, which in the small species is thin and delicate, while in the larger species it is thickened, and may consist of several layers of complicated structure. Canalicular pores do not occur. According to general opinion, which is confirmed by the history of development, the cuticle is a product of (2) the EPITHELIUM or ectoderm that had formerly existed or is still found beneath it; in young specimens and small species it is perceptible, but in older worms it frequently alters so considerably
Fig. 260.—Diagram of a transverse section of Ascaris lumbricoides, showing thick cuticle, and beneath it the matrix or syncytial ectoderm. The flat intestine is in the middle, and to the right and left near it in the body wall the lateral lines with excretory vessel and lateral nerves; above and below in the centre the dorsal or ventral median lines with the nerves radiating to the muscles, also the muscle cells with their striated outer contractile portion and inner nucleated vesicular protoplasmic portion. About 50/1. (After Brandes.)
Unicellular cutaneous glands are known in parasitic as well as in free-living species; they vary in number and arrangement, and are found discharging some at the anterior extremity and others in the vicinity of the genital orifices. In other cases large numbers of them are present along the lateral lines; they are strongly developed in most of the TrichotrachelidÆ, where they discharge either along a part of the ventral surface or along the lateral and median lines; they are placed so closely together that the ridges of the cuticle perforated by the orifices have long been known, and have been described, as “rodlet borders,” or “fields of rods.”
As the cutis is immediately adjacent to (4) the DERMO-MUSCULAR TUBE the simple layer of the muscular cells is divided into four quadrants by the longitudinal lines—two dorsal and two ventral (fig.260). The MUSCLES are in the simplest cases large rhomboid cells that lie two by two in each quadrant, so that on transverse section of the entire worm only eight cells are perceptible. The outer border of the cells is converted into contractile fibrils, while the contiguous inner portion has remained protoplasmic, and contains the nucleus. In large species the muscular cells do not only increase in length (up to 3mm.) and in number in every quadrant, but their contractile portion curves up to form a groove (like that of a dead leaf) thereby even becoming thicker; simultaneously space is gained for more cells, the protoplasmic parts of these cells (on transverse section) project out of the grooves like vesicles. In all cases there is only one layer of longitudinal muscular cells, which, by contracting, can shorten the body or, by contracting one side, can bend it. In the latter case the muscles of the opposite side have an antagonistic effect, or when all the muscles are contracted, the elasticity of the cuticle acts in the same way. Special muscles exist at the beginning of the gut and at sections of the genital apparatus.
The existence of a cavity between the body and the gut wall has hitherto been generally assumed, and has been referred to the cleavage cavity, and consequently designated as a primary body cavity. More
Fig. 261.—Anterior end of an Ascaris megalocephala cut open and showing the four tuft-like organs lying on the lateral lines. Natural size. (After Nassonow.)
We may now consider the “tuft-like” or “phagocytic” organs, which attain 1cm. in size, and consist of four, six, or even more ramified cells, which lie close to the walls of the body (fig.261). They are found either only in the anterior part of the body (Ascaris), or throughout the whole length of the body (Strongylus, syn., Sclerostomum), and their position usually corresponds to the lateral lines. In some species there are small protoplasmic cells on the processes of these organs. In consequence of their size they can be recognized with the naked eye, especially when they are loaded with granules of stain (carmine, Indian ink) injected into the body cavity.
Intestinal canal.—The oral aperture, which is situated at the tip of the anterior extremity, is frequently surrounded by thick lips, or small bristles, or papillÆ; it leads to a more or less strongly developed buccal cavity, which is lined by a continuation of the body cuticle, and which in some species is provided with “teeth,” representing differentiated portions of the cuticle.
The oesophagus (fig. 262), which arises from the base of the oral cavity, is as a rule a short, bottle-shaped tube with triradiate lumen; its wall is chiefly composed of radiating muscular fibres, which give it the appearance of being transversely striped when viewed from the surface. There exist also in its wall three large gland cells (oesophageal glands) and nerves arising from the lateral lines and running forward. The radial fibres cause a dilatation of the lumen, and exercise an effect antagonistic to the elasticity of the cuticle lining the inner surface. The latter has its own particular layer, which is not in direct connection with that of the oral cavity. Special dilator muscles, arising from the dermo-muscular tube and situated at the commencement of the oesophagus, are only known in a few species. The posterior end of the oesophagus presents a bulb-like dilatation, and is frequently provided with small chitinous movable valves. In a few forms, which belong to the TrichotrachelidÆ (Trichocephalus, Trichinella), the oesophagus is a very long cuticular tube, beset on its dorsal surface with a series of large nucleated cells. In others (Cucullanus, Ascaris, etc.), a tube, the so-called glandular stomach, lined only by epithelial cells, follows behind the muscular oesophagus. This glandular stomach is, from its structure, easily distinguished from the mid-gut, or chyle intestine, which is likewise cellular. The so-called mid-gut is a tube lined by flat, cubical, or cylindrical cells (fig.260) surrounded by “isolation tissue”; its transverse section is circular or flattened dorso-ventrally; the lumen may run in a straight line, or it runs a sinuous course through the alternating prominences of the then flat epithelial cells.
The ectodermal hind gut is, as a rule, very short. At the anal opening the cuticle and the subcuticular layers are reflected inwards, forming the lining of the hind gut. In large species the subcuticular tissue forms large cells on which anteriorly lie in addition large “glandular cells.”298 In the male the ejaculatory duct opens at this point. Around the end part of the gut, either on the chyle intestine or at the beginning of the end gut, there exists a sphincter muscle arising from a muscle cell which acts antagonistically to the two diaphragm-like dilator muscle cells which stretch from the gut to the
Intestinal cÆca and oesophageal glands sometimes exist as intestinal appendages; the former are tubular appendages of various size, running backwards or forwards, and arising from the posterior extremity of the oesophagus. They are lacking in many species. The oesophageal glands are unicellular; a dorsal and two subventral glands may be distinguished according to their position; as a rule they open into the oesophagus at a distance from one another. The body of the gland lies in the bulb of the oesophagus, or in the dorsal cul-de-sac arising from it.
Fig. 262.—Transverse section through Ascaris lumbricoides at the level of the oesophagus behind the nerve ring. Cu., cuticle; Sc., subcuticular layer; Ex., excretory vessel; Is., isolation cell and the system of lamellÆ proceeding from it; M., muscles; Ml., median line; Sl., lateral line. Magnified. (After Goldschmidt.)
The nervous system is sufficiently known in a few species only; it consists of a ring containing fifty to sixty fibres closely surrounding the oesophagus, various groups of ganglion cells, and a certain number of nerves extending anteriorly as well as posteriorly. The remarkably small number of fibres, as well as ganglion cells, is characteristic of the nervous system of all Nematodes. Immediately behind the oesophageal ring (fig.263, Lg.) an agglomeration of ganglion cells lies at either side (lateral ganglia); part of their off-shoots form the oesophageal ring, and part are directed posteriorly and ventrally, and unite partly in front of and partly at the back of the excretory pore, with fibres originating direct from the oesophageal ring, and passing along the ventral median line to the back; these fibres then together form the ventral median nerve (fig.263, V.m.n.). This nerve, originally consisting of thirty to fifty fibres, becomes in the female attenuated quite evenly in its further course. There is also an agglomeration of ganglion cells close in front of the anus (anal ganglia), and then the median nerve divides in order to combine with
Fig. 263.—Schematic representation of the nervous system of a male Ascaris megalocephala. A., anus; Ag., anal ganglion; C., commissures; D.m.n., dorsal median nerve; Exp., excretory pore; Pr., oesophageal sensory ring; Lg., lateral ganglia; Ln., lateral nerve; Sp., papilla; V.m.n., ventral median nerve. (After Brandes.)
In the male each ventral part of the lateral nerves becomes thickened by taking up fibres from the ventral nerves, which become thickened posteriorly to the nervus bursalis, which towards the middle gives off a mass of fibres to the “genital papillÆ” situated in front of and behind the anus; the number of these fibres averages eighty to 100; in its further course the bursal nerve resembles the corresponding ventral part of the lateral nerves of the female.
The ventral and dorsal nerves are connected by a number of semicircular commissures, which originate from the ventral nerves and serve to supply the dorsal nerve, which is always being decreased by fibres departing from it. It is remarkable that these commissures are not placed symmetrically, and their position also is different in the two sexes; in the female there are thirty-one on the right side and only thirteen on the left side. In the male there are thirty-three commissures on the right side and fourteen on the left, which run into the subcuticular layer, generally in pairs, and usually cross at the level of the lateral lines.
The fibres of the two median nerves are chiefly motor; fascicular processes run from each protoplasmic part of the muscular cells to the median nerves; from these they take up bundles of primitive fibrils, which separate, pass through the protoplasmic part and enter the contractile part (fig.260). One part of the fibrils, however, penetrates beyond the muscles into the subcuticular layer, where they form a network, probably of a sensory nature, with contiguous fibrils. Nerves directed anteriorly finally originate from the oesophageal ring; they consist each of three fibres, carry three ganglion cells at their point of origin, and enter the sensory organs of the three papillÆ surrounding the oral aperture. Two of these little trunks lie in the lateral lines, the remaining four are situated in the middle of the four quadrants (Nn. sub-mediani anteriores).
Parasitic species lack higher ORGANS OF SENSE; free-living worms occasionally have two rust-red eyes, sometimes with lenses, at the anterior part of the body. In addition to the above-mentioned sensory papillÆ surrounding the oral aperture and the genital papillÆ of the male at the end of the body, another pair exist in the vicinity of the lateral ganglia, the “cervical papillÆ,” and two dorsal papillÆ in the central region of the body and two lateral ones near the tip of the tail (AscaridÆ). The differences in the distribution and number of the sensory papillÆ serve for characterizing the larger and smaller groups of Nematodes.
The excretory organs of the Nematodes are variable. In a great many cases the apparatus is symmetrical, and consists of a vessel commencing in the posterior extremity in each lateral line (fig.260), and passing anteriorly. In the vicinity of the anterior extremity both
This excretory vesicle is a single elongated or horse-shoe-shaped cell, with a large nucleus and an intracellular tubular system, which is connected with the excretory duct arising from the excretory pore on the outer surface (fig.326). The so-called ventral gland is the only excretory organ of marine Nematodes, and probably represents a primitive form. Goldschmidt, who has investigated the excretory apparatus of Ascaris lumbricoides, considers that the vessels running in the lateral lines are only ducts to which belong a glandular system hitherto overlooked or otherwise interpreted. This system also lies in the lateral lines, and takes the form of two glandular tracts, forming a syncytial tissue in which lie the ducts, one dorsal, one ventral. In parts these tracts are connected by commissures, although their junction with the excretory vessels cannot be clearly made out. These statements, however, require confirmation. The author has further found that the anterior ends of the lateral canals, directly before they bend ventrally, anastomose with one another and give off anteriorly a small blind process, which can be interpreted as a rudiment of a canal coming from the head end, and as a matter of fact, according to Golowin, such anterior excretory canals exist in a number of genera.
In a number of Nematodes (Cheiracanthus, Capillaria, Trichocephalus, Trichinella, etc.), however, special excretory organs are lacking; possibly the cutaneous glands, which are in these species generally powerfully developed, replace these organs.
Sexual organs.—With the exception of a few species, the Nematodes are sexually differentiated.
(a) Female Sexual Organs.—The sexual orifice (vulva), surrounded by thick labia, is, as a rule, ventral and varies in position from near the
Fig. 264.—Diagram of female genitalia. Ov., ovary (in part); Ovd., oviduct; Rec. sem., seminal receptacle; Ut., uterus (in part); Ovj., ovejector; Vag., vagina.
Fig. 264a.—Diagram of male genitalia of a strongylid. Test., testis (in part); S.V., seminal vesicle; c.g., cement gland surrounding ejaculatory duct; sp., spicules; cl., cloaca; gub., gubernaculum; p.p.a., pulvillus post-analis; g.c., genital cone; l.d., dorsal lateral line; l.v., ventral lateral line (the bursa is not shown).
Fig. 265.—Transverse section through the ovarian tube of Belascaris cati of the cat at various levels. To demonstrate the development (right to left) of the ova and of the rhachis. Magnified.
At the blind end of the ovary there is a mass of protoplasm with numerous nuclei that multiply continuously. Gradually the nuclei arrange themselves in longitudinal rows (fig.265) and the protoplasm commences to leave the periphery and surround each nucleus. The nearer to the uterus the more progressive is this loosening process, until club-shaped cells each containing a nucleus are developed. The most pointed end of each, however, is still attached to an axial fibre of protoplasm, the rhachis; probably this has some connection with the nutrition of the ova. Finally the ova fall off and reach the uterus, where they are fertilized and enclosed in shells.
(b) Male Sexual Organs.—There is never more than one testis (fig.266), which is a straight or sinuous tube of the same construction as an ovary, and in which the mother cells originate in the same manner as the ova. In the same way as the ovary passes into the uterus, so does the testis pass into the spermatic duct; the latter is often divided into the somewhat dilated seminal vesicle and into the muscular ductus ejaculatorius, which, running ventral to the intestine backward (fig.267), finally opens into the cloaca. In many species, e.g., A. duodenale, the ejaculatory duct is surrounded for a greater or less portion of its extent by the cement gland, the secretion of which (brownish or blackish in colour) serves for copulation. The ejaculatory duct of the large AscaridÆ is for the most of its course surrounded by a muscular network which takes its origin from the two dilator cells of the gut (fig.268 F.). The spermatozoa of the Nematodes, it may be noted, only attain their full development after the sperm mother cells have been conveyed by copulation into the uteri of the female genitalia. In their form (sheathless, capable of amoeboid motion) they differ from those of most other animals.
Spicules.—The male genital apparatus is also provided with one or two sacs, situated on the dorsal side of the intestine, and opening into the cloaca. In each sac there is a chitinous rod-like body, the spicule. Further, in many cases there exists, more or less fixed in the dorsal wall of the cloaca, a chitinous structure, the accessory piece or gubernaculum, the latter name implying its function of guiding the spicules during copulation (fig.264A). A special muscular apparatus,
Fig. 266.—Male of the rhabditic form of Angiostomum nigrovenosum. A., anus; I., mid-gut; T., testicular tube; O., oral orifice; P., papillÆ; Sp., spicule. Magnified.
Fig. 267.—Transverse section through the posterior extremity of the body of Ascaris lumbricoides (male). The intestine is in the middle, and the lateral lines are subjoined thereto; above the intestine the two spicule sacs are seen; below is the ductus ejaculatorius. The muscular fibres are between the lateral and median lines. Magnified.
Bursa copulatrix.—The males in many genera possess epidermal wing-like appendages at their posterior extremity. These are supported by elongated tactile papillÆ called ribs. In the most highly developed bursÆ, e.g., in the StrongylidÆ, the ribs are called rays, as they consist not only of nerve fibres but mainly of “pulp,” i.e., prolongations of the subcuticular layer. BursÆ are either open, i.e., bilaterally symmetrical, or closed, when the posterior border is continuous all round. A pseudo-bursa is one unsupported by ribs or rays, e.g., in Trichuris. The bursa serves as an organ of prehension during copulation. Some forms, moreover, carry a sucker at the posterior extremity (e.g., Heterakis); in others the spicules and other prehensile organs are absent; they are then replaced by an evertible cloaca, e.g., Trichinella.
Development of the Nematodes.
After impregnation, the ovum develops around itself a delicate membrane (vitelline membrane), and subsequently an egg-shell is formed. This is derived either as a secretion from the uterine wall or it is a further differentiation of the vitelline membrane, the original single membrane splitting into two, the outer becoming the egg-shell. Further the uterus often secretes a special albuminous covering around the egg-shell. The “yolk” granules of the ovum are secretions of the protoplasm of the ovum itself and first appear when the rhachis is formed. In certain cases ova lie in follicles or capsules formed of epithelium cells derived from the ovarian tubes. These cells subsequently fuse and form a membrane—the CHORION.
Fig. 268.—Hind end of a male Ascaris lumbricoides cut across at the level of the dilator cells of the gut. D., gut; Dil., dilator cells of the gut; F., a process of the dilator cells forming a network over the vas deferens; Sl., lateral line; Sp., spicule; Vd., vas deferens. The anterior end of the worm lies to the right. Magnified. (After Goldschmidt.)
The shape of the completed eggs is characteristic of the different species, and therefore a single egg often suffices to diagnose the species. According to the species, the eggs may be deposited sooner or later, either before or during segmentation, or with the embryo perfectly developed. Only a few species are viviparous, e.g., Dracunculus mediensis, Trichinella spiralis; in the other Nematodes the further development of the extruded eggs takes place after various
Finally, a nematode-like embryo develops, which usually lies somewhat coiled up within the shell, and varies in its further development according to the species to which it belongs.
In the simplest forms, as in the free-living Nematodes, the embryos, apart from their size, resemble their parents, and grow up into these after leaving the egg-shell. In many parasitical Nematodes, however, the young must be called larvÆ, as they present characters which are subsequently lost.
The manner of conveyance of the eggs or the embryos contained in them after they have left the body into the definite host is very different in the various species.
(1) Without Intermediate Host.—(a) In many the conveyance into the definite host is effected directly after the larvÆ have developed within the eggs; thus, for instance, the feeding of suitable animals with the embryo-containing eggs of species of Trichocephalus and Ascaris leads to an infection of the gut, for the young Trichocephali or Ascarides only leave the egg-shell when they have attained the intestine of the final host, in which they become adult.
In other cases (b) Ancylostoma, Necator, the larvÆ hatch in the open, and live for a time free, changing their form; they grow, cast their skin, and finally gain the intestine of the host by means of water or through the skin, when they lose their larval characters and assume the structure of the adult worm.
(c) In a number of Nematodes, however, HETEROGONY occurs. This terms signifies a mode of development in which two structurally different sexual generations of the same species alternate with each other. To these appertains, for instance, Angiostomum (syn.: Rhabdonema) nigrovenosum, which lives in the lungs of frogs and toads; this Nematode measures about 1cm. in length and is hermaphrodite (protandric). The eggs are deposited in the pulmonary cavity, and through the cilia of the same reach the oral cavity, where they are swallowed and thus conveyed into the intestine. They pass through the entire gut, and are finally evacuated with the fÆces; often, indeed, the young themselves emerge from the egg-shell within the hind-gut of the frogs. These young forms become sexually differentiated, remain much smaller than the parent, their oesophagus is differently constructed (rhabditis form), and they are non-parasitic (fig.266). After having grown in the open they copulate; the males die soon after copulation, and the females in their own bodies develop a few young, which, given the opportunity to get into frogs, infect them, and are transformed into the hermaphroditic Angiostomum.
Fig. 269.—A piece of the trunk muscle of the pig with encapsuled embryonic TrichinÆ. Magnified.
(2) With Intermediate Host.—(a) Frequently, however, the larvÆ of Nematodes make use of one or even two intermediate hosts; their condition then resembles that of Cestodes or Trematodes, excepting that there is never a multiplication within the intermediate hosts. The larvÆ become encapsuled amongst the tissues of the intermediate host, and wait till they are introduced with the latter into the final host. For instance, Ollulanus tricuspis, the adult form of which is found in cats, previously lives encysted in the muscular system of mice. Cucullanus elegans, which attains the adult stage in fishes (perch, etc.), is found encysted in species of Cyclops. Other examples of species that require an intermediate host are Filaria bancrofti and Dracunculus medinensis.
Peculiar conditions prevail in the case of (b) Trichinella spiralis. This species, which in its adult state lives in the intestine of man and of various mammals, is viviparous; the young TrichinÆ, however, do not leave the intestine, but reach the intestinal wall (Cerfontaine, Askanazy) in the following way: the female intestinal TrichinÆ bore into the intestinal wall, where they are found in the submucosa, or in the lumen of the dilated lacteal vessels. Here the young are born, in the intestinal wall, and leave this position with the lymph stream. Some of them, no doubt, actively bore through the intestinal wall, reaching the lymph or blood-stream, or even pass into the body cavity. What occurs during their further migrations is difficult to say at present. It has hitherto been maintained that the wandering is entirely active; for instance, the ligaturing of an artery would be no protection against the part of the body supplied by such artery being invaded by Trichinella. This observation cannot be otherwise explained than by the active progress of the young Trichinella. The question, however, may be mooted as to where and when the worms quit the blood-vessels, which they for the most part reach through
Classification of the Nematoda.
The Nematodes are usually divided into a number of families, some of which it is at present impossible to define accurately; moreover, the definition of many genera is also in an unsatisfactory state.
Family. AnguillulidÆ, Gervais and van Beneden, 1859.
A “family” name not definable. They comprise a vast number of small forms, most of which live free in fresh water, in soil, or in macerating substances; amongst them there are some which live parasitically on plants, more rarely on animals. They do not exceed 8mm. in length. The large majority are only 1 to 2mm., or even 0·5mm. The uterus is straight. Eggs in the uterus at one time, one to four. Genera very numerous, but many of them insufficiently defined (Anguillula, Anguillulina, Rhabditis, Heterodera, etc.).
Family. AngiostomidÆ, Braun, 1895.
Small Nematodes undefined morphologically, but characterized by heterogony, i.e., there is a free-living “rhabditic” generation and a parasitic “filariform” generation which succeed one another (e.g., Angiostomum, Strongyloides, Probstmayria).
Family. GnathostomidÆ.
Cuticle covered totally or partly with cuticular laminÆ fringed posteriorly with multiple points. Head subglobular, covered with simple spines. Two spicules. Vulva behind middle of body, parasitic in vertebrates, especially mammals (e.g., Gnathostoma, Tanqua, Rictularia).
Family. DracunculidÆ, Leiper, 1912.
Males very small in proportion to females. Anus absent. Vulva absent (?). Genera: Dracunculus, Icthyonema (in body cavity of eel and other fish).
Family. FilariidÆ, Claus, 1885.
Long thread-like Nematodes. Anus present. Œsophagus without bulb. Vulva usually in anterior half of body. Two ovaries. Generally ovoviviparous.
Family. TrichinellidÆ, Stiles and Crane, 1910.
Œsophagus consisting of a chain of single cells, the lumen of the oesophagus passing through their centre. Ovary single. Vulva at junction of anterior and posterior portions. Sub-families: (1) TrichurinÆ, (2) TrichinellinÆ.
Family. DioctophymidÆ.
Body anteriorly armed with spines or unarmed; mouth without lips, with six, twelve, or eighteen papillÆ in one or two circles; oesophagus very long without a bulb; anus terminal in female; one ovary; vagina very long; spicule in male very long; bursa cup-shaped without rays (Dioctophyme, Hystrichis, Eustrongylides).
Family. StrongylidÆ, Cobbold, 1864.
Bursa, supported by rays, always present. Oviparous.
Family. PhysalopteridÆ.
Mouth with two large lips. Bursa with supporting papillÆ in form of a lanceolate cuticular expansion, with genus Physaloptera.
Family. AscaridÆ, Cobbold, 1864.
Rather thick Nematodes. Mouth with three lips—one dorsal, two latero-ventral. Sub-families: (1) AscarinÆ, (2) HeterakinÆ, etc.
Family. OxyuridÆ.
Smallish forms, 4 to 45mm., with cuticle thickened on each side for the whole length of body in the form of a lateral flange or wing. Œsophagus long with a well-marked bulb containing a valvular apparatus. Tail end of female drawn out into a long point. Eggs asymmetrical. Males very small (about 2mm.). One spicule. Genera: Oxyuris, Passalurus, Ozolaimus, Atractis, etc.
MermithidÆ, greatly elongated “Nematodes,” which, in the larval stage, are parasitic in insects, but in their adult condition are free living. Cuticle with diagonal striation. Without an open mouth or anus. Oral papillÆ present. Characteristic eggs with two processes, ending in a tuft of filaments. LarvÆ with a movable boring spine at the head end.
GordiidÆ.—Long, thread-like “Nematodes.” Mouth and anterior portion of gut atrophied in adult. Oral papillÆ absent.
The Nematodes Observed in Man.
| Family | Sub-family | Genus | Species |
| AnguillulidÆ | — | Rhabditis | R. pellio. |
| R. niellyi. | |||
| Rhabditis sp. | |||
| Anguillula | A. aceti. | ||
| Anguillulina | A. putrefaciens. | ||
| AngiostomidÆ | — | Strongyloides | St. stercoralis. |
| GnathostomidÆ | — | Gnathostoma | Gn. siamense. |
| Gn. spinigerum. | |||
| DracunculidÆ | — | Dracunculus | D. medinensis. |
| FilariidÆ | FilariinÆ | Filaria | F. bancrofti. |
| F. demarquayi. | |||
| F. taniguchi. | |||
| F. (?) conjunctivÆ. | |||
| Group. | Agamofilaria | — | Ag. georgiana. |
| Ag. palpebralis. | |||
| Ag. oculi humani. | |||
| Ag. labialis. | |||
| F. (?) romanorum- orientalis. | |||
| F. (?) kilimarÆ. | |||
| F. (?) sp. ? | |||
| (Mikrofilaria) | Mf. powelli. | ||
| Mf. philippinensis. | |||
| Setaria | S. equina. | ||
| Loa | L. loa. | ||
| Acanthocheilonema | Ac. perstans. | ||
| Dirofilaria | Di. magalhÃesi. | ||
| OnchocercinÆ | Onchocerca | O. volvulus. | |
| TrichinellidÆ | TrichurinÆ | Trichuris | T. trichiura. |
| TrichinellinÆ | Trichinella | T. spiralis. | |
| DioctophymidÆ | — | Dioctophyme | D. gigas. |
| StrongylidÆ | MetastrongylinÆ | Metastrongylus | M. apri. |
| TrichostrongylinÆ | Trichostrongylus | T. instabilis. | |
| T. probolurus. | |||
| T. vitrinus. | |||
| HÆmonchus | H. contortus. | ||
| Mecistocirrus (Nematodirus) | M. fordi. | ||
| AncylostominÆ | |||
| Group. | ŒsophagostomeÆ | Ternidens | T. deminutus. |
| Œsophagostomum | Œ. brumpti. | ||
| Œ.stephanostomum var. thomasi. | |||
| Œ. apiostomum. | |||
| Group. | AncylostomeÆ | Ancylostoma | A. duodenale. |
| A. ceylanicum. | |||
| A. braziliense. | |||
| Group. | BunostomeÆ | Necator | N. americanus. |
| N. exilidens. | |||
| Group. | SyngameÆ | Syngamus | S. kingi. |
| PhysalopteridÆ | — | Physaloptera | P. caucasica. |
| P. mordens. | |||
| AscaridÆ | AscarinÆ | Ascaris | A. lumbricoides. |
| A. sp. | |||
| A. texana. | |||
| A. maritima. | |||
| Toxascaris | T. limbata. | ||
| Belascaris | B. cati. | ||
| B. marginata. | |||
| Lagocheilascaris | L. minor. | ||
| OxyuridÆ | — | Oxyuris | O. vermicularis. |
| MermithidÆ | — | Mermis | M. hominis oris. |
| (Agamomermis) | Ag. restiformis. |
Family. AnguillulidÆ.
Genus. Rhabditis, Dujardin, 1845.
Buccal cavity elongated, with lips. Its chitinous wall uniformly thick. Lateral lines absent. Males with bursa.
Rhabditis pellio, Schneider, 1866.
Syn.: Pelodera pellio, Schn., 1866; Rhabditis genitalis, Scheiber, 1880; Rhabditis pellio, Schn., 1866.
Males 0·8 to 1·05mm. in length; females, 0·9 to 1·3mm. in length. The posterior extremity of the body of the male has a heart-shaped bursa, and seven to ten ribs on each side; the bursa may, however, be lacking. The spicules measure 0·027 to 0·033mm. in length, but are never quite alike. The posterior extremity of the female is long and pointed; the vulva lies somewhat behind the middle of the body, the ovary is single, the eggs are oval, 60µ by 35µ.
This species was found in Stuhlweissenburg by Scheiber in the acid urine (containing albumin, pus and blood) of a woman suffering from pyelonephritis, pneumonia and acute intestinal catarrh; the observer was able to convince himself that the Nematodes which were found during the whole period of the illness lived in the vagina, and were evacuated with the urine.
Oerley proved that this species had long been known; during its larval stage (Anguillula mucronata, Grube, 1849) it lives in earthworms; in its adult stage it lives in decomposing matter in the soil. By introducing individuals of this species into the vagina of mice, Oerley succeeded in obtaining infection and multiplication (facultative parasitism). These Nematodes must in some such way have got into the vagina of Scheiber’s patient.
Two other cases described by Baginsky and Peiper probably belonged to the same or a nearly related species.
Rhabditis niellyi, Blanchard, 1885.
Syn.: Leptodera niellyi, Blanchard, 1885.
In 1882 Nielly had a cabin-boy, aged 14, under observation in Brest. The lad had never left the neighbourhood of Brest, and had suffered from itching papules on the skin for five or six weeks; in the papules the observer found one or several rhabdites, measuring 0·33mm. in length by 0·30mm. in breadth. Their cuticle presented a delicate transverse striation; the intestine was the only internal organ recognizable, and it opened somewhat in front of the posterior extremity. Therefore, it must have belonged to the rhabditis-like larva of a Nematode, the adult stage of which is unknown.
The manner of infection was established almost certainly by a further observation of Nielly’s: at the commencement of the illness small Nematodes were found in the blood of the patient; later on, however, they disappeared, neither were Nematodes found in the fÆces, urine or sputum. Therefore it must be concluded that the cabin-boy, who was in the habit of drinking water from brooks, had thus ingested embryo-containing eggs of a Nematode; the young hatched out in the intestine, perforated it, reached the blood and then settled in the skin; but, on the other hand, the entry may have been direct through the skin.
In connection with the foregoing, reference should be made to a communication by Whittles, insufficient from a zoological point of view. In a case of hypertrophic gingivitis occurring in a female patient, aged 19, who had never left Birmingham, he found Nematode larvÆ in the periosteum of the upper jaw, which was excised after extraction of the right premolar; the genital rudiment could be recognized in them. Similar larvÆ were found in the same patient in abscesses in various regions of the skin, and in the case of her mother in the blood. The author considers that the infection took place through a dog, and refers to the case of O’Neil (1875), who found FilariÆ in the skin (in the condition known as “craw-craw”), referred by Manson to Filaria perstans. O’Neil’s case was quoted, and attributed to Filaria sanguinis hominis. In conclusion, the author states that he has repeatedly found Nematode larvÆ in the blood of persons who suffered from pruritus; in his opinion the parasite had been imported through the agency of troops returned from South Africa. Glatzel found true Filaria larvÆ in a pustule of a cutaneous eruption of the trunk and extremities in a patient at Dar-es-Salam.
Skin diseases which are caused by young Nematodes are also observed in dogs (Siedamgrotzky, MÖller, J.G. Schneider, KÜnnemann), foxes (Leuckart), and horses (Semmer). ZÜrn found young Nematodes (AnguillulidÆ) also in pig’s flesh. In KÜnnemann’s case it was shown that the adult Rhabdites lived in the straw upon which the dog lay.
Rhabditis, sp.
In the fluid obtained by lavage from the stomach of a female patient, aged 16, suffering from ozÆna, O. Frese found during two consecutive months Rhabdites of various ages, 0·275 to 0·64mm. in length, the adults all with eggs; males were not found; transmission into rabbit’s stomach failed, but they could be kept alive in
Genus. Anguillula, Ehrenberg, 1826.
Buccal cavity very small, without lips. Males without bursa, but with a series of papillÆ. Lateral lines absent.
Anguillula aceti, MÜller, 1783.
Cuticle unstriped, body cylindrical, anterior end tapering but little, posterior end long, pointed. Male up to 1·45mm. long, 0·024 to 0·028mm. wide; two pre-anal papillÆ, one post-anal; spicules equal, curved, 0·038mm. long; gubernaculum present; testis extending in front of mid-line of body. Female up to 2·4mm. long, 0·040 to 0·072mm. wide; anterior uterus reaching to near the oesophagus, posterior to hind gut. Viviparous; embryos in both or only in one uterine horn, 0·22mm. long, 0·012mm. broad.
The species is a frequent inhabitant of vinegar (prepared by older methods), and was once observed for some time by Stiles and Frankland in the urine of a woman; the urine had an acid reaction, and once had a distinct odour of vinegar. It was assumed that the patient, who was hysterical and suffered from chronic nephritis, employed vaginal douches with diluted vinegar, perhaps to deceive her physician or to protect herself against conception. According to Ward, Billings and Miller are said to have reported on two other cases. Ill-effects which might be connected with the vinegar eel (Anguillula aceti) were not present.
Genus. Anguillulina, Gervais and Beneden, 1859.
Syn.: Tylenchus, Bastian, 1864.
Characterized by the possession in the buccal cavity of a spine knobbed posteriorly; bursa present; uterus asymmetrical. Numerous species parasitic in plants.
Anguillulina putrefaciens, KÜhn, 1879.
Syn.: Tylenchus putrefaciens, KÜhn; Trichina contorta, Botkin, 1883.
In 1883 Botkin (Pet. klin. Wochenschr., 1883) found a small Nematode, which was, however, entirely mistaken, in the material vomited by a Russian; this was not a species of Trichinella, but an Anguillulina living in onions which had already, in 1879, been described by KÜhn as Tylenchus putrefaciens; the Nematodes got into the stomach with the onions, causing nausea and vomiting.
Family. AngiostomidÆ, Braun, 1895.
Fig. 270.—Strongyloides stercoralis, female: parasitic generation from gut of man. ×70. (After Looss.)
Genus. Strongyloides, Grassi, 1879.
Syn.: Pseudorhabditis, Perroncito, 1881; Rhabdonema, Leuckart, 1882, p.p.
The genus is insufficiently defined. The parasitic form possesses a simple mouth opening directly into the long cylindrical oesophagus which occupies the anterior third of the body. The free-living forms possess a small buccal cavity; the oesophagus is short, with a double bulb, in the hinder one there is a Y-shaped chitinous valve; two spicules of equal size.
Strongyloides stercoralis, Bavay, 1877.
Syn.: Anguillula intestinalis et stercoralis, Bavay, 1877; Leptodera intestinalis et stercoralis, Cobb.; Pseudorhabditis stercoralis, Perroncito, 1881; Rhabdonema strongyloides, Leuckart, 1883; Strongyloides intestinalis, Grassi, 1883; Rhabdonema intestinale, Blanchard, 1886.
In 1876, a number of French soldiers returned to Toulon from Cochin China suffering from severe diarrhoea. Dr. Normand, under whose treatment they were, discovered a large number of Nematodes in the evacuated fÆces, and Bavay described them as Anguillula stercoralis. Soon after Normand, at the post-mortem of five patients who had died of Cochin China diarrhoea, found numerous other Nematodes in the intestine, from the stomach to the rectum, in the bile-ducts and in the pancreas, and these he handed over to Bavay. The latter diagnosed another
Fig. 271.—Strongyloides stercoralis, male: free-living generation. ×170. (After Looss.)
(1) The parasitic generation (strongyloid or filariform ?) is quite colourless and cannot be seen in situ even with a lens. To detect them it is necessary to scrape the mucosa of the jejunum and examine the scrapings microscopically. It measures 2·2mm. in length, and 34µ to 70µ in breadth; the cuticle is finely transversely striated; the mouth is surrounded by four lips; the oesophagus is almost cylindrical and a third the length of the entire body. The anus opens shortly in front of the pointed posterior extremity; the vulva is situated at junction of middle and posterior thirds of the body; the uterus has no special ovejector; the eggs measure 50µ to 58µ in length, and 30µ to 34µ in breadth, and lie in a chain one behind the other (fig.270). As in the case of Angiostomum nigrovenosum, Leuckart considers this stage to be hermaphroditic, the testes degenerating after having functioned; other authors (Rovelli) regard it as a female reproducing by parthenogenesis.
(2) The free-living generation (? and ?) has a smooth body, cylindrical, somewhat more slender at the anterior extremity and pointed at the tail end. The mouth has four indistinct lips; the oesophagus is short with a double (rhabditis-like) bulb; there is a Y-shaped valve in the posterior bulb; the anus opens in front of the tail end. The males measure 0·7mm. in length, 0·035mm. in breadth. Their posterior end is rolled up; the two brown spicules are small (38µ) and much curved. There is also a gubernaculum. The females measure 1mm. in length or a little over; 0·05mm. in breadth. The tail end is straight and pointed; the vulva lies somewhat behind the middle of the body. The yellowish, thin-shelled ova measure 70µ in length and 45µ in breadth.
Fig. 272.—Strongyloides stercoralis, female; free-living generation, ×170. (After Looss.)
As Askanazy has shown, the parasitic form bores deeply into the mucous membrane of the intestine, and frequently into the epithelium of LieberkÜhn’s glands, both for nourishment and oviposition. The eggs then develop in the intestinal wall. The eggs which are found in scrapings from the mucosa occur, at least in the case of Strongyloides of the sheep, in chains enclosed in a thin tube or sheath, the origin of which is doubtful; possibly it is the uterus. The eggs themselves are only rarely found in stools, e.g., after a strong purge. The larvÆ, which are hatched out, and measure 0·2 to 0·25mm. long by
Fig. 273.—Strongyloides stercoralis: larva from fresh human fÆces. ×310. (After Looss.)
The females of the free-living generation (rhabditiform) deposit from thirty to forty eggs, which develop rapidly, sometimes even within the uterus in the case of old females. After the larvÆ have emerged from the egg-shell, they measure 0·22mm. in length, and possess the characteristics of the parents (rhabditiform larvÆ). When they have grown to 0·55mm. they moult, and while losing their own characteristics they acquire the characteristics of their parasitic grandparents (strongyloid or filariform). After about eight days the free-living adult generation in the cultures have disappeared, and all the rhabditiform larvÆ have been transformed into strongyloid or filariform larvÆ; they then die off unless they reach the intestine.
Fig. 274.—Strongyloides stercoralis: mature filariform larva showing long transparent oesophagus, slender granular intestine and characteristic tip to the tail ending in two small points. ×620. (After Looss).
This cycle of development holds good for Strongyloides stercoralis of tropical origin (Bavay, Leuckart, Leichtenstern, Zinn). In the European Strongyloides the free-living generation, as a rule, is absent (Grassi, Sonsino, Leichtenstern, Braun); the rhabditis-like larvÆ evacuated with the fÆces are transformed into the strongyloid or filariform type of larva (in cultures which are easily made) which will only become adult if introduced into man.
So that we have these two cycles: (A) (1) ? parasitic, (2) eggs, the rhabditiform larvÆ in fÆces, (3) free-living strongyloid or filariform larva, (4) ? parasitic. (B) (1) (2) (3) as before, then (4) adult ? and ?, free living, (5) eggs, (6) rhabditiform larva, (7) strongyloid or filariform larva, (8) ? parasitic.
Infection of man results not only
Occurrence in Man.—As already mentioned, Strongyloides stercoralis was first observed in persons suffering from so-called Cochin China diarrhoea. From the enormous numbers of parasites evacuated with the fÆces, the cause of the disease was apparently evident. It appeared, however, that only some of the soldiers returning from Cochin China and Martinique, and suffering from diarrhoea, harboured Strongyloides (Chauvin). Breton made the same observations in Cochin China and found that only 10·4 per cent. of cases of chronic dysentery, and 8·8 per cent. of chronic diarrhoea, show Strongyloides. Normand, moreover, found that only a few of the Europeans residing in Cochin China are exempt from S. intestinalis, yet the people exhibit no intestinal symptoms; if, however, from any cause a catarrhal condition of the intestine supervenes the condition is changed, the parasites appear in larger numbers, and the disorder is considerably intensified.
S. intestinalis, besides being present in the Indo-China region, also occurs in the Antilles, in Brazil, Africa, and Europe; in 1878 it was discovered in Italy by Grassi and C. and E. Parona; in 1880 it was also found in the labourers working at the St. Gothard tunnel. It was imported into Germany, Belgium, and the Netherlands by Italian labourers. One sporadic case has been observed in East Prussia, and the worm has also been reported from Siberia.
In mammals the following species are found: Probstmayria (Strongyloides) vivipara, Ransom, 1907, in Equus caballus; Strongyloides fÜlleborni, v. Linst., in Anthropopithecus troglodytes and Cynocephalus babuin.
Their development is, so far as is known, the same as that of Strongyloides stercoralis (v. Linstow, Centralbl. f. Bakt., Path. u. Infektionsk., 1905, Orig. xxxviii, p. 532).
Family. GnathostomidÆ.
Genus. Gnathostoma, Owen, 1836.
Syn.: Cheiracanthus, Diesing, 1839.
Easily recognizable by the numerous spines which cover the entire body or only the anterior extremity, and terminate in several points; head globular and beset with bristles; mouth with two lips; two spicules; vulva situated behind the middle of the body.
Gnathostoma siamense, Levinsen, 1889.
Syn.: Cheiracanthus siamense, Lev., 1889.
Fig. 275.—Gnathostoma siamense: to the left, the entire worm (8/1); to the right the head seen from above, with two fleshy lips (about 40/1). (After Levinsen.)
Female measures 9mm. in length, 1mm. in breadth. There are eight rows of simple spines on the head; the armature of spines extends over the anterior third of the body only; each spine on the anterior region of the body spreads into three points, of which the middle one is the longest; the posterior spines are simple; they gradually become smaller and then disappear entirely. The vulva is situated behind the middle of the body.
Male.—10·5mm. long by 0·6mm. broad. Head terminates in a
Spicules 1·1 and 0·4mm. respectively.
Leiper considers Gnathostoma siamense to be identical with Gnathostoma spinigerum.
The single specimen described by Levinsen was found by Deuntzer in Bangkok (Siam), and was obtained from a young Siamese woman who suffered from a small tumour of the breast which had developed in the course of a few days. After the disappearance of the tumour, nodules the size of beans were found in the skin; out of one of these the worm was obtained. The same observer saw this affection in two other persons.
A closely related species, Gnathostoma spinigerum, Ow., lives in the stomach of wild cat (Felis catus), puma (Felis concolor), tiger (Felis tigris), and domestic cat (India); another species, Gnathostoma hispidum, Fedsch., 1839, in the stomach of pigs in Turkestan, Annam, Hungary, Congo, and by Collin in the stomach of an ox (Berlin).
Gnathostoma sp. in pariah dogs, Calcutta. Gnathostoma sp. in monkeys, French Guiana. They produce large fibrous thickenings in the stomach wall.
Gnathostoma spinigerum, Owen, 1836.
Cuticle of bulb with eight rows of chitinous laminÆ with their posterior edges notched into spines. The laminÆ on the anterior portion of the body are similar trident laminÆ. In the middle of the body, the laminÆ are simple and conical, cuticle posteriorly is unarmed. Mouth with two fleshy lips.
Male 5mm. long by 0·5mm. broad; tail spiral, four pairs of papillÆ.
Female about twice as long; tail straight, trilobed.
Family. DracunculidÆ, Leiper, 1912.
Genus. Dracunculus, Kniphoff, 1759.
Anterior end rounded with a cuticular thickening or shield. Mouth triangular with two lips. Alimentary canal atrophied.
Dracunculus medinensis, Velsch, 1674.
Syn.: Vena medinensis, Velsch, 1674; Dracunculus persarum, KÄmpfer, 1694; Gordius medinensis, LinnÉ, 1758; Filaria dracunculus, Bremser, 1819; Filaria Æthiopica, Valenciennes, 1856; Dracunculus medinensis, Cobbold, 1864; Guinea worm, Medina worm.
Fig. 276.—Guinea worm (Dracunculus medinensis). (After Leuckart.)
The females attain a length of 50 to 80cm., or even more, and average 1·5 to 1·7mm. in diameter. They are whitish or yellowish in colour. The anterior extremity is roundish and bears a cuticular thickening or shield. The triangular mouth opening is surrounded by two projections or lips, behind which on the shield there are two lateral and four sub-median papillÆ; the posterior end terminates in a spine, ventrally directed, and about 1mm. in length; the alimentary canal below the oesophagus is atrophied, but not entirely obliterated; anus absent; the lateral lines are very flat. The greater part of the body is occupied by the long uterus, in which a great number of young larvÆ are always found. The ovaries probably lie at the ends of the uterus; the vulva lies just behind the cephalic shield. During parturition the uterus is prolapsed through this opening.
Fig. 277.—Anterior extremity of Guinea worm, showing dorsal and ventral lips, one lateral and two submedian papillÆ and the lateral line. (After Leuckart.)
The male is almost unknown. Leiper in an experimentally infected monkey found two males 22mm. long, one from the psoas muscle, the other from the connective tissue behind the oesophagus.
Occurrence.—Filaria medinensis has been known since the most remote period. The “fiery serpents” that molested the Israelites by the Red Sea, and which Moses mentioned, were probably filariÆ. The term ??a???t??? occurs in Agatharchides (140 B.C.). Galen called the disorder dracontiasis; the Arabian authors were well acquainted with the worm. It is found not only in Medina or Arabia, but also in Persia, Turkestan, Hindustan. The Guinea worm is also widely distributed in Africa, on the coasts as well as in the interior. It occurs in the Fiji Islands. It was carried to South America by negro slaves, but is said at the present time to exist in only quite a few places (British Guiana, Brazil [Bahia]); it is also observed in mammals (ox, horse, dog, leopard, jackal [Canis lapuster], etc.).
Fig. 278.—Dracunculus medinensis. a, anterior extremity seen end on; O, mouth; P, papillÆ; b, female reduced more than half; c, larvÆ enlarged. (After Claus.)
Dracunculus medinensis in its adult stage lives in superficial ulcers on the body surface; it is seen most frequently on the lower extremities, more especially in the region of the ankle, but it also occurs in other parts of the body—on the trunk, scrotum, perineum, on the upper extremities, and in the eyelids and tongue. Sometimes there is only one ulcer and one worm, but more commonly several. It attacks man without distinction of race, age or sex. It is observed most frequently during the months of June to August.
Life history.300—When about a year old the worm seeks the surface
The larvÆ are 500µ to 750µ by 15µ to 25µ, with a long slender tail about one-third of the total length. The cuticle is transversely striated. The body is flattened. They possess an oesophagus and gut. At the anus there are apparently glandular structures.
The larvÆ live and move actively in water for about two days, the majority dying on the third (Leiper). If a number of Cyclops sp. have been collected and isolated in clean water, and the larvÆ are now added, the further development can be traced.
Fig. 279.—Transverse section of female Guinea worm; u., uterus containing embryos; i., intestinal canal; o., ovary. (After Leuckart.)
The larvÆ enter the Cyclops, according to most authorities, by penetrating the exoskeleton, but according to Leiper this is impossible; they must enter by the mouth and penetrate the gut in order to reach the body cavity. In eight days moult 1 takes place, the striated cuticle being cast off. In ten days moult 2 takes place. In five weeks the larva is mature. If now the infected Cyclops is placed in 0·2 per cent. HCl solution the Cyclops is killed immediately, but the larvÆ are stirred into activity, escape from the body, and swim about in the acid. This suggests that infection in nature probably takes place by the swallowing of infected Cyclops; Leiper, by feeding Cyclops containing mature larvÆ to a monkey, found in it, post mortem six months later, two immature females 30cm. long and two males 22mm. long.
In certain areas the new cases occur principally in June. Five
Pathology.—The initial induration is accompanied by itching. Urticarial eruptions are described in Dahomey and Mauretania accompanied by fever, rigors, blood-shot conjunctiva, and prostration resembling fungus poisoning. Symptoms last for one to two days, later the worms appear on the surface.
Fig. 280.—Cyclops virescens, ?. 8, Female, ventral view, ×120; 9, anterior antennÆ ×240; 10, urosome and last thoracic segment, ×240; 11, foot of first pair, ×320; 12, 15, 16, foot of second, third and fourth pairs, ×240; 14, foot of fifth pair, ×440; 13, last thoracic segment and first segment of urosome of male, ×240.
If the worm is ruptured in an attempt to extract it, disastrous results may occur through the escape of the larvÆ into the tissues: fever, inflammation, abscess, sloughing, ankylosis, even death from sepsis. Eosinophilia is often marked, 11 to 13 or even 50 per cent.
Extraction.—(1) The native method consists in rolling the worm round a stick; 1in. to 2in. are extracted each day, the process taking about a fortnight; (2) Emily used injections of 1 in 1,000 sublimate into the swelling or into the worm itself fixed by a ligature.
CyclopidÆ.—Cephalothorax ovate, clearly separated from abdomen. Anterior antennÆ of female when bent back scarcely ever stretch beyond the cephalothorax. The second antennÆ are unbranched. First four pairs of feet two-branched, outer branches three-jointed. The fifth pair of limbs are rudimentary alike in both sexes, usually one-jointed. There is no heart. The female has two egg sacs containing about fifty eggs.
Genus. Cyclops, MÜller, 1776.
Mandible palp rudimentary, reduced to a tubercle bearing two branchial filaments. Maxillary palp rudimentary (obsolete). Lower foot-jaw non-prehensile. Head ankylosed to first thoracic segment.
Family. FilariidÆ.
Sub-family. FilariinÆ.
The residue after exclusion of the ArduenninÆ and OnchocercinÆ.
Genus. Filaria, O. Fr. MÜller, 1787.
Very long, slender Nematodes, without excretory vessels or excretory pore, the males of which are usually considerably smaller than the females. Mouth round, without lips, unarmed. The lateral lines occupy one-sixth of the circumference of body. The tails of the males are bent or spirally rolled, and bear little wing-like appendages. The two spicules are unequal; almost always there are four pre-anal papillÆ, but the number of post-anal papillÆ varies. The vulva is always situated at the anterior extremity. Parasitic chiefly in the serous cavities and in the subcutaneous connective tissue. Insufficiently defined.
Filaria bancrofti, Cobbold, 1877.
Syn.: Trichina cystica, Salisbury,301 1868 (nec Filaria cystica, Rud., 1819); Filaria sanguinis hominis, Lewis, 1872; Filaria sanguinis hominis Ægyptiaca, Sonsino, 1875; Filaria wÜchereri, da Silva Lima; Filaria sanguinis hominum, Hall, 1885; Filaria sanguinis hominis nocturna, Manson, 1891; Filaria nocturna, Manson, 1891.
These parasites of man were for a long time only known in their larval stage. They were discovered in 1863 in Paris by Demarquay, in the hydrocele fluid of a Havanese emptied by puncture; they were next observed by WÜcherer, in Bahia, in the urine of twenty-eight cases of tropical chyluria; they were likewise observed in North America by Salisbury, who gave them the name of Trichina cystica. The next discoveries (in Calcutta, Guadeloupe, and Port Natal) related to chyluria patients, until Lewis discovered the larvÆ in the blood of man (India), and
Fig. 281.—Filaria bancrofti. 1, Anterior portion of male; 2, two rows of papillÆ on head; 3, papillÆ of tail of male; 4, cloaca of male showing tips of spicules and gubernaculum; 5, the spicules and gubernaculum of male. (After Leiper.)
Head bougie-like, i.e., separated by a narrowing from the neck, having two rows of minute papillÆ. Cuticle has extremely fine striations.
Female.—50 to 65mm. long by 1·5 to 2mm. broad. Vulva 0·4 to 0·7mm. behind the head. Anus about 14mm. from the tip of the tail (vulva 1 to 1·3mm. from head, and anus 0·17 to 28mm. from tail according to other authors). The vagina is a muscular tube forming three bold loops, and has terminally a pyriform enlargement. Uterus double (or single). Ovoviviparous.
Male.—25 to 30mm. long by 0·1mm. thick (40 by 0·1mm. according to various authors). Probably two pairs of pre-anal papillÆ, eight pairs of peri-anal, two pairs of post-anal papillÆ, and one pair terminal. Tail curved. Two spicules, 0·2 and 0·6mm. respectively, and a cup-like gubernaculum. The long spicule is cylindrical, expanded proximally and tapering distally to a filament with wings. At the tip it is spoon-like. The short spicule is of the same diameter throughout. It is gutter-like, coarsely marked. Testis uncoiled, terminating in a snowdrop-like process (Leiper).
Eggs.—40µ by 25µ. They do not appear to possess a true shell, but only an embryonal or vitelline membrane secreted by the ovum.
Embryos.—In the posterior part of the uterus eggs occur, in the anterior part embryos; the larvÆ at birth measure 127µ to 200µ by 8µ to 10µ. In the blood they measure in the fresh 260µ by 7·5µ to 8µ. In stained films, owing to shrinkage, there is great variation in size, from 154µ to 311µ. Probably 260µ to 285µ is the average in stained films.
Geographical Distribution.—Europe: Two cases recorded, one from near Barcelona. The patient suffered from hÆmato-chyluria and enlarged scrotum with mikrofilariÆ in the blood. A second case from Siena. Africa: The filarial index has not been estimated for various parts. In Nigeria it is about 10 per cent.
Habitat.—Lymphatic glands: e.g., inguinal, femoral, iliac, lumbar, mesenteric, bronchial, superficial cervical, epitrochlear.
Lymphatic vessels: e.g., those draining into the receptaculum chyli of the spermatic cord, in the thoracic duct and in various different parts.
Organs, etc.: Testis, epididymis, spermatic cord, tunica vaginalis, mammary cyst, and in abscesses.
They may occur in masses, but usually only a few (one to eight). Females are commoner than males. Dead and calcified worms are common in the various sites.
Distribution of LarvÆ in Body.—These are by no means uniformly distributed, but occur in greater number in the capillaries of the lungs. Besides the lungs they occur in the capillaries of other organs, as the following data of Rodenwaldt show:—
| MikrofilariÆ | MikrofilariÆ | ||||
| Lungs | 134,821† | Spleen | 1,666 | ||
| Liver | 4,884 | Brain | 3,833 | ||
| Kidneys | 15,253 | Glands | 0 | ||
| Glomeruli | 8,008 | Marrow | 0 | ||
| Parenchyma | 7,245 | Blood | 3,000 | ||
† These figures refer to 1c.c. of each organ, and were estimated by cutting sections of definite thickness (30µ to 40µ) and counting the filariÆ in a definite area of section, e.g., 14cm.2 The organs before removal from the body have their vessels tied, and are then fixed in hot alcohol.
The following data of Rodenwaldt refer to the larvÆ of Filaria immitis in the dog. They are commoner in organs than in vessels, and especially in the capillaries of the organs, but in the lungs they appear to be equally distributed in capillaries, arteries and veins.
The length of life of larvÆ is unknown, but they appear to be destroyed in the kidneys, as dead calcified specimens are fairly numerous in the capillaries of the vasa recta of the medullary substance.
Kidneys: mainly in the glomerular capillaries and those of the vasa recta.
Liver: in the capillaries of the portal system, especially in those between the interlobular and the central intralobular veins.
Periodicity of LarvÆ.302—Roughly speaking, the larvÆ of Filaria bancrofti are found in the peripheral blood only during the night, disappearing (but not entirely) during the daytime. Their periodicity and that of Loa loa larvÆ is shown by the table on p.394, based on that of Smith and Rivas (Amer. Journ. Trop. Dis. and Prev. Med., 1914, vol.iii, p.361).
It was discovered by Mackenzie that this periodicity could be reversed by making the patient sleep during the daytime, showing that the phenomenon was in some way dependent on sleep or its attendant phenomena. Rodenwaldt gives the following explanation of the phenomenon of periodicity:—
MikrofilariÆ come to rest in capillaries. After passing up the thoracic duct they would reach the capillaries of the lungs by the superior vena cava. Here they occur in immense numbers. In the case of Loa loa larvÆ (which have a diurnal periodicity) some of these are forced out by the increased force and rapidity of the pulmonary circulation during the day, but are able to rest (owing to their sticky sheath?) in the peripheral capillaries on their way to the capillaries of the organs. During the night the force of the current through the lungs is relaxed and consequently they are able
| LarvÆ of L. loa in equal quantities of blood | Average 132. Deviations from average | Case 1. F. bancrofti larvÆ in 1c.c. of blood | Average 1,000 (about). Deviations from average | Case 2. F. bancrofti larvÆ in 1c.c. of blood | Average 1,570 (about). Deviations from average | ||
| 2 | a.m. | 9 | – 123 | 3,500 | + 2,500 | 6,500 | + 3,930 |
| 4 | a.m. | 11 | – 121 | 3,200 | + 2,200 | 5,200 | + 3,630 |
| 6 | a.m. | 41 | – 91 | 2,800 | + 1,800 | 2,000 | + 430 |
| 8 | a.m. | 168 | + 36 | 900 | – 100 | 1,100 | – 470 |
| 10 | a.m. | 298 | + 166 | 210 | – 790 | 350 | – 1,220 |
| 12 | noon | 531 | + 389 | 30 | – 970 | 50 | – 1,520 |
| 2 | p.m. | 252 | + 120 | 20 | – 980 | 40 | – 1,530 |
| 4 | p.m. | 146 | + 14 | 10 | – 990 | 30 | – 1,540 |
| 6 | p.m. | 91 | – 41 | 40 | – 960 | 40 | – 1,530 |
| 8 | p.m. | 23 | – 99 | 60 | – 940 | 100 | – 1,470 |
| 10 | p.m. | 5 | – 127 | 600 | – 400 | 800 | – 770 |
| 12 | midnight | 5 | – 127 | 750 | – 250 | 2,600 | + 1,030 |
| Total | 1,580 | — | 12,120 | — | 18,810 | — | |
In certain countries, e.g., Fiji, Samoa, Philippines, West Africa, larvÆ, apparently those of Filaria bancrofti, show no periodicity. In Fiji the usual intermediate host is Stegomyia pseudoscutellaris, a day-biting mosquito, so that possibly, as Bahr suggests, the mikrofilariÆ have partly adapted themselves to the habits of their intermediate host, as the nocturnal mikrofilariÆ are adapted for transmission by a nocturnal feeding mosquito, e.g., Culex fatigans, but how this could come about is a mystery. It is not certain in all cases whether the non-periodic mikrofilariÆ really belong to Filaria bancrofti; some may be L. loa larvÆ, or possibly unknown larvÆ. An exact morphological description of these larvÆ is therefore always necessary.
Preservation of Living LarvÆ.—Blood from the vein (or finger puncture) is shaken up with twenty times its volume of sterile 0·9 per cent. salt solution, and kept in an ice cupboard (FÜlleborn).
Concentration of LarvÆ.—(a) The above mixture is hÆmolysed with water and then sufficient salt solution added to make up to 0·9 per cent. The solution is allowed to stand or can be centrifugalized. (b) The blood is mixed with sodium citrate and centrifugalized; the larvÆ are found in the leucocytic layer (Bahr). (c) Allow blood to clot in a small tube; the larvÆ appear on the surface of the clot and are so got in pure serum. A drop of blood may also be allowed to clot on the slide; the larvÆ are found in the clear areas of serum. (d) HÆmolyse blood with water or acetic acid. Centrifugalize, make smears from, or examine the sediment.
Removal of Red Corpuscles.—The blood film is allowed to stand for some minutes in a moist atmosphere. The staining solution is sucked through with blotting paper: the larvÆ stick to the slide, while the corpuscles are washed out.
Morphology of LarvÆ.—Wet staining: Azur II one part, 0·9 per cent., salt solution 3,000, or very dilute Giemsa or ripened methylene blue or neutral red solutions. Place a drop on the slide and add a drop of blood to this. The larvÆ remain alive for one or more days; it sometimes takes twenty-four hours to stain some particular structure. Differentiation by drawing through weak eosin solution is often useful. This method is the best for finest details. The excretory pore, anal pore, excretory cell, and chief “genital” cell stain first, then the matrix cells and finally the column of nuclei.
Wet fixation and staining: The blood is spread on a large cover-glass—floated on the surface of 70 per cent. alcohol heated to about 70°C. Wash in water, (1) overstain with 1 in 1,000 azur II solution, warming slightly; (2) differentiate with (a) absolute alcohol (containing, if necessary, a trace of HCl), or (b) with absolute alcohol 96 per cent. ninety parts, anilin oil ten parts; (3) clear in origanum, bergamot or cajeput oil; (4) mount in balsam. Or stain with hÆmatoxylin, e.g., Mayer’s glycerine alumhÆmatein, heating till slightly steaming. Differentiate with acid (2 per cent. HCl) alcohol if overstained. Clear and mount as above.
Dry fixation and staining: (1) With azur II as above, or (2) with hÆmatein (warm). Examine the dried films in the usual way without a cover-glass. The azur stains the excretory and genital cells clearly.
Thick films: (1) The blood is smeared out fairly thickly over an area as big as a sixpence.
(2) Dry quickly to prevent shrinking, using carefully a spirit lamp in a moist climate.
(3) Place films downwards in water for a few minutes.
(4) Fix in alcohol.
(5) Stain with azur II, 1 in 1,000. Differentiate as above. Examine as a dry film. This method suffices for showing the excretory cell and the G1 cell; or
(6) Stain with hÆmatein (slightly steaming), especially for the column of nuclei and the sheath. The fixation in alcohol in this case may be omitted.
(7) The removal of the hÆmoglobin and the fixation may be combined by using Ruge’s mixture (formalin 2 per cent., containing 1 per cent. acetic acid) or acetic alcohol (glacial acetic 1, alcohol 3).303
Structure of LarvÆ.—(1) Subcuticular cells: By vital staining, at intervals underneath the cuticle are seen a series of spindle-shaped cells—the subcuticular matrix cells of Rodenwaldt, the muscle cells of FÜlleborn. There are thirty or forty or more of these.
(2) Nerve ring: Appears as a break in the nuclear column about 20 per cent. of total length from the head.
(3) Excretory system: Consists of a lateral spherical hollow excretory pore which shows a radial striation. Connected with the pore is an excretory cell which appears to be canalized. Excretory pore, 29·6 per cent. of length from head. Excretory cell, 30·6 per cent. of length from head.
(4) “Genital” cells and anal pore: Consists of a pore opening ventrally on a very fine papilla with which are connected four other cells in series, the chief “genital” cell (G1) being some distance from the three others, which lie close to the pore. G1, 70·6 per cent., anal pore, 82·4 per cent. of length from head.
(5) Internal body, viscus, or reserve material: Best shown by vital staining with neutral red. This is a granular strand-like body extending from 52·7 per cent. to 65 per cent. of length from head.
(6) Tail end: (i) Rod-like structures resembling those in the head, 90 per cent. of length. (ii) The column of nuclei extends to 95 per cent. of length, so that the terminal portion is free from nuclei.
(7) Mouth: Terminal according to some authors, lateral according to others. Some describe a fang on the head, others not. By vital staining and eosin differentiation two rod-like structures with mushroom-like caps can be seen behind the head.
(8) Cuticle: Transversely striated. There is a longitudinal break in the striation on each side corresponding to the lateral lines. The striation is best shown by vital staining with azur II and eosin differentiation.
(9) Column of nuclei: These nuclei of the gut cells form the main feature in ordinary dry films stained with hÆmatoxylin. They are separated by a space from the subcuticular cells.
Fig. 282.—Mf. bancrofti in thick film, dried and stained with hÆmatoxylin: 1, shrunken; 2, unshrunken. ×1,000. (After FÜlleborn)
Distinction between Mikrofilaria bancrofti AND Mikroloa loa.
| Dry Films, HÆmatoxylin Staining:— | ||
| Mf. bancrofti. | Ml. loa. | |
| (1) In graceful curves (but only if quickly dried). | (1) Kinked. | |
| (2) Tip of tail free from nuclei. | (2) Nuclei extend to tip. | |
| (3) Column of nuclei separated by a space from the cuticle. | (3) Not so distinctly. | |
| Azur Staining:— | ||
| (4) G1 cell small, easily overlooked. | (4) G1 cell large, stains deep blue, cell protoplasm = twice width of larva, easily seen. | |
| (5) Excretory cell close to excretory pore, 2per cent. of length. | (5) Excretory cell farther from pore, 4per cent. of length. | |
| Vital Staining with Neutral Red:— | ||
| (6) Internal body or reserve material clearly shown. | (6) Not shown. | |
Life History.—In the stomach of the mosquito the larvÆ cast their sheath in the thickened blood in one to two hours. In twenty-four hours the majority have reached the thoracic muscles, where development proceeds. They are at first immobile and of a “sausage” form (110µ by 13µ), with a short spiky tail. In three to five days the oesophagus is formed, the larva now being 0·5mm. long. The larva appears to moult at this time. After the gut is formed papillÆ, three or four in number, appear at the tail end. In two to three weeks the larvÆ are 1·5mm. long. They now leave the thorax and reach the labium, but they may be found in various parts of the body, e.g., the legs. They bore through Dutton’s membrane and so arrive on the surface of the skin, which they rapidly enter. Their development in man is unknown, but it may be very long, as children are not infected till 4 to 5, or even 10 years old, but this may be due to unknown causes.
Development takes place in numerous mosquitoes. Anophelines: Myzomyia rossii, Pyretophorus costalis, Myzorhynchus sinensis, Myzorhynchus barbirostris, Myzorhynchus peditÆniatus.
Culicines: Culex pipiens, Culex fatigans, Culex skusei, Culex gelidus, Culex sitiens, Culex albopictus, Stegomyia fasciata, Stegomyia pseudoscutellaris, Stegomyia gracilis, Stegomyia perplexa, Mansonioides uniformis, Mansonioides annulipes, Scutomyia albolineata, TÆniorhynchus domesticus.
Partial development takes place in other species.
Fig. 283.—Schematic drawings of the anatomy of Ml. loa and Mf. bancrofti combined from specimens stained in different ways. The position of the organs has not been based on the average values of a large series of specimens, but on that of a single specimen. G1, chief genital cell; G2–4, other genital cells; Ex.-C., excretory cell; Ex.-P., excretory pore; A-P., anal pore; N., nerve ring. Magnification circa 1,000. (After FÜlleborn).
Pathology.—Among the conditions which Filaria bancrofti is
(1) The prevalence of filarial diseases is proportional to the prevalence of Mikrofilaria bancrofti in the blood. Thus in four villages examined by him he got the following figures:—
| Village A | Village B | Village C | Village D | ||||||
| Mf. bancrofti | 12 | ·5 | per cent. | 25 | per cent. | 31 | per cent. | 33 | per cent. |
| Filarial diseases | 29 | " | 39 | " | 58 | " | 34 | " | |
| Total population | 168 | 114 | 425 | 222 | |||||
(2) Out of 257 people with Mf. bancrofti in the blood, 153 were suffering from filarial diseases, i.e., 59 per cent.
(3) Whereas of 672 people without Mf. bancrofti in the blood, only 263 were suffering from filarial diseases, i.e., 37·6 per cent.
(4) Again out of 416 people suffering from filarial disease, 153 showed Mf. bancrofti in their blood, i.e., 36·7 per cent.
It is generally assumed that all people suffering from filarial disease show at some (presumably early) stage larvÆ in the blood; but we do not consider that this must necessarily be so. It appears to us quite possible that living adult filariÆ may be present in the body, producing disease, without their larvÆ appearing in the blood. The absence of larvÆ from the blood in 63·3 per cent. of persons suffering from filarial disease is, however, generally explained otherwise. The adults which occur in enlarged glands, etc., get eventually destroyed by inflammatory reaction, so that larvÆ are no longer being produced, while the enlarged gland, etc., which the adults have produced remains. This explanation assumes that the larvÆ of the original worm die in the circulation or elsewhere, e.g., kidney, but we have no evidence as to the duration of life of larvÆ in the human body; but also it assumes that a person cannot be reinfected with filaria, for otherwise there is no reason why the diseased should not be infected in the same proportion as the non-diseased. But assuming the explanation to be true, it would explain why a diseased population show larvÆ in only about one-third of the cases. It must be borne in mind also that the figures are rather small.
Pathology.—In order to explain the effects which do or may be expected to occur from obstruction of lymphatics, it is necessary to have an accurate knowledge of the distribution and connections of
We should recall also that considerable destruction or obstruction of lymphatics or glands may occur without necessarily producing any lymphatic obstruction, at least, of a permanent nature, e.g., when a mass of lymphatic glands is destroyed by a bubo in the groin or, again, when a carcinomatous mass of glands is removed from the axilla. Again, to take the case of chyluria—where it is generally assumed that obstruction must occur higher up than the point at which the intestinal lacteals enter the juxta-aortic glands—this disease may occur, e.g., in temperate regions, quite apart from such obstruction. It is true that some of these cases of chyluria are not cases of chyle in the urine, but, as little or no fat is present, lymphuria. These do not require the above assumption, but seeing that true chyluria may apparently occur without such obstruction, we should be cautious about explaining this and other symptoms on the basis of obstructions which theory may demand, for only too often there are no post-mortem facts at our disposal.
Lymphangitis: What this is due to is unknown. There is no actual evidence of the occurrence of adults in the inflamed vessel. Complete disappearance, not to reappear, of (non-periodic) mikrofilariÆ from the blood has been shown by Bahr and others to occur within twenty-four hours after an attack of lymphangitis, orchitis adenitis or simply a high temperature. This mysterious phenomenon requires explanation. If the mikrofilariÆ were being killed by the attack, their dead bodies should still be found in the blood; or if the adults were being killed, for all we know to the contrary, the larvÆ might well survive. We consider there is no evidence that either are affected, but that for some reason, as little understood as in periodicity, the larvÆ now remain in the organs.
Abscess: In Fiji, by Bahr, they have been found in the substance of various muscles, e.g., quadriceps extensor, latissimus dorsi, serratus magnus, in the popliteal space, groin, axilla, and over the internal condyle of the humerus, and in the upper extremity they are frequently infected with cocci. They not infrequently contain fragments of dead adult filariÆ. Their mode of origin is not clear. They form nearly 30 per cent. of cases of filariasis in Fiji. Of 95 cases, 41 showed mikrofilariÆ in blood, 54 did not.
Hydrocele and enlarged testis: In Fiji they form about 10 per cent. (36 out of 343) of cases of filariasis. The fluid is usually sterile; mikrofilariÆ were present in the fluid in 1 out of 11 cases. In the wall numerous calcified adult filariÆ may be found. The walls consist chiefly of hypertrophied muscle with fibrous tissue, dilated blood-vessels and lymphatics, the lining epithelium of which appears to be
Enlarged glands form over 40 per cent. (153 out of 343) of cases of filariasis, so that they are the commonest expression of filariasis met with in Fiji. The glands are enlarged, fibrotic, and the trabeculÆ are thickened. The lymphatics are thickened or represented merely by fibrous tissue. The gland also shows dilated blood-vessels and numerous spaces filled with lymph. Giant-cells are common in those glands which contain remnants of filariÆ. Masses of lymphocytes enclosed by inflammatory or fibrous tissue are common. Eosinophile cells are also extremely common, not only in the fibrous tissue of the glands, but in other inflammatory or fibrotic conditions: in other organs living or calcified filariÆ are “usually” present. Only about 33 per cent. show mikrofilariÆ in the blood. The epitrochlear gland is frequently enlarged in Fiji.
Breinl has examined enlarged glands and finds loose vascular fibrous tissue with lymphocytic invasion. In parts, the lymphocytes collect into areas 200µ to 800µ in diameter. The lymph tissue surrounding the spermatic cord showed abundance of vessels—(1) large, (2) small. The large had thick walls and wide lumina. In other cases the lumina were nearly filled by a thrombus of newly formed, fine, loose connective tissue.
Varicose glands: In about 7 per cent. (24 out of 343 cases) of filariasis, mikrofilariÆ are found in the blood in 50 per cent. (12 out of 24).
Elephantiasis.—Elephantiasis scroti is associated with hydrocele in 50 per cent. of cases (12 out of 23); in 65 per cent. of cases (15 out of 23) there are associated enlarged glands in one or both groins, though also hydrocele and enlarged glands occur without elephantiasis scroti. In 13 out of 27, i.e., about 50 per cent., cases of elephantiasis in various regions, no associated enlargement of glands is found. Elephantiasis forms in Fiji less than 10 per cent. of cases of filariasis. MikrofilariÆ are present in the blood in 36 per cent. (12 out of 33) of cases.
Chyluria.—Exceedingly rare in Fiji. Theory would demand an obstruction above the point of entry of the lacteals, viz., the pre-aortic lymphatic glands, but in cases in temperate regions it may occur without any such lesion. In some of these cases the fluid is not chyle (fat absent), but presumably lymph. A discussion of the mode of production of chyluria, lymph scrotum, elephantiasis, etc., is at present premature; theory has far outrun fact. Too much stress had been laid on the mechanical action of the worms to the almost total exclusion of their (or possibly their larval) toxic action. The above
Geographical Distribution.—Filaria bancrofti is known in nearly all tropical countries. It occurs in India, China, Indo-China, Japan, Australia, Queensland, the Islands of Polynesia (with the exception of the Sandwich Islands), Egypt, Algeria, Tunis, Madagascar, Zanzibar, Sudan, etc., the south of the United States of America, Brazil, the Antilles, etc. Whether it is the same species in all cases is questionable.
Filaria demarquayi, Manson, 1895.
Syn.: F. ozzardi, Manson, 1897.
Fig. 284.—F. demarquayi: tail, showing paired large fleshy papillÆ. (After Leiper.)
The adult female F. demarquayi measures from 65 to 80mm. in length by 0·21 to 0·25mm. in breadth. The head has a diameter of from 0·09 to 0·1mm. The mouth is terminal. The genital pore opens at 0·76mm. from the head. The alimentary canal is nearly straight and terminates in an anus, which is subterminal. The opening of the anus is marked by a slight papilla. The tail is curved. It rapidly diminishes in size just below the anal papilla. A characteristic pair of fleshy papillÆ project from the tip of the tail. The diameter near the tip of the tail before its termination is 0·03mm. F. demarquayi is a thicker worm than Ac. perstans. It differs from F. bancrofti in the greater size of the head, in the smaller tail, and particularly in the marked fleshy papillÆ at the tip of the tail. These papillÆ are knobby, and not simply cuticular as in Ac. perstans.
The male of Filaria demarquayi has still to be found.
The adult female form of F. demarquayi was found by Dr. Galgey in the body of a native of St. Lucia in whose blood the larvÆ had been found during life. Five adult females were found in the connective tissue of the mesentery.
The larva measures 200µ in length by 5µ in breadth; it is sharp-tailed, and has no sheath. Its movements are very active, and the absence of a sheath enables it to glide along freely all over the slide. It observes no periodicity, being present in the peripheral circulation both by day and by night. As a rule, some eight or ten parasites are found in an ordinary preparation. Sometimes hundreds of these larval filariÆ may be counted on every slide.
The intermediate host has not been discovered.
Geographical Distribution.—St. Vincent, Dominica, Trinidad, and St. Lucia (West Indies), British Guiana, New Guinea (?).
Fig. 285.—Mf. demarquayi in thick film, dried and stained with hÆmatoxylin. 6, unshrunken; 7, shrunken. ×1,000. (After FÜlleborn.)
Filaria taniguchi, Penel, 1905.
Female 68 by 0·2mm. in breadth. Cuticle non-striated. Mouth two pairs of papillÆ. Anus 23mm. from extremity. Vulva 1·3mm. from mouth. Larva 164µ by 8µ, sheathed. Tail truncated. Periodicity nocturnal.
Habitat.—Lymphatic glands of man. Japan.
Fig. 286.—Filaria (?) conjunctivÆ: to the left, life size; to the right, the anterior extremity magnified. (After Addario.)
Filaria (?) conjunctivÆ, Addario, 1885.
Syn.: Filaria peritonei hominis, Babes, 1880; Filaria inermis, Grassi, 1887; Filaria apapillocephata, Condorelli-Francaviglia, 1892.
The female only of this species is known. It measures 16 to 20cm. in length and 0·5mm. in breadth, and is of a whitish or brownish tint. The cuticle is striated with fine transverse and more marked longitudinal striÆ with the exception of a small field surrounding the mouth, which is terminal and has neither papillÆ nor lips. The oesophagus measures 0·6mm. in length. The anus is 3mm. in front of the rounded posterior extremity, and behind it there are two (glandular?) sacs. The vulva is close behind the oral aperture; the vagina soon divides into two convoluted uteri, which are filled with eggs and embryos. Embryos 350µ by 5·
This species (115mm. long) was first observed in Milan by Dubini in the eye of a man; subsequently it was observed, encysted and calcified (190mm. long), by Babes in the gastro-splenic omentum of a woman in Budapest, and finally one (95mm. long) was extracted by Vadela from a tumour the size of a pea in the ocular conjunctiva of a woman in Catania (Sicily), which case has been described by Addario. Possibly Agamofilaria palpebralis, Pace, 1867 (nec Wilson, 1844), and A. oculi humani, v. Nordm., 1832, are the same species.
Fig. 287.—Filaria (?) conjunctivÆ: anterior end greatly magnified; the mouth with the pharynx in the middle; in the cuticle on the right side the opening of the vagina, and behind it the excretory pore. (After Grassi.)
Filaria (?) conjunctivÆ is certainly only an incidental parasite of man; the horse and ass are its normal hosts, but it is not common in these animals, or is frequently confused with Hamularia equi, Gmelin, 1789.
Group. Agamofilaria, Stiles, 1906.
Not a generic but a group name for immature FilariidÆ the development of which does not admit of generic determination.
Agamofilaria georgiana.
Adult unknown, length from 32 to 53mm. Maximum diameter 560µ to 640µ. Head no cephalic cone. Mouth small, circular, surrounded by six papillÆ (two small latero-median and four sub-median). The larger papillÆ are 24µ from base to tip. Excretory pore about 0·5mm. from head. Anus 64µ to 128µ from tip. Cuticle fine striÆ near anus, occasionally elsewhere. Lateral lines clearly marked. Œsophagus 2·5 to 2·9mm. Rectum 200µ long.
Habitat.—Superficial sores on the ankle of a negress, Georgia, U.S.A.
Agamofilaria palpebralis, Pace, 1867 (nec Wilson, 1844).
100 by 1·5mm., removed from a cyst in the left upper eyelid of a boy by Pace, in Palermo.
Agamofilaria oculi humani, v. Nordmann, 1832.
Syn.: Filaria lentis, Diesing, 1851.
The sexless Nematodes observed in the lens of the human eye were termed Filaria oculi humani. Only three cases are known. v. Nordmann observed very small round worms in the lens of a man and woman with cataract, and Gescheidt once found three specimens in the lens of a woman similarly affected.
The demonstration of nematode-like formations in the vitreous remains uncertain even when movements are observed, and when they cannot be extracted and examined microscopically the doubt may occur that one may have mistaken the remains of the hyaloid artery for a worm, which it resembles in form, size and colour; the slightest movement of the eye also causes it to move so that it simulates a living organism.
Accordingly it would be more correct to exclude all the cases known only ophthalmoscopically (Quadri, 1857; Fano, 1868; Schoeler, 1875; Eversbusch, 1891). There then remains only one positive case, described by KÜhnt in 1891. In this case it was possible to follow the gradual growth of the parasite for some time, and the worm, which measured only 0·38mm. in length, was finally extracted.
Agamofilaria labialis, Pane, 1864.
The parasite measures 30mm. in length; the anterior extremity is pointed; the terminal oral aperture is surrounded by four papillÆ; the anus opens 0·5mm. in front of the posterior extremity; the vulva is 2·5mm. in front of the anus; the uterus is double; the anterior one passes with convolutions forward to the cephalic end; the posterior one is directed backwards and remains rudimentary.
Extracted from a small pustule on the inner surface of the upper lip. Also found in Naples by Pierantoni in 1908.
The position of many of these worms is doubtful, and still more so is that of many other imperfectly described “FilariÆ,” which are hardly more than useless and confusing names. These include the following:—
Filaria (?) romanorum-orientalis, Sarcani, 1888.
Observed in the blood of a Roumanian woman; 1mm. in length, 0·03mm. in breadth; tail end pointed, a tongue-like appendage on the head. Eggs the size of a red cell with developed embryo, apparently viviparous.
Filaria (?) kilimarÆ, Kolb, 1898.
Several female specimens, 10 to 20cm. long by 0·5 to 1mm. broad, were once found free in the abdomen of a fallen KitÚ warrior; according to Spengel, who examined them, the oral papillÆ of these worms were similar to those of Dracunculus medinensis. Moreover, Kolb classifies together Nematodes that probably have no connection with each other.
Filaria (?) sp.?
Cholodkowsky calls attention to FilariÆ that are still unknown which cause tumours resembling whitlows on the fingers of peasants of the Twer Government.
Mikrofilaria powelli, Penel, 1905. In Bombay.
Mikrofilaria philippinensis, Ashburn and Craig, 1906. In the Philippines.
Fig. 288.—Setaria equina: left, male; right, female. Natural size. (After Railliet.)
Genus. Setaria, Viborg, 1795.
Syn.: Hamularia, Treutler, 1793; Tentacularia, Zeder, 1800 (nec Bosc, 1797).
Mouth with projecting peribuccal armature deeply notched on the lateral margins, less so dorsally and ventrally. Tail in both sexes with peculiar caudal appendages.
Parasitic in serous cavities, especially of ruminants.
Setaria equina, Abildg., 1789.
Syn.: Gordius equinus, Abildg., 1789; Filaria equi, Gmelin, 1789; Hamularia lymphatica, Treutler, 1793; Tentacularia subcompressa, Zedder, 1800; Filaria papillosa, Rud., 1802; Filaria hominis bronchialis, Rud., 1819; Filaria hominis, Dies., 1851; Strongylus bronchialis, Cobb., 1879.
The body is whitish, filiform, pointed posteriorly. The cuticle presents a delicate transverse striation. The mouth is small, round, and surrounded by a chitinous ring, the border of which carries, at the sides, two semilunar lips, and there is on the dorsal as well as on the ventral surface a papilliform process; on the tail, corresponding with each sub-median line, is a conical papilla. The male measures 6 to 8cm. in length; the posterior extremity ends in a corkscrew spiral; there are on each side four pairs of pre-anal and four or five post-anal papillÆ; the spicules are unequal. The female measures 9 to 12cm. in length and is viviparous; the embryos measure 0·28mm. in length and 0·007mm. in breadth.
Fig. 289.—Setaria equina: anterior end, magnified. (After Railliet.)
Setaria equina is a frequent parasite of horses and asses; it inhabits the peritoneal cavity, and from there occasionally invades the female genitalia or even the liver; it is found more rarely in the pleural cavity or in the cranium. The statement that it also occurs in the subcutaneous connective tissue is probably due to confusion with Setaria (Filaria) hÆmorrhagica, Raill., 1885 (Filaria multipapillosa, Cond. et Drouilly, 1878). Setaria labiata papillosa (immature form) occurs in the eye of the horse, adults in the peritoneal cavity.
Treutler, in 1790, found a filaria in the enlarged bronchial lymphatic gland of a patient suffering from phthisis. It measured 26mm. in
Genus. Loa, Stiles, 1905.
Characterized by the possession of cuticular bosses in both sexes (fig.294).
Loa loa, Guyot, 1778.
Syn.: Filaria oculi, Gerv. et v. Ben., 1859; Dracunculus oculi, Diesing, 1860; Dracunculus loa, Cobbold, 1864; Filaria subconjunctivalis, Guyon, 1864.
Fig. 290.—Loa loa: the anterior end of the male, magnified. (After R. Blanchard.)
Fig. 291.—Loa loa: anterior portion of the female as far as vulva. (After Looss.)
The male measures 25 to 35mm. in length, and 0·3 to 0·4mm. in breadth; the cuticle is not striated, but, with the exception of the anterior and posterior extremities (1·5mm.), is beset with numerous irregularly distributed bosses (4µ to 12µ high by 12µ to 27µ broad). The anterior extremity is somewhat attenuated, and in front is conical and transversely truncated. At the anterior limit of the conical part is a small papilla corresponding with the dorsal and ventral median lines, and a little in front six non-projecting sensory papillÆ (two lateral, four sub-median). Excretory pore 0·65mm. from the anterior end. The posterior extremity is attenuated and somewhat curved ventrally; the anus is 0·082mm. distant from the rounded posterior border. In front of the anus on each side are three globular and pedunculated papillÆ of different sizes, set close one behind the other but asymmetrically; behind the anus on either side are two smaller papillÆ of a different shape; the anterior one resembles the pre-anal papillÆ in form, but is smaller; the posterior one is conical, and rests with a broad base on the cuticle. The spicules are 0·113 and 0·176mm. long.
The female measures 45 to 63mm. in length by 0·5mm. in breadth. It is also beset with irregularly distributed bosses, which in places lie close to each other, and extend to the anterior extremity; posteriorly they become less frequent, but are not entirely absent. The anterior extremity is conical, the posterior one straight, attenuated, rounded off, 0·17mm. from the anus. The uteri contain eggs in the most various stages of development, as well as hatched-out larvÆ, 253µ to 262µ in length and 4·7µ to 5µ in breadth. The vulva lies about 2mm. from the head end. The vagina, 9mm. long, divides into two branches, which at first run posteriorly and parallel to one
Fig. 292.—Loa loa in situ. Natural size. (After FÜlleborn and Rodenwaldt.)
Fig. 293.—Loa loa: male on the left, female on the right. ×2. (After Looss.)
Unsegmented eggs measure 32µ by 17µ, in the morula stage 40µ by 25µ, and when containing embryos 50µ by 25µ. The vitelline “shell” of the egg is, according to most authors, stretched by the embryo and becomes the sheath of the hatched larva. While
Fig. 294.—Loa loa: on the left, the hind end of a male; on the right, of a female. Note the cuticular bosses shown in the figure of the female. ×285. (After Looss.)
Fig. 295.—Loa loa: lateral view of tail of male showing papillÆ. (After Lane and Leiper.)
Fig. 296.—Loa loa. a, ventro-lateral aspect of tail showing papillÆ and one spicule; b and c, terminations of the two spicules. (After Leiper.)
Site of Worms.—In various localities; under the muscular aponeuroses on extensor surfaces of arms and legs, fingers, trunk, eyelid, conjunctiva, frÆnum linguÆ, penis, pericardium, anterior chamber of eye, and, according to some authorities, in lymphatic vessels, e.g., those of spermatic cord. As many as thirty adults may be found. The worms appear to be frequently immature, and it has been stated that worms in superficial parts are immature, those situated deeply are mature, but the data are few.
The first accounts of Loa loa—long since forgotten—were reported by Pigafetta, and are contained in a book of travels on the Congo printed in 1598. In an accompanying illustration is depicted, not only the ancient method of extraction of the Medina worm, but also the operative removal of the filaria from the conjunctiva. Subsequently the presence of the worm in negroes was confirmed by Bajon in Guiana (1768) and by Mongin in Mariborou (San Domingo), likewise in a negro (1770). At about this time a French ship’s doctor, Guyot, was cruising on the West Coast of Africa; he observed the parasite termed “loa” by the natives, and learned that it was frequent in the negroes of the Congo district. Since that time numerous observations have been reported. It was formerly common in South America, where the parasite was imported by slaves, but it disappeared when the traffic ceased; it was particularly prevalent in the Congo, where it occurs not only in natives, but also in Europeans. During recent times it has repeatedly been observed in Europe in negroes as well as in white men who have lived on the West Coast of Africa.
Nematodes of different size have been repeatedly observed in the eye of man, in the anterior chamber, lens and vitreous. For example, Mercier, in 1771 and 1774, removed a filaria out of the anterior chamber of two negroes in St. Domingo. One was 36mm. long. Barkan, in 1876, in San Francisco, removed one from the eye of an Australian. Again, Cappez and Lacompte, in Brussels, in 1894, observed for some weeks immature Nematodes in the eye of a negro girl, aged 2 12 years, and then removed them. What these Nematodes actually were in these cases it is impossible to say.
Structure of LarvÆ.—In dried films the larva varies in size from 140·5µ to 166·5µ, average, 152·5µ; while another set of measurements gave the values 131µ, to 150µ, average, 143·6. In films fixed with hot alcohol the dimensions were 208µ to 254µ, average, 231µ.
The nerve ring 21·4 to 21·8 per cent. Excretory pore 30·4 to 31·8 per cent. Excretory cell 34·8 to 37·3 per cent. G1 cell 68·2 to 68·5 per cent. Anal pore 81·6 to 82·4 per cent. of total length. For other details cf. Filaria bancrofti.
Fig. 297.—Mf. loa: in thick film, dried and stained with hÆmatoxylin. ×1,000. (After FÜlleborn.)
LarvÆ in Blood.—These from their diurnal periodicity are known as Mikrofilaria diurna. The evidence that these larvÆ are the young of the adult worm Loa loa is: (1) They are identical in structure with
Periodicity.—Here, as in the case of the larvÆ of Filaria bancrofti, the larvÆ that appear in the blood are probably the overflow simply of the larvÆ which we assume, on analogy, to have their principal site in the lungs. They appear in the blood about the time of getting up, 6 to 8a.m. (10 in 20 mm.3), at 12 noon there are twenty-four, at 8p.m. the number has fallen to eighteen, and at midnight to one, while from 2a.m. to 6a.m. none, or one only, may be found. This periodicity is, as a rule, a very constant one, but there are exceptions, and in certain cases more have been found at midnight than at 9a.m. The periodicity is also lost in pathological conditions, e.g., sleeping sickness (vide also under Filaria bancrofti). The possibility of non-periodic Loa loa larvÆ should also be considered.
Pathology.—The parasite wanders about the body, and may be seen under the skin in thin parts. Their advance is in some cases at the rate of an inch in two minutes. During their progress they give rise to creeping sensations and to a condition of transient oedematous areas known as Calabar swellings on various parts of the body, e.g., arm. These vary in diameter from 1 to 10cm., and often shift their position an inch or so a day. They give rise to a certain amount of redness, tension and heat, and their development is promoted by muscular action of the part. They disappear to reappear elsewhere. The condition is associated with a high eosinophilia, 50 per cent. being not uncommon. Patients known to harbour
Not uncommonly Mikrofilaria perstans occurs in the blood together with M. diurna.
Duration of Life.—This is long, as some cases have been observed five to six years after leaving Africa. The incubation period is about a year.
Life-history.—Development of the larvÆ takes place in the salivary glands of Chrysops sp. as shown by Leiper.
Geographical Distribution.— West Africa, especially in Congo.
Genus. Acanthocheilonema, Cobbold, 1870.
Cuticle striated longitudinally. Œsophagus divided into two portions. Tail in both sexes with short lateral conical cuticular appendages. Spicules unequal, the larger membranous distally, the smaller hooked. Vulva in oesophageal region.
Acanthocheilonema perstans, Manson, 1891.
Syn.: Filaria perstans, P. Manson, 1891; Filaria sanguinis hominis var. minor, Manson, 1891.
The adult female Ac. perstans measures 70 to 80mm. in length by 120µ to 140µ in breadth. The head is club-shaped and measures 0·07mm. in diameter. The vulva opens at 0·6 to 1·0mm. from
Fig. 298.—Acanthocheilonema perstans. 1, tail of male; 2, tail showing cuticular flaps devoid of fleshy contents. (After Leiper.)
Fig. 299.—Mf. perstans in thick film, dried and stained with hÆmatoxylin; 4, unshrunken; 5, shrunken. ×1,000. (After FÜlleborn.)
The adult male measures 45mm. in length by 60µ to 80µ in breadth. The diameter of the head is 0·04mm. The tail is much curved. There are four pairs of pre-anal papillÆ and two pairs of post-anal papillÆ. Spicules very unequal in size. Cloaca 121µ from the tail end. At the tail end two triangular cuticular appendages.
The adult worms inhabit the connective tissue at the base of the mesentery, especially in the region of the pancreas, abdominal aorta and suprarenals. To find them the mesentery should be removed, placed in a 2 per cent. solution of formalin, and then carefully examined at leisure.
Mikrofilaria perstans.—160µ to 210µ by 5µ to 6µ broad. Has no sheath. Cuticle transversely striated. Tail rounded off, not pointed. Nerve ring at 34µ. Excretory pore 49µ, genital pore 125µ from head. Smaller larvÆ 90µ to 110µ by 4µ broad. A “fang” is also described on the head.
| Mf. perstans. | Mf. demarquayi. |
| (1) Tail stumpy. | (1) Tail pointed. |
| (2) Column of nuclei extends to tip of tail. | (2)Doesnotextendtotip. |
Periodicity.—None.
Life-history.—Unknown.
Geographical Distribution.—Very common in many parts of Africa: Sierra Leone, Dahomey, Northern Nigeria, Southern Nigeria, Cameroons, Ivory Coast, Gold Coast, Old Calabar, Congo, Uganda. Absent from Zululand, Basutoland. On the East Coast of Africa it is not found in the towns of Zanzibar and Mombasa, neither is it found in the country of the Masi, nor amongst the Kavirondo, who dwell along the north-east shores of Lake Victoria.
In South America, Ac. perstans is very common amongst the aboriginal Indians in the interior of British Guiana. However, it is not found in Georgetown and in New Amsterdam, neither is it found in the cultivated strip of coast lying between these two towns, but it is common on the coast farther north near the Venezuelan boundary, where the forests stretch to the sea. The Waran Indians, who live at the mouth of the Waini river, harbour this parasite. It is absent in the West Indies.
Topographically, Ac. perstans is found only in areas covered by dense forest growth and abounding in swamps. In Kavirondo, where the forest disappears and the land is covered with scrub and short grass, it is not found; likewise it is not found on the grassy plains of the highlands of British East Africa. Towns and cultivated areas are free from it.
Genus. Dirofilaria. Railliet and Henry, 1911.
Body very long, thread-like, cuticle transversely striated. Mouth with six papillÆ. Male tail spiral with voluminous pre-anal and some large post-anal papillÆ; spicules unequal. Vulva near the anterior hundredth of body; viviparous. Parasitic in heart or blood-vessels and subcutaneous tissue.
Dirofilaria magalhÃesi, R. Blanchard, 1895.
Syn.: Filaria bancrofti, v. Linstow, 1892; Filaria bancrofti, P.S. de MagalhÃes, 1892 (nec Cobbold, 1877).
Fig. 300.—Dirofilaria magalhÃesi: posterior extremity. (After v. Linstow.)
The male measures 83mm. in length by 0·28 to 0·40mm. in breadth. The anterior extremity is rounded, and has no papillÆ (?6); the posterior extremity exhibits a double curve, with four pre-anal and four post-anal papillÆ on each side. These are large and have a villous appearance. The mouth is round and unarmed, the pharynx measures 1mm. in length, is cylindrical, very muscular, and its hinder part is dilated. The anus is situated 0·11mm. in front of the hind end. There are probably two unequal spicules; one only, however, is known—apparently the shorter one—the length of which is given as 0·17 to 0·23mm.
The female measures 155mm. in length and 0·6 to 0·8mm. in breadth; the rings of the cuticle are 0·005mm. apart (in the male 0·003mm. apart); the anterior extremity is slightly thickened and club-like, the posterior extremity is slender, and terminates obtusely; the lateral line is 0·127mm. in breadth (that of the male 0·007 to 0·008mm.); the anus opens 0·13mm. in front of the hind end, the vulva is 2·5mm. distant from the mouth, the ovaries are two much convoluted tubes. The eggs measure 38µ by 11µ.
This species was first discovered at a post-mortem, in the left ventricle, by J.P. Figueira de Saboia in Rio de Janeiro, and has been described by P.S. de MagalhÃes.
D. immitis occurs in the right ventricle of the heart of the dog in Europe and the Tropics.
D. repens is also a common subcutaneous Nematode in dogs in Annam.
Sub-family. OnchocercinÆ, Leiper, 1911.
Cuticle with spiral thickenings.
Genus. Onchocerca, Diesing, 1841.
Male with four pre-anal papillÆ. Female with vulva situated anteriorly.
Onchocerca volvulus, R. Leuckart, 1893.
Syn.: Filaria volvulus, R. Leuckart, 1893.
The adult male measures 30 to 35mm. in length by 0·14mm. in breadth. The body is white, filiform, attenuated at both ends. The head is rounded and has a diameter of 0·048mm. The cuticle
The adult female is of uncertain length, but much longer than the male, probably about 10 to 12cm. The head is rounded and truncated; it measures 0·065mm. in diameter. The tail is curved. The vulva opens 0·55mm. from the head. The hand-like cuticular thickenings are well marked. Eggs ovoid with a prolongation at each pole “like an orange wrapped in tissue paper.” The larva measures about 300µ by 7µ to 8µ; it has no “sheath.” The body tapers from about the last fifth of its length, and terminates in a sharply pointed tail. At about the anterior fifth of the body there is a V spot.
O. volvulus is found in peculiar subcutaneous tumours, the size of a pea to that of a pigeon’s egg. The same patient may present one or several of these tumours. The regions of the body most frequently affected are those in which the peripheral lymphatics converge. Thus they are usually found in the axilla, in the popliteal space, about the elbow, in the sub-occipital region and in the intercostal spaces. The tumours are never adherent to the surrounding structures, and can be easily enucleated. They are formed of a dense connective tissue wall and internally a looser fibrous meshwork. This is traversed by a series of canals in which the worms lie, but they are also partly embedded in the denser wall. The canals apparently dilate into cavities filled with slimy pus-like fluid consisting largely of larvÆ. According to Brumpt the posterior extremity of the male, and the anterior extremity of the female with its vaginal opening, are free in one of the spaces for the purpose of copulation and parturition. If a tumour be cut into and placed in salt solution, Rodenwaldt states that the undamaged males wander out into the solution.
The formation of the tumours is elucidated by Labadie-Lagrave and Deguy’s case. The authors found an immature female Onchocerca volvulus in a lymphatic vessel partly obstructed by an infiltration of fibrin and leucocytes. It appears, therefore, that the presence of the parasites within the lymphatics gives rise to an inflammatory process, and that the consequent fibrinous deposit envelops the parasites, obliterates the lumen of the vessel, and ultimately isolates the affected tract. At any rate, in young tumours the worms appear to lie in a structureless substance permeated by leucocytes in which connective tissue is gradually organized from the periphery, thus isolating the worms.
In cases of infection with O. volvulus larvÆ have been found by Ouizilleau, FÜlleborn, and Simon in lymph glands, and in the finger blood if considerable pressure is used so as to squeeze lymph out of the tissues. They are sheathless, and the following are the dimensions in ordinary dried films: Length, 274µ; nerve ring, 23·7 per cent.; G1 cell, 69·6 per cent.; end of last tail cell, 96·3 per cent. The dimensions of larvÆ of O. volvulus taken from the uterus and prepared in the same way are: Length, 224·5µ; nerve ring, 24·3 per cent.; G1 cell, 68·9 per cent.; end of the last tail cell, 95·5 per cent. In all probability the larvÆ in the glands and blood are those of O. volvulus.
According to the natives, the tumours may last indefinitely and never ulcerate. Some old patients told Brumpt that their tumours had been present since childhood. Probably Onchocerca volvulus, like some other FilariidÆ, may live for many years.
O. volvulus occurs in various parts of West Africa: Gold Coast, Sierra Leone, Dahomey, Lagos, Cameroons. Brumpt, on the banks of the Welle between Dongon and M’Binia (Belgian Congo), found about 5 per cent. of the riverine population affected.
Family. TrichinellidÆ, Stiles and Crane, 1910.
Sub-family. TrichurinÆ, Ransom, 1911.
Male with a single long spicule, with sleeve-like sheath. One ovary. Eggs with an opening at each pole closed by a plug-like operculum. Eggs hatch on being swallowed by a new host. Genera: Trichuris, Capillaria.
Genus. Trichuris, RÖderer and Wagler, 1761.
Syn.: Trichocephalus, Goeze, 1782 (nec Trichiurus, L., 1758); Mastigodes, Zeder, 1803.
The anterior part of the body is very long and thread-like; the posterior, much shorter part, is thicker, rounded posteriorly, and the anus is terminal. The males have the posterior extremity spirally rolled; the vulva is situated at the commencement of the posterior part of the body. The Trichocephali live in the large intestine of mammals, the cÆcum by predilection; their development is direct, infection occurs through the ingestion of embryo-containing eggs.
Trichuris trichiura, LinnÆus, 1761.
Syn.: Trichocephalus trichiurus, L., 1771; Ascaris trichiura, L., 1771; Trichocephalus hominis, Schrank, 1788; Trichocephalus dispar, Rud., 1801.
Fig. 301.—Trichuris trichiura: on the left, male; on the right, female with the anterior extremity embedded in the mucous membrane of the intestine; below, egg.
The male measures 40 to 45mm. in length, the spicule is 2·5mm. long, its retractile sheath is beset with spines. The female measures 45 to 50mm. in length, of which two-fifths appertain
The whip worm is one of the most common parasites of man and appears to be distributed over the entire surface of the globe; it is, however, more frequent in the warmer regions. It is found in persons of both sexes and all ages with the exception of infants. In autopsies it is found in the following numbers: In Dresden in 2·5 per cent., in Erlangen in 11·1 per cent., in Kiel in 31·8 per cent., in Munich in 9·3 per cent., in Petrograd in 0·18 per cent., in GÖttingen in 46·1 per cent., in Basle in 23·7 per cent., in Greenwich in 68 per cent., in Dublin in 89 per cent., in Paris in about 50 per cent., and in Southern Italy in almost 100 per cent. On examining the fÆces the eggs of the whip worm were found as follows: In Munich in 8·26 per cent., in Kiel in 45·2 per cent., in Greifswald in 45 per cent., in North Holland in 7 per cent., in Novgorod in 26·4 per cent., in Petrograd in 5 per cent., in Moscow in 5·3 per cent.
The development of the eggs is completed in water or in moist soil, and occupies a longer or shorter time according to the season; the eggs possess great powers of resistance, as do the larvÆ, which, according to Davaine, may remain as long as five years in the eggshell without losing their vitality. Leuckart proved by experiment that direct infection with Trichuris ovis (Ovis aries) and T. crenata (Sus scrofa dom.) was produced by embryo-containing eggs; Railliet obtained the same results with T. depressiuscula of dogs, and Grassi subsequently, by means of two experiments, demonstrated the direct development of Trichuris trichiura. In one case embryo-containing eggs were swallowed on June 27, 1884, and on July 24 the ova of Trichocephali were found in the fÆces for the first time.
Trichuris trichiura is found not only in man, but also in various monkeys (T. palÆformis, Rud.), as well as in lemurs (T. lemuris, Rud.).
Other species are T. crenata in pig; T. ovis in cattle, sheep, goat, and pig (?); T. depressiuscula in dog; T. campanula in cat; T. unguiculata in rabbit and hare; T. cameli in camel; T. discolor in humped cattle; T. nodosus in mouse; T. alcocki in the thamin (India); T. globulosa in camel; T. giraffÆ in giraffe.
Sub-family. TrichinellinÆ, Ransom, 1911.
Male without spicule; females ovoviviparous. LarvÆ penetrate muscles of host and become encysted. Genus: Trichinella.
Genus. Trichinella, Railliet, 1895.
Syn.: Trichina, Owen, 1835 (nec Meigen, 1830).
Very small TrichinellinÆ, the males of which have two conical appendages at the caudal extremity; the vulva is situated at the border of the anterior fifth of the body. There is only one species.
Trichinella spiralis, Owen, 1835.
Syn.: Trichina spiralis, Owen, 1835.
The male measures 1·4 to 1·6mm. in length and 0·04mm. in diameter. The anterior part of the body is narrowed, the orifice of the cloaca is terminal and lies between the two caudal appendages; internal to these are two pairs of papillÆ, dorsal one behind the other. The cloaca is evertible for copulation. The females measure 3 to 4mm. in length and 0·06mm. in diameter; anus terminal.
Trichinella spiralis in its adult stage inhabits the small intestine of man, pig, wild boar, rat. The young do not leave the body of the host but become encysted in the muscles. Experimentally it develops in the black rat (Mus rattus), the sewer rat (M. decumanus), the domestic pig (Sus scrofa dom.), the wild boar (Sus scrofa ferox), the domestic dog (Canis familiaris), the fox (C. vulpes) the badger (Meles taxus), the polecat (Putorius foetidus), the marten (Mustela foina), the raccoon (Procyon lotor), the hippopotamus and the cat, and many other mammals (rodents and carnivora); TrichinellÆ have been artificially introduced, by administering the encysted stage, into the dog, the mole (Talpa europÆa), the mouse (Mus musculus), the hare (Lepus timidus), the rabbit (L. cuniculus), the hedgehog (Erinaceus europÆus), the marmot (Cricetus vulgaris), the vole, the dormouse, the sheep, the calf, the horse, etc. Human beings and the pig, rat, mouse, guinea-pig and rabbit are most easily infected; less easily the sheep, calf and horse; with difficulty the cat, dog and badger. Trichinella can also be reared in birds (fowl, pigeon and duck), but the young do not
Fig. 302.—Trichinella spiralis. ?, mature female: E, embryos; V, vulva; Ov, ovary. ?, mature male: T, testes. c., newly born larva. d., larva in the muscles. e., encapsuled larva in the muscles. Magnified. (After Claus.)
History.—Encapsuled TrichinellÆ had been observed in London by Peacock (1828) and by J. Hilton (1833) in the muscular system of man; soon after (1835), Paget found them in London in an Italian who had died of tuberculosis, and recognized them to be encysted entozoa, which R. Owen described as Trichina spiralis. Soon after, some further observations were reported on the occurrence of encysted TrichinellÆ, in man, in England, Berlin, Heidelberg, Denmark, North America; they were also found in the pig (Leidy, Philadelphia) and the cat (Herbst, GÖttingen, and Gurlt, Berlin). Herbst even succeeded in infecting a badger with encysted TrichinellÆ, and subsequently infected two dogs with the flesh of this badger (1850). In 1855 R. Leuckart (Giessen) also commenced feeding experiments, and, like KÜchenmeister and Virchow (1859), first went on the wrong track because it was believed at that time that TrichinellÆ were the larvÆ either of Trichocephalus or Strongylus. Nevertheless, these experiments yielded some important results; they showed that TrichinellÆ become adult in the intestine within a few days, and that the females are viviparous (Leuckart). Until that time TrichinellÆ had been regarded as fairly harmless guests of man, but opinions soon changed when Zenker in Dresden (January, 1860), in performing the autopsy of a girl, aged 10, who had entered the hospital with typhoid symptoms and there died, found TrichinellÆ (not yet encysted) in the muscles; the intestinal lesions characteristic of typhoid were lacking, but numerous adult TrichinellÆ were found in the intestine. Inquiries elicited the fact that at about Christmas time the girl had been taken ill after eating pork, and at the same time the butcher from whom the meat was bought as well as several of his customers fell sick: the pickled pieces of the same meat were full of TrichinellÆ. In the face of this information it was not difficult to ascertain the cause of the disease and the manner of infection in Zenker’s case, and it was not long before Leuckart, Virchow and Zenker were able by renewed experiments to demonstrate the cycle of development of Trichinella spiralis. Similar investigations followed by Claus in WÜrzburg, Davaine in Paris, Fuchs and Pagenstecher in Heidelberg, etc.
Hardly had Zenker’s case been published than numerous observations on trichinosis in man appeared, some referring to isolated cases, others to small or great epidemics, and nearly all from North Germany. The worst epidemic was that of Hadersleben (1865), in which place, numbering hardly 2,000 inhabitants, 337 persons were taken ill within a short time, and of these 101 died. The source of infection proved to be a single pig, the flesh of which had been mixed with that of three other pigs; 200 of the badly infected persons had exclusively eaten raw pork.
Moreover, it soon became clear that epidemics of trichinosis had been observed in Germany prior to 1860, but that their nature had not been recognized, although in a few cases TrichinellÆ had been found in the muscles of those who had succumbed.
History of the Development of Trichinella spiralis.
Shortly after their introduction into the intestine of experimental animals the encysted TrichinellÆ escape from their capsules, which are destroyed by the gastric juices, and they then enter the duodenum
The young brood is distributed from the heart throughout the entire body, but the conditions necessary to its further development are found only in striated muscle; the young Nematodes penetrate the capillaries, attain the intramuscular connective tissue and then invade the fibres (Virchow, Leuckart, Graham304). On the ninth or tenth day after infection the first TrichinellÆ have reached their destination; but further invasions are constantly taking place because the intestinal TrichinellÆ live from five to seven weeks, and continue to produce their young.
Symptoms.—(1) Period of invasion: Gastro-intestinal symptoms—nausea, vomiting, watery diarrhoea, colic. Muscular pains may occur even at this period. Recurrent abdominal pains about the eighth day, a temporary oedema. Embryos are abundant in the serous cavities.
(2) Period of dissemination: Second week. Myositis, variable in amount, is the predominant symptom. The biceps and calf may be hard and tender. Mastication, speech, respiration, etc., may be difficult and painful. Dyspnoea may be intense. Temperature 104° to 105°F.
(3) Period of encystment: Symptoms of marked cachexia. Third week: Second period of oedema, especially of face. Delirium, somnolence, lung affections. Death or gradual subsidence of symptoms in mild cases.
Eosinophilia (50 per cent. or more) is present.
In consequence of the new batches of young produced during several weeks, the above-mentioned symptoms of disease are often considerably aggravated; the fever increases, delirium may arise, and infiltration of the lungs, fatty degeneration of the liver and inflammation of the kidneys may ensue; the initial slight oedema may extend, the strength dwindles, and in many cases the patients succumb to the trichinosis. In severe cases improvement of the condition is only apt to occur in the fourth or fifth week; the convalescence is always protracted.
Fig. 303.—A., isolated muscular fibre of a rat, invaded by Trichinella. 510/1. B., section through the muscle of a rat; the infected fibre has lost its transverse striation; its nuclei are enlarged and multiplied. 310/1. C., portion of a Trichinella capsule, at the pole of which connective tissue cells are penetrating the thickened sarcolemma. (After Hertwig-Graham.)
The muscular fibres attacked degenerate, the transverse striation at first disappearing; the fibres then assume a granular appearance, the nuclei multiply and become enlarged, and are surrounded by an area of granular material, which stains more deeply than the remaining contents of the sarcolemma. Two or three weeks after infection, the spirally rolled-up TrichinellÆ have grown to 0·8 to 1·0mm., and in their vicinity the muscular fibre is swollen, spindle-shaped, and the
Later on fat cells appear at their poles, and after about six or nine months they commence to calcify, the process starting at the poles (fig.305). Finally, sometimes after the lapse of years, the captive TrichinellÆ themselves become calcified.
Fig. 304.—Calcified Trichinella in the muscular system of a pig; the capsules are not calcified. (After Ostertag.)
Fig. 305.—Various phases of the calcification of Trichinella of the muscles, which starts at the poles of the capsule.
According to experience, TrichinellÆ are not evenly distributed in the muscular system of pigs; the diaphragm, the muscles of the larynx, tongue, abdomen and intercostal spaces are their favourite positions; this predilection for the respiratory muscles is explained by their regular contractions, owing to which regular narrowings of the capillaries take place, thus favouring the settling of the circulating TrichinellÆ. The same circumstance probably explains the frequency of the parasites in the tongue.
Possibly also the TrichinellÆ that bore direct through the intestine may, from the abdominal cavity, penetrate the muscles in the vicinity. Frequently also encysted TrichinellÆ are found in remarkable numbers
The TrichinellÆ, in their encysted condition, may remain alive and capable of development for many years—in the pig eleven years and in man as much as twenty-five to thirty-one years. Encystment, however, is not a necessary condition for the development of the brood, that is to say, TrichinellÆ which reach the gut of suitable animals become sexually mature and multiply provided that they have developed so far as to possess a rudimentary genital spot, which occurs when the body is 0·5 to 0·75mm. long, but all the same a great part of non-encapsuled TrichinÆ perish on their passage through the stomach.
The black rat (Mus rattus), and more particularly the sewer rat (Mus decumanus305), are the normal hosts of Trichinella spiralis. These animals, especially the last-named species, infect themselves very easily, as they are cannibalistic, and they also transmit trichinosis to other species by which they are devoured, such as pigs, dogs, cats, foxes, bears and martens. Rats are infected also by the ingestion of fÆcal matter from infected animals which contains trichinÆ (HÖyberg). Man becomes infected with Trichinella by eating the flesh, insufficiently cooked, of infected pigs, also, but more rarely, by eating the infected flesh of wild boars, dogs, cats, bears and foxes.
The infection of pigs may likewise take place by their having access to the offal of trichinous pigs, or being actually fed on it. These are, however, exceptions, which, as a matter of course, are of great importance in certain places. As a matter of fact, the rats examined for Trichinella were always found to be severely infected. Thus Billings, in the knackers’ yard at Boston, found that 76 per cent. of the rats were infected, and in an export slaughterhouse 100 per cent. were found to harbour the parasite; in the city of Boston 10 per cent. of the rats had trichinosis. Heller found that of 704 rats, from twenty-nine different places in Saxony, Bavaria, WÜrtemberg and Austria, 8·3 per cent. were infected with TrichinellÆ; of the rats caught in the knackers’ yards, 22·1 were diseased; of those taken in slaughterhouses, 2·3 were infected, and of rats from other localities only 0·3 per cent. harboured the parasite. Leisering found almost the same figures, but in rats from slaughterhouses 5·3 per cent. were infected.
The geographical distribution of T. spiralis does not correspond with the occurrence of trichinosis in man; local customs are
This report, according to the researches of H.U. Williams, must be considerably modified. This author has examined the muscular system of human cadavers according to the method employed by inspectors of meat for pigs. The investigations were conducted in the Pathological Institute of the University of Buffalo, and the observer has examined 505 bodies since 1894, of which 27 (= 5·34 per cent.) were invaded by Trichinella. The cases, according to the nationality, are divided as follows:—
| Examined | Trichinella | Percentage of positive results | |||
| Absent | Present | ||||
| Americans: | |||||
| (a) Whites | 207 | 201 | 6 | 2 | ·89 |
| (b) Negroes | 70 | 65 | 5 | 7 | ·14 |
| British and Irish | 62 | 57 | 5 | 8 | ·06 |
| Canadians | 12 | 10 | 2 | 16 | ·66 |
| Germans | 49 | 43 | 6 | 12 | ·24 |
| Italians | 12 | 10 | 2 | 16 | ·66 |
| Other nationalities | 27 | 27 | 0 | 0 | |
| Nationality unknown | 66 | 65 | 1 | 1 | ·51 |
| Total | 505 | 478 | 27 | 5 | ·34 |
It is worthy of remark that half of all the positive cases were mental patients, who were found to be affected with Trichinella to well-nigh 12 per cent. Trichinosis was not, however, the cause of death in any case. Very frequently the TrichinellÆ were found calcified and dead.
Conditions are similar in most countries of Europe, where, of course, the number of infected pigs is considerably smaller, but the disease depends less on this than on the way in which the pork is prepared.
Cases of trichinosis have been known to occur in nearly all the countries of Europe; further, in Egypt, Algeria, East Africa, Syria, India, Australia, and America. North Germany, more
Prophylaxis.—The grave nature of the disease and the comparatively high mortality relating to trichinosis led the authorities to adopt certain preventive measures, which are the more necessary as national customs cannot be altered in a short time. As the usual process of pickling and smoking, even when long continued, does not certainly ensure the death of the TrichinellÆ contained in the meat, and also because in roasting and boiling large pieces of pork a considerable time is necessary to permit the temperature required to kill off the parasites (62° to 70°C.) to penetrate to the middle of the joint, it appeared to be most practical to have all pigs microscopically examined for TrichinellÆ before they, or parts of them, were placed on the market, and all infected meat condemned, no matter whether the TrichinellÆ were present in large or small numbers, still undeveloped or calcified. Since 1877 obligatory examination of pork has been introduced in Prussia, though as yet it is not thoroughly carried out; other states of North Germany as well as the larger towns of South Germany soon followed; a complete army of trichina inspectors, officially examined and periodically controlled by experts, and whose number in Prussia amounted to 27,602 in 1896, this being even increased to 28,224 in 1899, have the charge of examining pork on certain lines laid down. These are at the present time uniformly administered. The proceeding is usually that the trichina inspector himself goes to the slaughterhouses, or special samplers take pieces of the muscles that are known to be the favourite seats of the parasite (pillars of the diaphragm, the costal part of the diaphragm, muscles of the tongue and larynx, intercostal and abdominal muscles); six small portions are separated from each piece, pressed between slides or special compressors, and carefully gone through by examining them with a low power of the microscope. The pigs free from TrichinellÆ are passed for commerce; trichinous pigs, on the other hand, in Prussia, are only allowed to be used for industrial purposes, i.e., the hide and bristles are used, the fat is allowed to be melted down, or certain parts are used for the manufacture of soap or glue. In Saxony, however, it is still permitted to place trichinous flesh on the market, fully declaring its nature, and after having been heated to its deepest strata at a temperature of 100°C. in a suitable apparatus, and under the supervision of a veterinary surgeon.
As to the proportion of trichinous pigs to healthy ones, the following tables give the figures for Prussia:—
| Year | Number of pigs examined | Number of trichinous pigs | Proportion |
| 1878 | 2,524,105 | 1,222 | 1:2,065 |
| 1879 | 3,164,656 | 1,938 | 1:1,632 |
| 1881 | 3,118,780 | 1,695 | 1:1,839 |
| 1882 | 3,808,142 | 1,852 | 1:2,056 |
| 1883 | 4,248,767 | 2,199 | 1:1,932 |
| 1884 | 4,611,689 | 2,624 | 1:1,741 |
| 1885 | 4,421,208 | 2,387 | 1:1,852 |
| 1886 | 4,834,898 | 2,114 | 1:2,287 |
| 1887 | 5,486,416 | 2,776 | 1:1,988 |
| 1888 | 6,051,249 | 3,111 | 1:1,945 |
| 1889 | 5,500,678 | 3,026 | 1:1,818 |
| 1890 | 5,590,510 | 1,756 | 1:3,183 |
| 1891 | 6,550,182 | 2,187 | 1:2,996 |
| 1892 | 6,234,559 | 2,085 | 1:2,992 |
| 1896 | 8,759,490 | 1,877 | 1:4,666 |
| 1899 | 9,230,353 | 1,021 | 1:9,040 |
| 1902 | 9,093,210 | 725 | 1:12,397 |
The proportion, however, is not only subject to variation in separate years, but differs according to the district; thus, in 1884, in the state district of Minden there was one trichinous pig to 30,146 healthy animals, in Erfurt 1 to 14,563, in the district of Gnesen 1 to 101, in Schrimm 1 to 86, and in Schroda 1 to 68.
In Germany Trichinella is becoming LESS COMMON in pigs (Ostertag):—
| (a) Prussia. | |||||
| Year | Pigs found to be trichinous | ||||
| 1878–1885 | 0· | 061– | 0·048 | per cent. | |
| 1886–1892 | 0· | 033– | 0·043 | " | |
| 1896 | 0·021 | " | |||
| 1899 | 0·014 | " | |||
| 1902 | 0·011 | " | |||
| (b) Saxony. | |||||
| Year | Number of pigs found to be trichinous | ||||
| 1891 | 0· | 014 | per cent. | ||
| 1892 | 0· | 011 | " | ||
| 1893 | 0· | 008 | " | ||
| 1894 | 0· | 007 | " | ||
| 1895 | 0· | 012 | " | ||
| 1896 | 0· | 0102 | " | ||
| 1899 | 0· | 004 | " | ||
| 1902 | 0· | 0056 | " | ||
| (c) City of Berlin. | |||||
| Year | Number of pigs found to be trichinous | ||||
| 1883–1893 | 0· | 035– | 0·064 | per cent. | |
| 1893–1897 | 0· | 022– | 0·015 | " | |
| 1902 | 0· | 006 | " | ||
There is no doubt that the excellent preventive measure of official inspection for Trichinella has led to the avoidance of grave disasters; its introduction has not yet caused an entire cessation of trichinosis in man, because inspection of pork is not obligatory
In addition private prophylaxis must not be neglected, and its chief aim should be directed to the suitable preparation of pork.
Family. DioctophymidÆ.
Genus. Dioctophyme, Collet-Megret, 1802.
Syn.: Eustrongylus, Dies., 1851.
Large worms. Anterior extremity unarmed; the mouth is surrounded by six papillÆ. One ovary. The vulva is in the anterior region of the body.
Dioctophyme gigas, Rudolphi, 1802.
Syn.: Dioctophyme renale, Goeze, 1782; Ascaris canis et martis, Schrank, 1788; Ascaris visceralis et renalis, Gmelin, 1789; Strongylus gigas, Rud., 1802; Eustrongylus gigas, Dies., 1851; Strongylus renalis, Moq. Tand., 1860; Eustrongylus visceralis, Raill., 1885.
Fig. 306.—Dioctophyme gigas, male. Natural size. (After Railliet.)
Colour blood-red; the anterior extremity somewhat slender; there is a series of about 150 papillÆ along the lateral lines; the sub-median lines are strongly developed, and from them spring the radial muscles for the intestine.
The males attain a length of 40cm. and a diameter of 4 to 6mm.; the posterior extremity is transversely truncated; the anal orifice is within the base of the collar-like bursa, the thickened edges of which are beset with papillÆ; the spicule measures 5 to 6mm. in length.
Fig. 307.—Eggs of Dioctophyme gigas; above seen from the flat, below in optical section. 400/1. (After Railliet.)
The females attain a length of 100cm. and a breadth of 12mm. The anus is crescent-shaped and terminal. The vulva is 50 to 70mm. distant from the anterior extremity. The eggs are oval and have a thick shell presenting numerous depressions; the shell itself is brownish, but it is colourless at the somewhat thickened poles; it measures 60µ in length by 40µ in breadth. The larva measures 240µ by 14µ.
Dioctophyme gigas lives in the pelvis of the kidney, more rarely in the abdominal cavity of the seal, otter, dog, wolf, fox, horse, marten and polecat, exceptionally also in human beings. It also occurs in tumours of the mamma and perinÆum. Most of the cases in which this parasite has been reported as occurring in man may be traced back to unrecognized Ascaris lumbricoides or to clots of fibrin; seven certain cases, eight more or less doubtful, however, remain.
The source of infection is unknown, but according to Balbiani the eggs develop an embryo in water or moist soil, and this embryo may remain alive several years without hatching; the infection of dogs with embryo-containing eggs did not succeed; an intermediate stage in fishes is conjectured, but still the infection of cattle and horses is unintelligible.
Family. StrongylidÆ.
Sub-family. MetastrongylinÆ, Leiper, 1908.
Buccal capsule absent or slightly developed, vagina elongate, uteri convergent307 and have a simple musculature. Parasitic in the respiratory or circulatory system. Genera: Metastrongylus, Synthetocaulus.
Genus. Metastrongylus, Molin, 1861.
Mouth with six lips, of which the two lateral are the largest. Postero- and postero-external rays308 of bursa thin, the rest thick. Only the median ray double. Spicules very long and slender, striated. Vulva immediately in front of anus. Eggs contain an embryo when laid.
Metastrongylus apri, Gmelin, 1789.
Syn.: Gordius pulmonalis apri, Ebel, 1777; Ascaris apri, Gmelin, 1789; Strongylus suis, Rud., 1809; Strongylus paradoxus, Mehlis, 1831; Strongylus elongatus, Duj., 1845; Strongylus longevaginatus, Dies., 1851.
The male measures 12 to 25mm. in length; the bursa is bilobed; there are five rays in each lobe; the spicules are thin and up to 4mm. in length. The females measure 20 to 50mm. in length, the anus is close in front of the posterior extremity, which
Fig. 308.—Metastrongylus apri: one side of bursa. a., anterior; a.e., antero-external; a.m., antero-median; p.m., postero-median; p.e., postero-external; p., one division of posterior ray. (Stephens.)
Metastrongylus apri frequently lives in the bronchial tubes—usually the smaller ones—of the pig309 and wild boar; it is also found occasionally in sheep and in man; in young pigs it is apt to set up a bronchitis, which frequently causes death.
The first communication as to the occurrence of this species in man was that of Diesing, who, in 1845, in Klausenburg, had the opportunity of examining StrongylidÆ found by Jortsits in the lung of a little boy, aged 6, in Transylvania; probably also the Nematodes found in the trachea and larynx of man, and described by Rainey and Bristowe as specimens of Filaria trachealis, belong to this group; according to Chatin, Metastrongylus apri may also occur in the intestine of man; this occurrence, however, may in all probability have been due to an accidental introduction of adult worms into the intestine, and should not be attributed to an infection by the larval stage.
No experiments to induce infection have been made; it is probable, however, that infection is direct and without the aid of an intermediate host.
Sub-family. TrichostrongylinÆ, Leiper, 1908.
StrongylidÆ with buccal capsule absent or slightly developed, vagina short, uteri divergent (i.e., anterior and posterior), ovejectors differentiated. Parasitic in the alimentary canal. Contains the genera Trichostrongylus, HÆmonchus, Ostertagia, Nematodirus, Cooperia, Dictyocaulus.310
Genus. Trichostrongylus, Looss, 1905.
Very small StrongylidÆ. Mouth with three small lips and nodular or punctiform papillÆ. Cervical papillÆ absent. Bursa entirely closed, with large lateral lobes, and median lobe not distinctly defined. Anterior311 rays double, the branches widely divergent, one thin, the other thick, and close to the antero-median. The postero-median ray is thin and close to the postero-external. Posterior ray bifurcate, each branch bifid at the tip (fig.311). Spicules short, spoon or spatula-like, with on the broad anterior end a lateral knob or disc and in front of the point an angular projection. Gubernaculum of a peculiar canoe or shoe shape in profile. Vulva in the hinder half of the body. Tail with two minute papillÆ just in front of tip. Eggs thin shelled; when laid they show eight to thirty-two segments. Parasitic in duodenum, seldom in the stomach of herbivora.
Fig. 309.—Trichostrongylus instabilis: left, posterior end of male; right, spicule and gubernaculum, side view. Cf. fig.311. Magnified. (After Looss.)
Fig. 310.—Trichostrongylus instabilis: posterior end of female. Magnified. (After Looss.)
Trichostrongylus instabilis,312 Railliet, 1893.
Syn.: Strongylus instabilis, Railliet, 1893; Strongylus subtilis, Looss, 1895.
Male 4 to 5·5mm. long, 0·08mm. thick in front of bursa. Spicule 0·135 to 0·145mm. long, accessory piece (gubernaculum) 0·07mm. thick. Antero-external ray usually thickest of all, occasionally only as thick as the antero-median; postero-median far more slender than the antero-external and antero-median and nearer to the postero-external than to the antero-median. Female 5 to 6mm. long, vulva 1·05 to 1·2mm. distant from the tip of the
This species lives in the duodenum, exceptionally also in the stomach of Ovis aries, O. laticauda, Antilope dorcas, Camelus dromedarius (Egypt), Cynocephalus hamadryas (North Africa), sheep and goats (France), and has been found by Looss in bodies of fellaheen at Alexandria and in the stomach of a Japanese female by Ijima.
Trichostrongylus probolurus, Railliet, 1896.
Syn.: Strongylus probolurus, Railliet, 1896.
Male 4·5 to 5·5mm. long, in front of bursa 0·08mm. thick; spicule 0·126 to 0·134mm. long, gubernaculum 0·075 to 0·08mm. long. Bursa: latero-anterior rib thickest; antero-external thicker than antero-median, postero-median and postero-external very short and close together. Female 4·5 to 6mm. long, vulval opening 1·08 to 1·25mm. from tip of tail, placed longitudinally, and slightly curved, 76µ long, always longer than the unpaired portion of the ovejector; anus 0·040 to 0·05mm. distant from tip of tail. Posterior end thick, point of tail short. Ova 76µ to 80µ by 43µ to 46µ.
Fig. 311.—Trichostrongylus probolurus: tail of male from left side. d., posterior; e.d., postero-external; p.l., postero-median; m.l., antero-median; e.l., antero-external; l.v., latero-anterior; v.v., antero-anterior; gub., portion of gubernaculum; sp., portion of spicules. × c. 300. (After Looss.)
Fig. 312.—Trichostrongylus probolurus: spicules and gubernaculum of male; on left, ventral view; on right, lateral view. × c. 300. (After Looss.)
Habitat.—In the duodenum of Ovis aries, O. laticauda, Antilope dorcas, Camelus dromedarius (Egypt) and occasionally also in man (Egypt).
Trichostrongylus vitrinus, Looss, 1905.
Male 4 to 5·5mm. long, in front of bursa 0·085mm. thick. Bursa larger than in the other two species, antero-external rib thickest,
In duodenum of Ovis aries, O. laticauda, occasionally in Camelus dromedarius and in man (Egypt).
Fig. 313.—Trichostrongylus vitrinus: tail of male from left side. d., posterior; e.d., postero-external; p.l., postero-median; m.l., antero-median; e.l., antero-external; l.v., latero-anterior; v.v., antero-anterior; gub., portion of gubernaculum; sp., portion of spicule. × c. 300. (After Looss.)
Fig. 314.—Trichostrongylus vitrinus: spicules and gubernaculum; on left, ventral view; on right, lateral view. × c. 300. (After Looss.)
Genus. HÆmonchus, Cobb., 1898.
Fig. 315.—HÆmonchus contortus: vulval region of female viewed from left side. int., intestine; lab., linguiform process covering vulva; ov., ovary; ovij., ovejector; ut., uterus; vag., vagina; vul., vulva. ×75. (After Ransom.)
Small mouth cavity contains a “tooth” or “lancet” arising from the dorsal side. Cuticle of head and neck not inflated. Cervical papillÆ well marked. Bursa bilateral, with large lateral lobes and a small dorsal lobe not median, but lateral, attached to the base of one of the lateral lobes (fig.316). Posterior ray bifurcate, each branch bifid apically. Each lateral lobe six rays. Anterior rays separated distally, curving forward. Antero-median and postero-median rays distally curve away from the antero-external. Postero-external ray long and slender. Spicules less than 1mm. Gubernaculum present. Vulva in posterior part of body covered by a prominent tongue-like flap. Eggs ellipsoidal.
HÆmonchus contortus, Rudolphi, 1803; Cobb., 1898.
Dorsal “tooth” or “lancet” 10µ to 15µ long. Cervical papillÆ 0·3mm. from head.
Male 20mm. long by 400µ thick (maximum). Asymmetrical lobe
Fig. 316.—HÆmonchus contortus: tail of male, dorsal view, d., posterior ray of the asymmetrically placed posterior lobe; e.d., postero-external; p.l., postero-median; m.l., antero-median; e.l., antero-external; l.v., latero-anterior; v.v., antero-anterior; gub., gubernaculum; sp., spicule. ×75. (After Ransom.)
Female 18 to 30mm. by 500µ (maximum). Vulva 3 to 4·5mm. from tip. Linguiform flap 0·5mm. (a second one exists, according to Brumpt). Anus 400µ to 630µ from tip. Tail acutely pointed. Eggs 75µ to 95µ by 40µ to 50µ.
Habitat.—Fourth stomach of cattle, sheep, antelope.
Distribution.—Europe, America, Africa, Asia, Australia, New Zealand. Once in man in South America by de MagalhÃes.
Pathology.—Produces anÆmia, emaciation, dropsy in sheep; and
Life-history.—Rhabditic embryos easily hatch in water, then moult several times, becoming eventually “filariform” larvÆ enclosed in the moulted skin. These crawl up blades of grass and are swallowed by sheep, etc.
Genus. Nematodirus, Ransom, 1907, emend. Railliet, 1912.
Head over 50µ in diameter. Cuticle may be slightly inflated and often transversely striated. Cuticle with eighteen distinct longitudinal ridges. Cervical papillÆ absent (?). Posterior lobe of bursa reduced to short lobules each with a dorsal ray. Antero-anterior + latero-anterior (= anterior double) rays close together, parallel; antero-external ray diverges widely from antero- and postero-median, which are close together and parallel. Postero-external ray slender. Spicules more than 0·5mm. long, at most one-twelfth of body, united by a membrane throughout their length or only distally. Gubernaculum absent. Vulva behind middle of body. Eggs ellipsoidal, shell rather thick.
Habitat.—Duodenum of ruminants.
Sub-genus. Mecistocirrus, Railliet, 1912.
Head slightly inflated, with transverse striations. Skin with eighteen longitudinal ridges, but little apparent; cervical papillÆ distinct. Bursa bilobed; median ray double (= postero-median + antero-median); very large antero-external at the edge, close to the anterior. Spicules very long, slender, one-sixth length of body (3·5mm.); tail pointed. Vulva immediately in front of anus.
Habitat.—Stomach of ruminants.
Mecistocirrus fordi, Daniels, 1908.
Syn.: Strongylus fordi, Daniels, 1908; Strongylus gibsoni, Stephens, 1909; Nematodirus fordi, Leiper, 1911.
Male 21mm. long by 0·4mm. thick. Cervical papillÆ 0·45mm. behind the head. Spicules about 7mm. long, i.e., one-third of the body length. At the level of the postero-external rays of the bursa, the bursa has a projecting lobule.
Fig. 317.—Mecistocirrus fordi: bursa of male, dorsal view. The rays are (1) postero-external, (2) median (= postero-median + antero-median), (3) antero-external, (4) latero-anterior, (5) antero-anterior. These two latter are parallel. The posterior ray is absent. (After Stephens.)
Female 25mm. long. Anus 0·2mm., vulva 0·5mm. from the tip of tail. Eggs 100µ by 53µ.
Sub-family. AncylostominÆ, Railliet, 1909.
StrongylidÆ with buccal capsule, well developed. Uteri divergent. Parasitic in the alimentary canal, exceptionally in the respiratory system.
Group. ŒsophagostomeÆ, Railliet and Henry, 1909.
Bursa with anterior and median ray cleft (not double), postero- and postero-external arising from a common trunk, posterior bifurcated, each limb bidigitate.
Contains at present four genera: (1) Ternidens, (2) Chabertia, (3) Œsophagostomum, (4) Agriostomum.
Genus. Ternidens, Railliet, 1909.
Buccal capsule sub-globular, opening obliquely in the dorsal surface, and having at the bottom three complex teeth resembling those of Triodontophorus.313 Two crowns of leaflets; peristomic collar moderate, edge of bursa slightly toothed.
Type.—T. deminutus, Railliet and Henry.
Ternidens deminutus, Raill. and Henry, 1905.
Syn.: Triodontophorus deminutus, Raill. and Henry, 1905.
Body relatively thick. Cervical papillÆ 0·5mm. behind the head. Buccal capsule 40µ deep. Teeth 40µ long.
Fig. 318.—Ternidens deminutus. A, head end, ventral view: c, crown of leaflets; v.o., buccal cavity; d, pharyngeal plates; ph., pharynx; n., valve. B, lateral view. C, tail of female. D, bursa of male: a., anterior ray; a.e., antero-external; m., median; p.e., postero-external; p., posterior. E, pharyngeal plate. Enlarged. (After Railliet and Henry.)
Male 9·5mm. long by 560µ thick. Œsophagus 660µ long. Bursa broader than long, the lateral lobes united by a small posterior lobe with slightly sinuous margin; edge of bursa finely toothed. Spicules about 900µ long.
Female 12 to 16mm. long by 650µ to 730µ thick. Œsophagus 860µ long. Vulva forms a distinct projection 480µ from tip of tail. Anus 240µ to 270µ from tip. Eggs 60µ to 80µ by 40µ.
Habitat.—Large intestine of a negro (Comoro Islands) and in the natives of Nyasaland and Portuguese East Africa. Also in large intestine of Macacus sinensis and Macacus cynomolgus.
Genus. Œsophagostomum, Molin, 1861.
No teeth. Cuticle around the mouth dilated to form a narrow cuticular “peristomic collar.” Separated by a constriction from this is a much more extensive inflation, the “cephalic vesicle,” bounded abruptly behind on the ventral side by a transverse groove, the “ventral cleft,” which is always present even in absence of the vesicle. Buccal cavity of slight depth with a short dorsal tunnel. Internal margin of the mouth armed with chitinous leaflets (“external crown”); internal border of the buccal capsule armed with short tongue-like leaflets (internal crown). Lateral membranous wings may extend backwards from the ventral cleft. Cervical papillÆ present. Bursa with two lateral lobes united by a smaller median lobe. Spicules over 5mm. long, slender; gubernaculum inconspicuous. Vulva in front of anus. Adults usually in large intestine of ruminants, suidÆ, tapirs, edentates and apes. LarvÆ sometimes in nodules in intestinal wall.
Œsophagostomum brumpti, Railliet and Henry, 1905.
Female immature, 8·5 to 10·2mm. long, 0·295 to 0·325mm. thick. Cuticle transversely striated. The cephalic vesicle immediately behind the vestibulum oris, embracing the anterior two-fifths of the oesophagus, extending ventrally, however, towards its posterior end. Vestibulum oris formed by a cuticular band provided with a crown of twelve apical leaflets directed forward and inwards; six cephalic papillÆ (two lateral, four submedian); buccal capsule in front of cervical swelling not delineated circularly behind, but provided with three wide incisions (one dorsal, two sub-ventral). Œsophagus, 0·470 to 0·500mm. long, two cervical papillÆ at five-eighths of its length. Vulva 0·350 to 0·475mm., anus 0·170 to 0·200mm., before tip of tail.
Habitat.—Found by Brumpt in tumours of the cÆcum and colon of a native of the River Omo (Lake Rudolph), East Africa. Immature forms only were present. Adults have been found in similar tumours in monkeys.
Fig. 319.—Œsophagostomum stephanostomum var. thomasi. 1, male, natural size; 2, female, natural size; 3, head of female, ventral view, showing cephalic vesicle and ventral cleft limiting it behind, ×55; 4, head of female, dorsal view, ×225; 5, head of male, end view, showing external and internal leaf crowns, ×225; 6, tail of male, lateral view (cf. fig.318, D), ×20; 7, tail of female, lateral view, ×20; 8, Œs. thomasi, posterior ray of bursa, ×150; 9, Œs. dentigerum, from chimpanzee, posterior ray of bursa, ×150; 10, Œs. stephanostomum, from gorilla, posterior ray of bursa, ×150.
Pathology.—They occur in hÆmorrhagic cysts in the submucosa or
Fig. 320.—Œsophagostomum stephanostomum var. thomasi: cÆcum and ascending colon. Subperitoneal cysts are seen on the top right hand, and in the lumen of the gut numerous cysts arranged transversely. The small roundish patches are areas of necrosis in the cyst walls. (After Thomas.)
Œsophagostomum stephanostomum var. thomasi, Raill. and Henry, 1909.
Body thick, pointed only at the ends. Buccal capsule much reduced. External crown of thirty-eight leaflets (the “crown” nearest the centre of fig.319, 5). Male 17 to 22mm. long by 750µ thick. Spicule 1·380 to 1·475mm., slightly curved at the tip. Female,
Œs. stephanostomum, Stossich, 1904, in the large intestine of gorilla. Œs. stephanostomum var. dentigera, Raill. and Henry, 1909, in the chimpanzee.
Habitat.—In large and small intestine of man, Brazil.
Pathology.—Nodules occur in the gut wall; 187 were found by Thomas in his, the sole case. The tumours contain each a single worm.
Fig. 321.—Œsophagostomum stephanostomum var. thomasi: portion of the ileum, showing a cyst with protruding worm. ×8. (After Thomas.)
Fig. 322.—Œsophagostomum stephanostomum var. thomasi: colon with oesophagostome withdrawn from its cyst cavity. ×20. (After Thomas.)
Œsophagostomum apiostomum, Willach, 1891.
According to Leiper, Œs. brumpti is identical with, and hence a synonym of, this species. Parasitic in large intestines of monkeys, producing dysentery, and in man (Northern Nigeria).
According to Walker this species is common in Philippine monkeys. Ova are scanty in the fÆces. They measure 73µ to 84µ by 44µ to 57µ and are in the morula stage. They are easily cultivated. The rhabditiform larva is 340µ by 16µ and has a long filiform tail. It moults twice, and at the second moult becomes a filariform larva retaining the skin of this moult, this stage being that of the mature larva. It now measures 9mm. long by 30µ thick. Walker suggests that the mode of infection is similar to that of ancylostomes.
Group. AncylostomeÆ, Railliet and Henry, 1909.
Bursa with anterior ray cleft, median double,314 postero- and postero-external arising from a common trunk, posterior bifurcate, each limb being tridigitate. Vulva in posterior third of body. Uteri divergent.
Contains the following genera: (1) Strongylus,315 (2) Ancylostoma, (3) Uncinaria, (4) Characostomum, etc.
Genus. Ancylostoma, Dubini, 1843, emend. Looss, 1905.
Ventral margin of mouth capsule armed with teeth, the “roots” of which are continued backwards and appear on the external surface of capsule as rib-like thickenings. Terminal third of dorsal ray cleft. Genital tubes very long, with short, closely packed diagonal convolutions.
Ancylostoma duodenale, Dubini, 1843.
Fig. 323.—Ancylostoma duodenale, male. B, bursa; Bm, bursal muscles; Cdr, cement gland surrounding the ejaculatory duct; Glc, cervical glands; N, nucleus of cephalic gland; Nr, nerve ring; T, testes; Sp, spicule; Vs, vesicula seminalis. ×15. (After Looss.)
Buccal Capsule.—The buccal capsule is bent dorsally, 0·21mm. long, 0·19mm. broad. If a worm is rolled under the cover-glass so that the dorsal side is upwards, we observe the following features (fig.325): In the dorsal edge of the chitinous capsule there is a gap as if a U-piece had been punched out. This is the “dorsal gap or incision.” The so-called “dorsal teeth” are simply the rounded edges of the tips of this gap. They project beyond the skin which covers the capsule externally. Below this gap is seen a curved line which, if followed along the sides of the capsule on each side, merges into the base of the most posterior ventral tooth. This line is the optical expression of a very shallow groove on the inside of the capsule. The skin on the outside of the capsule, which is reflected over the edge of and into the capsule, dips into this groove, which gives it a firm attachment. Below the middle (dorsally) of this curved line there is a thickening in the capsule wall, which is perforated by the opening of the dorsal oesophageal gland. This is the “dorsal ridge”; in optical section it has a conical appearance with a lumen (of the duct).
Fig. 324.—Ancylostoma duodenale, female. A, anus; Gcph, cephalic gland; N, nucleus of cephalic gland; Glc, cervical gland; Ov, ovary; Pex, excretory pore; Rs, receptaculum seminis; Ut, uterus; V, vagina. ×15. (After Looss.)
Male 9mm. long by 0·45mm. thick, female 12mm. long by 0·6mm. thick. Pale flesh colour, or an intense red in posterior third. Anteriorly may be more or less black due to (blood) pigment in the cells of the chyle intestine (= stomach + small intestine). The worm is about the same thickness all through and is plump and rigid. Cuticle striated. The body has a marked torsion, so that if the ventral side of the head is upwards the anus appears to open laterally and vice versÂ. The dorsal curve of the head end is only slight and the oesophagus is roughly cylindrical.
On the ventral wall one sees the two pairs of strong teeth, their points being directed somewhat backwards. They are covered by cuticle above and below, but their points are free, piercing the cuticle. The “roots” of these teeth followed backwards appear as two thickenings or ribs on the outside of the capsule wall, so that the outside wall is not smooth—a characteristic of the genus Ancylostoma. In the space between these ribs lies the ventral nerve papilla,
Cervical PapillÆ.—Two, one on each side behind the head at the level of the excretory pore. They consist of “pulp,” i.e., extensions of the substance of the lateral bands covered by cuticle and supplied with a nerve (fig.326).
Fig. 325.—Ancylostoma duodenale: showing ventral teeth, dorsal cleft, and behind it the dorsal ridge with duct of dorsal oesophageal gland. × c. 200. (After Looss.)
Œsophageal Glands (3).—The chitin of the triradiate oesophagus is continuous with that of the buccal capsule. In its muscular walls are three glands—one dorsal, two sub-ventral. The dorsal gland opens into the buccal cavity through the dorsal ridge; the two others into the lumen of the oesophagus at the nerve ring. They branch freely amidst the muscles. They are probably digestive in function.
Cephalic Glands (2).—Lie in the lateral lines or bands on either side. They begin about the middle line of the body, and their ducts open at the base of the outer ventral tooth on the surface of the skin on each side. Each is 0·15mm. thick in the middle, and has a single nucleus about as big as an ancylostome egg (N, fig.323). They probably function as poison glands.
Excretory System and Cervical Glands (2).—The excretory pore lies in the mid line ventrally behind the oesophageal nerve ring (figs.324 and 326). It opens into the excretory vesicle, a cavity in a large cell with lateral appendages which fuse with the lateral lines, this cell thus forming the “bridge” of the excretory system. Adhering to this (bridge) cell are the spindle-shaped cervical glands (Glc, fig.324), and branches from the excretory vesicle enter the glands, which are excretory in function; the vesicle also receives branches
Fig. 326.—Ancylostoma duodenale: diagrammatic representation of excretory system. ex.p., excretory pore; e.c.g., excretory cervical gland; Ex. ves., excretory vesicle in B.c., bridge cell, which is connected with c.g., cervical gland, and l.l., lateral lines; ceph.g., cephalic gland; l.ex.c., lateral excretory canal passing into the bridge cell; l.l., lateral line containing excretory canal and cephalic gland; c.p., cervical papilla; n., nuclei of bridge cell. (After a drawing of Looss.)
Lateral Lines.—(1) Are broad elevations of the subcuticle, in which, here and there, a nucleus occurs. (2) Near the bursa in the male they increase in volume, and finally divide into branches which form the “pulp” of the different rays. (3) In addition to the lateral lines or bands, there is also a dorsal and ventral band. (4) The ventral band is well developed caudally, forming a large pad dorsal to the cloaca, “pulvillus post-analis.”
The bursal rays are outgrowths of the lateral lines. Beside this “pulp” they contain a nerve, and at their bases complex muscles.
The Bursa is closed on all sides with a short median (ventral) lobe, which may be tucked inwards. It is an outgrowth of the inner layer of the skin pushing the outer layer before it, so that it consists of three layers, not four, as it would be if it were a fold. The bursa is twice as broad as long. It is supported by a variety of rays, the arrangement of which is best followed from the figure (fig.327). The
In the male there are prebursal papillÆ and minute caudal papillÆ in the female.
In the female the inner layer of the cuticle projects at the posterior end as a sharp spike, 20µ long, which may sometimes be broken off.
Fig. 327.—Ancylostoma duodenale: bursa enlarged. Ca, anterior ray cleft; cle, antero-external; cls, antero-median; clp, postero-median; Cde, postero external; Cd, posterior bifurcated, each bifurcation tridigitate. (After Railliet.)
Ovaries.—The anterior tube runs from the cephalic to the posterior end and back again. The posterior tube begins anteriorly, runs to the posterior end of the body, and then back to the cephalic end, forming a vulval loop before ending. The ovaries on the whole run in oblique coils. The uterus is the thicker portion of the tube, 5mm. long. A short tube connecting the ovary and uterus is the oviduct. The two uteri unite to form a single duct, the vagina, opening 1mm. behind the middle line. The portion of the uterus next to the oviduct functions as a seminal receptacle, whereas the part next the vagina functions as an ovejector.
Testis.—The blind end begins a little behind the beginning of the cement gland. The transverse coils occupy the middle third of the body. About the middle of the body it passes into the spindle-shaped seminal vesicle, which, with the spicular canal and rectum, opens into the cloaca. An anterior longitudinal coil pushing in between the cervical glands is characteristic of Ancylostoma. The cement gland surrounds the ejaculatory duct for practically its whole course, and it occupies nearly the posterior half of the body and
Spicules are 2mm. long, ending in a fine point. They are moved by exsertor and retractor muscles. At first they lie free in the body cavity; next in a groove in the dorsal wall of the cloaca; then in an isolated canal, and finally in two canals. Anteriorly each has two longitudinal crests on its inner surface. These meet the corresponding crests of the other spicule, and so form a canal along which the sperm passes into the female. The gubernaculum is a thickening of the dorsal wall of the cloaca. It is not a free piece, but is moved by various muscles.
Fig. 328.—Ancylostoma duodenale: bursa of male. The rays from left to right are: (1) anterior cleft; (2) antero-external; (3) and (4) median doubled, i.e., antero-median and postero-median; (5) postero-external arising from a common trunk with the posterior. × c. 120. (After Looss.)
Genital Cone is a prominence on the floor of the bursa on the ventral side of the body, on which the genito-anal orifice opens. The cone is only slightly marked in Ancylostoma duodenale, but is much more prominent in Necator americanus.
Distribution.—Africa, Egypt, Europe, Japan, China (mainly), but in association with Necator americanus in Southern States of America, British India, Assam, Burma, Hongkong, Liberia, Jamaica, Martinique, Costa Rica, Colombia, Antigua, Guadeloupe.
Habitat.—The worms live in the jejunum, less frequently in the duodenum, of man only.
Food.—The worms feed on the mucous membrane of the gut, attaching themselves to the base of the villi, sucking these in; and when these are destroyed they attack further the submucosa. As a rule the worms have no blood in the gut, but in their attack on the submucosa a blood-vessel may be eroded, and so the gut of the worm filled with blood.
Development.—The eggs are oval with broadly rounded poles, 56µ to 61µ by 34µ to 38µ. In fresh fÆces they contain four granular nucleated segmentation masses of the ovum (fig.329) separated by a clear space from the shell.
Fig. 329.—Ancylostoma duodenale: eggs in different stages of development. a to c, in fresh fÆces; d, containing a larva, only in old fÆces. ×336. (After Looss.)
Egg of Ancylostome appears to have a single contour. Under high powers this appears double, but they are the outer and inner surface of the true (chitinous) egg-shell. Internal to this is the extremely delicate yolk-envelope, a kind of skin secreted by the egg cell around itself for protection. The function of this is probably to absorb water to swell and burst the outer chitinous shell. The embryos when hatched are termed larvÆ.
Embryos which are ready to hatch have their bodies almost free from granules; others, though apparently mature, that have granules will not hatch.318
Fig. 330.—Ancylostoma duodenale larva on fourth day of culture on right; Strongyloides stercoralis larva on left. (After Leichtenstern.)
Larva.—Stage I: Average length, 25mm. Maximum thickness in oesophageal region, 17µ. Head end fairly blunt, from behind the anus (the tail) tapering in an uniform manner. Buccal cavity is characteristic, 10µ to 12µ by 1µ to 8µ, longer and narrower than the corresponding larvÆ of Strongyloides stercoralis. Œsophagus “rhabditic” in character, i.e., it has three sections, but they are not so clearly marked off as in larvÆ of the genus Rhabditis. The posterior bulb has a Y-shaped valve, the function of which, according to Looss, is to prevent regurgitation of food. The granules of the gut serve as a reserve of food, and are used up if the larvÆ are starved. The genital rudiment consists of two cells half-way between the end of the
Stage II: The larva is now in this stage, which does not differ much from the previous one. It grows to 0·5mm. The mouth opening closes. The oesophagus elongates, becoming cylindrical or “filariform”; a new skin is formed underneath the old one, and in about a week moult II takes place.
Stage III: The mature larva remains enclosed in the old skin. Its movements are now much more active and of a boring character. Length is now 0·6mm. This mature stage has been erroneously called the encysted larva, because there is no cyst secreted from its
Fig. 331.—Ancylostoma duodenale: left, four days after transmission into dog, 190/1; in the centre, at the commencement of the second stage of development (five to six days), 105/1; on the right, fourteen to fifteen days after transmission. 42/1. (After Looss.)
Bionomics of Development.—Air: Eggs can develop when shut off from the air for a “comparatively long” time.
Temperature: Hatching takes from eight hours upwards. Eggs develop best at 25° to 30°C., but will not develop below 8° to 10°C. The larvÆ, however, will stand freezing.
Moisture: Eggs and larvÆ do not live long under water, because they suffocate or starve, but mature larvÆ will live for months (six to twelve) in water; they require no food—in fact, can take none in—but live on their reserve granules, and in course of time become as clear as glass.
Thigmotropism: The mature larvÆ, after casting their skin, will penetrate pith, climb up stems, stalks, etc., and creep into any pore.
It is important to recognize that this third stage of the mature larva is the only infective one.
Mode of Entry into the Body.—Infection is effected through the mouth (Leichtenstern and others), and also through the skin, as was first discovered by Looss and afterwards confirmed from the most diverse quarters, partly in the case of Ancylostoma duodenale, partly in that of A. caninum in dog, man, and monkey. The larvÆ that gain access to the intestine partly through contaminated food, or through unwashed hands, or under some circumstances through water, first throw off their “sheath”—that is, they complete moult II. Moult III takes place four to five days after they have reached the gut, and they now have a mouth capsule supplied with four small teeth arranged crosswise, enabling them to fasten on to the intestinal epithelium, upon which they feed. On this food the worms grow in four to six days to 3 to 5mm. in length, and now moult IV. takes place, thus attaining their definite shape and distinctive character. About eight days later the sexual organs commence to function; at this time the first copulation should be taking place—it will later be frequently repeated—and a few days later the first ova are laid, first in less and later in larger numbers, so that they appear in the fÆces about four to five weeks after the infection.320
Infection by the Skin.—Mature larvÆ, which are placed on the skin of man or suitable animals, cast their “sheath” and bore their way through delicate fissures either horizontal in the superficial scales of the epidermis, or through vertical fissures into hair follicles where these exist, and then they invade the cutis. Now according as they migrate further into the lymphatic vessels or the small vesicles, the final path to the gut differs to some extent. The blood path leads to the right heart, and from there into the lungs; here the larvÆ leave the blood stream and enter the air passages, over the mucosa of which they travel further headwards, through the bronchi into the trachea and larynx, and from hence through the oesophagus to the stomach; in some cases also they are swallowed. The
The penetration of the skin by the larvÆ also in man causes reddening and burning at the affected points, and this is followed in a few days by transitory swelling in the subcutaneous connective tissue. Skin affections can also be set up by such Ancylostoma (and Strongyloides) larvÆ as do not gain access to the blood or lymphatic vessels or gut; such larvÆ apparently wander further in the connective tissue, and, as Looss has in his own person observed, gain access to the cutis at different points, thus causing progressive swellings (accompanied by intense itching), which cease when the worm again penetrates into the deep tissues. Skin affections such as “ground-itch” or “pani-ghao” occurring in the tropics and only attacking the feet, or other affections (e.g., sump bunches) are now well recognized as being due to the invasion of Ancylostoma larvÆ.
Other names for these skin affections are water-sore, sore feet of coolies, maza-morra, bunches, botches, quaddeln, krÄtze, ampoules, gourmes, taons, pitirr. Whether oral or dermal infection is the more important one further observation must decide.
The duration of life of Ancylostoma duodenale, which is a specific parasite of man and has not been observed in other mammals, amounts to about five years, as strayed larvÆ according to Looss wander for this extent of time in the body.
Cultivation of LarvÆ.—(1) Mix the fÆces (free from drugs such as salines or thymol) with animal charcoal, adding water if necessary till a consistence of porridge is obtained. If the stools are very fluid, allow to sediment first and pour off the fluid. The best charcoal is that made from bones, and should not have an acid reaction. Charcoal is necessary in order to prevent fermentation, which kills the larvÆ. Spread in layers 2 to 3mm. thick in Petri dishes. Incubate at room temperature. To extract the larvÆ from the culture allow the surface thoroughly to dry, then pour on water; the larvÆ wander out and are poured off and subsequently further purified by sedimentation or filtering through blotting paper, the larvÆ passing through.
(2) A funnel is plugged with cotton wool, then filled with washed sand to within a centimetre or two of the rim. Stand this in a jar of water so that the level of the water is slightly below that of the sand. On the surface of the wet sand now place layers of blotting paper, and spread the fÆces, diluted if necessary, on this in layers of a few millimetres thick (vide p.474).
Detection of Eggs.—Vide p.473.
Dermal Infection of Dogs.—Infection with larvÆ of A. caninum. In two hours most of the larvÆ are free in the cutis and in four hours in the subcutaneous tissue. By scraping a few days later the mucosa of the trachea large numbers of larvÆ are found there.
Ancylostoma ceylanicum, Looss, 1911.
Fig. 332.—Ancylostoma ceylanicum: head end, two teeth on each side, the inner almost concealed by the outer. × c. 200. (After Looss.)
At the anterior edge of mouth capsule one large tooth; below or behind this towards the middle line a very small tooth, the tip only of which is seen. Male 5mm. average. Lobes of bursa almost as long as broad, strongly projecting towards the ventral side. Rays short and relatively thick. Female 7mm.
Habitat.—Intestine civet cat (Viverricula malacensis), Ceylon, and man in Bengal according to Clayton-Lane.
Other species are: A. caninum (Ercolani), in cat and dog, Europe and Africa; A. malayanum (Alessandrini), 1905, in the Malay bear (Helaretos malayanus); A. pluridentatum (Alessandrini), 1905, in Felis mitis, Brazil.
Ancylostoma braziliense, Gomez de Faria, 1910.
In cats (and dog), Brazil. Female 8·5mm., male 7·5mm. long. Eggs 65µ by 32µ. Leiper considers it to be identical with A. ceylanicum.
Fig. 333.—Ancylostoma braziliense: bursa of male. (After Gomez de Faria.)
Group. BunostomeÆ, Railliet and Henry, 1909.
Bursa with median double, postero- and postero-external arising from a common trunk, posterior bifurcated, each limb bidigitate (fig.336). Vulva in middle of body or a little in front. Uteri divergent.
Contains the following genera: (1) Bunostomum (= Monodontus); (2) Necator; (3) Bathmostomum; (4) Gaigeria.
Genus. Necator, Stiles, 1903.
Mouth capsule small, narrowed anteriorly (ventrally) by chitinous plates, as in Uncinaria. On each side of the base of the dorsal cone a lateral chitinous plate or lancet with smooth edge (not serrated), ventral lancets as in Ancylostoma. No ridges on outside of ventral wall. Aperture of dorsal oesophageal gland on tip of a cone projecting freely into the buccal capsule. Bursa closed. Posterior ray cleft to its root.
Necator americanus, Stiles, 1902.
Syn.: N. africanus, Harrison, 1910.
Fig. 334.—Necator americanus. Showing cutting plates and the projecting dorsal ridge, and deep in the cavity the edges of the ventral lancets. × c. 475. (After Looss.)
Male 8mm. long, female 10mm. The head is strongly bent dorsalwards so that almost by this character alone it can be distinguished from Ancylostoma duodenale. The buccal capsule is markedly small—in the male, 0·093 by 0·084mm., in the female 0·11 by 0·097mm. There are no teeth anteriorly on the ventral side of the capsule, but instead there are two cutting chitinous plates, the anterior portions of which are prominent and angular, and meet in the middle line in front. Posteriorly on each side the plate projects less, while between the anterior and posterior parts there is a deep angle. The inner (posterior) ventral lancets which also occur in A. duodenale are large, and project far into the lumen, the tips of these, of the lateral lancets, and of the dorsal cone almost meeting in the centre of the lumen. As already stated in the definition of the genus Necator, there are also lateral lancets which start from the base of the dorsal cone. This dorsal ridge, or rather in this case cone, is a striking object in
Fig. 335.—Necator americanus: lateral view, showing the dorsal ridge perforated by the duct of the dorsal oesophageal gland, the lateral lancet and ventral lancet and the nerve papillÆ. × c. 475. (After Looss.)
The bursa is about as long as broad, but has the lateral lobes strikingly lengthened, giving a trilobed appearance (fig.336), but as in Ancylostoma duodenale it is closed on the ventral side. The distribution of the rays is best understood from the figure. The genital aperture lies on a marked conical protuberance; the cement gland is bilobed in transverse section. In the female the opening of the vulva is in front of the middle line, in A. duodenale it is behind.
The spicules, 0·92mm. long are hooked at the extremity.
Fig. 336.—Necator americanus: bursa of male. The rays from right (top) to left are: (1) posterior, (2) postero-external, (3) and (4) median doubled, i.e., postero-median and antero-median, (5) antero-external, (6) anterior (cleft), and above it on left a pre-bursal ray. × c. 120. (After Looss.)
Eggs more pointed at the poles than those of A. duodenale, 64µ to 72µ by 36µ, so that it may not be possible to distinguish single eggs owing to individual variations, yet on comparing a number they can be distinguished.
Geographical Distribution.—Brazil, Porto Rico, Cuba, Central Africa, East Africa, Victoria Nyanza, Gold Coast, Uganda, North-Western Rhodesia, Ceylon, Mysore. For other localities where A. duodenale is also found see p.450.
Habitat.—In small intestine of man and gorilla (Troglodytes gorilla).
Necator exilidens, Cummins, 1912.
Syn.: N. africanus, Looss, 1911.
Male 7mm., female 9mm. long. The edges of the cutting plates are rounded, not angular, and do not meet in the middle line. Inner (posterior) ventral lancets very small. Lateral lobes of bursa broader than long. Rays thick and plump.
Habitat.—In the chimpanzee (Anthropopithecus troglodytes).
Ancylostomiasis.
Morbid Anatomy.—Organs pale and bloodless. Abdominal organs sodden, and there is fluid in the serous cavities. Lungs: oedema. Kidneys: fatty changes, especially large pale kidney. Liver and heart also show fatty changes—there is much hÆmosiderin in the liver cells. Blood: early stages, a leucocytosis 20,000 upwards, and eosinophilia 50 per cent. Later, anÆmia (hydrÆmia). The number of worms found varies from ten to 1,000. They are rare in the duodenum, but occur as far as 6ft. from the pylorus.
Group. SyngameÆ, Railliet and Henry, 1909.
Bursa with anterior and median ray cleft; antero-external, close to median; postero-external, arising separately from posterior; posterior bifurcate to base, each branch bifurcate or trifurcate. Vulva in the anterior fourth of body. Uteri divergent.
Genus. Syngamus, von Siebold, 1836.
Head thickened, not tapering; broad mouth with gaping buccal capsule.
Male and female often in permanent copulÂ.
Parasitic in respiratory passages of birds and mammals.
Habitat.—S. trachealis in poultry; S. bronchialis in goose; S. laryngeus in cattle; S. vasicola in goats, etc.
Syngamus kingi, Leiper, 1913.
Buccal capsules of male and female on same level. In S. trachealis and S. laryngeus, that of male in front of that of female. In S. dispar, that of male behind that of female. Œsophagus of male one-sixth, that of female one-ninth of total length. Mouth capsule in male and female terminal; it is dorsal in S. trachealis and in mammalian
Habitat.—Found in sputum of patient by King in St. Lucia. Normal host probably a carnivore.
Fig. 337.—Syngamus kingi: anterior end of male. (After Leiper.)
Fig. 338.—Syngamus kingi: anterior end of female. (After Leiper.)
Family. PhysalopteridÆ.
Genus. Physaloptera, Rudolphi, 1819.
Mouth surrounded by two large lateral lips bounded posteriorly by a cuticular band projecting anteriorly, forming a collar. Each lip bears anteriorly and inwardly a cuticular appendage, the external tooth. Immediately below and internal to the external teeth the internal teeth, one on each lip. Each lip bears two large submedian papillÆ. Tail of male with four pairs of pedunculated papillÆ in a row on each side external to the six pairs of unpedunculated papillÆ. Spicules unequal. Vulva in the anterior region of the body. Eggs with a characteristic thick smooth shell.
Parasitic in the intestine, more especially the stomach, of mammals (twenty species), birds (twelve species), reptiles (fourteen species).
Physaloptera caucasica, v. Linstow, 1902.
The male measures 14·2mm. in length and 0·71mm. in breadth; the bursa is broad, rounded off in front and narrower at the back; the right spicule measures 0·62mm. in length, the left spicule 1·76mm.; there are two papillÆ in front of the orifice of the cloaca, four behind it and six unpedunculated on the tail. The female measures 27mm. in length, 1·14mm. in breadth; the caudal extremity is rounded off; the vulva is on the border of the first and second sixth of the length of the body; the eggs have thick shells, and measure 57µ by 39µ. It has hitherto only been observed once, by MÉnÉtriÉs in the intestine of man (Caucasus).
Fig. 339.—Bursa of Syngamus trachealis. a., anterior ray cleft; a.e., antero-external; m.a., antero-median; m.l., postero-median; p.e., postero-external; p., one branch of posterior (trifurcate). (Stephens.)
Physaloptera mordens, Leiper, 1907.
Large worms resembling an immature Ascaris lumbricoides.
The inner lancet-shaped teeth have a sharp cutting edge towards the lumen. Below each is a cuticular boss projecting into the mouth (fig.340).
Male 30 to 50mm., bursa with four pairs of pedunculated papillÆ, the second and third lying external to the first and fourth on each side. Spicules unequal, one slender (4·6mm.), the other stouter (6mm.).
Female 40 to 55mm. Tail sharp. Vulva opens between the anterior fourth and fifth of the body. Eggs 43·6µ by 35·3µ with a thick smooth shell.
Habitat.—Œsophagus, stomach, small intestine of man (several cases). Nyasaland and Portuguese East Africa.
Family. AscaridÆ, Cobbold, 1864.
Sub-family. AscarinÆ.
Without oesophageal or intestinal diverticula; spicules without flanges.
Genus. Ascaris, L., 1758.
Intermediate lips and auricles absent. Lips edged with fine teeth. Lips triangular in cross section. Not grooved on internal surface.
Fig. 340.—Physaloptera mordens, Leiper, 1907. (1) adult male: o.e., oesophagus; ch.i., chyle intestine; t.c., testicular coils; ves. sem., vesicula seminalis; sp. 1, long spicule; sp. 2, short spicule; B., bursa. (2) Mouth parts: c., cuticular collar embracing the two lips posteriorly; c.b., cuticular bosses guarding the mouth laterally; e.d., external tooth; i.d., internal tooth; sm.p., submedian papillÆ. (3) egg of P. caucasica. (4) egg of P. mordens. (5) bursa enlarged: ped.p., pedunculated papillÆ; ses.p., sessile papillÆ. (After Leiper.)
Ascaris lumbricoides, L., 1758.
The colouring, in the fresh condition, is reddish-yellow or greyish-yellow; the body is of an elongated spindle shape. The oral papillÆ are finely toothed. The dorsal papilla carries two sensory papillÆ, the two ventral papillÆ each one sensory papilla. The male measures from 15 to 17 to 25cm. in length, and about 3mm. in diameter; the posterior extremity is conical and bent hook-like ventrally; the spicules measure 2mm. in length, are curved, and somewhat broadened at their free end; on each side around the orifice of the cloaca there are seventy to seventy-five papillÆ, of which seven pairs are post-anal. The testicular tube is much folded, showing through the body integument, and is about eight times the length of the body. The female measures 20 to 25 to 40cm. in length and about 5mm. in diameter; the posterior extremity is conical and straight. The vulva is at the junction of the anterior and middle thirds of the body, which, at this point, has a slight ring-like constriction; the convoluted ovaries measure ten times the length of the body.
Fig. 341.—Ascaris lumbricoides. a, posterior extremity of the male with the spicules protruding from the orifice of the cloaca (Sp.); b, anterior extremity from the dorsal surface, the two lobes of the pulp of the lip separated by the “saddle”; c, anterior extremity from the ventral surface; P., excretory pore. (From Claus.)
Fig. 342.—Ovum of Ascaris lumbricoides, with shell and albuminous envelope. 400/1.
The ova are elliptical with a thick (4µ) transparent shell (fig.342) and an external albuminous coating which forms protuberances; the ova measure 50µ to 70µ in length, 40µ to 50µ in breadth; they are deposited before segmentation; the albuminous coating is stained yellow by the colouring matter of the fÆces, but is sometimes absent. The egg cell is unsegmented, it almost completely fills the shell, and its nucleus is concealed by the large amount of coarse yolk granules.
Abnormal or unfertilized eggs also occur in fÆces. They are distinguished by their elongated form (80µ by 45µ), irregularly cylindrical, its contents consisting of refractive granules.
Ascaris lumbricoides is one of the most frequent parasites of man; it is distributed all over the inhabited parts of the world, and though it is particularly frequent in the warmer regions, yet it also occurs
The parasite was known in ancient times; the Greeks called it ????? st???????, Plinius termed it Tinea rotunda, later on it was named Lumbricus teres. The ?s?a??? of the Greeks is our Oxyuris.
The small intestine is the normal habitat of Ascaris lumbricoides; the worms, however, often leave this part of the intestine and wander into the stomach, whence they are frequently evacuated by vomiting, or they may creep through the oesophagus into the pharynx and crawl out through the nose or mouth; very rarely they may find their way into the Eustachian tube or into the naso-lachrymal duct, or into the excretory ducts of the liver and pancreas; exceptionally they may gain the trachea, and they have also been found in the abdominal cavity. They may bore through adhesions between the intestinal wall and the omentum (worm abscess); they occasionally penetrate the urinary apparatus and are passed with the urine; in febrile diseases A. lumbricoides usually leaves the intestine spontaneously. It is obvious that these wanderings may be accompanied by the most serious symptoms, but in sensitive persons the invasion of even only a few intestinal Ascarides gives rise to a series of almost inexplicable symptoms (hysterical, epileptiform attacks, cerebral congestion, aphonia, etc.), which cease with the expulsion of the worms, so that many authors are driven to the conclusion that these Ascarides secrete a toxin. Fortunately, the presence of A. lumbricoides in the intestine is easily demonstrated by the microscopical examination of the fÆces.
Development.—Several authors (Gros, Schubart, Richter, Leuckart and Davaine) have demonstrated that the ova of Ascaris develop in water or moist earth after a long period of incubation. Freezing and desiccation (if not too long) do not injure their powers of development; the duration of the development depends on the degree of the surrounding temperature. At a medium temperature, after a varying period of incubation, it takes from thirty to forty days for the embryo to become formed. The spirally rolled up embryo, with its so-called “tooth,” formed by three papillÆ close together, never leaves the egg-shell in the open, even if the eggs are kept for years under favourable conditions. Davaine proved that the larvÆ hatch out in the intestine of the rat, but are again expelled with the fÆces; he therefore concluded that the hatching likewise takes place within the intestine of man, but is followed by the invasion of the larvÆ. In the meantime Leuckart had sought to infect himself by swallowing embryo-containing eggs, but without results; he
Accordingly, infection occurs partly through water, but principally direct from the soil.
Ascaris, sp.
Wellmann states that yet another species of Ascaris in man occurs in the highlands of Angola: up to the present nothing certain is known about it (Welland, “Critical Notes on Tropical Diseases of the Angola Highlands,” New York Med. Journ. and Philadelphia Med. Journ., August 12 to September 2, 1905.)
Ascaris texana, Smith et Goeth, 1914.
Female alone known; 58 to 60mm. and upwards in length; characterized by the serration of the anterior border of the lip and by the appearance of interlabia. Evacuated by a white settler in Texas. Position of this worm doubtful.
Ascaris maritima, Leuckart, 1876.
Only one immature specimen, a female (43mm. in length and 1mm. in breadth), has hitherto been described, and it was vomited by a child in North Greenland in 1865. (R. Leuckart, “Die menschlichen Parasiten,” 1876, edition 2, i, p.877.)
Genus. Toxascaris (t????, an arrow), Leiper, 1907.
Body anteriorly bent dorsally, cuticle finely striated. Œsophagus without a distinct bulb. Tail of male tapers to a point. Testis in anterior portion of posterior half of body. Vulva about middle of body. Eggs oval and smooth.
Toxascaris limbata, Railliet and Henry, 1911.
Syn.: Lumbricus canis, Werner, 1782; Ascaris teres, Goeze, 1782; Ascaris cati et caniculÆ, Schrank, 1788; Ascaris canis et felis, Gmelin, 1789; Ascaris tricuspidata et felis, Bruguiere, 1791; Ascaris werneri, Rud., 1793; Fusaria mystax, Zeder, 1800; Ascaris marginata et mystax, Rud., 1802; Ascaris alata, Bellingham, 1839.
Striations 6µ to 12µ apart. Cephalic wings long, narrow, semi-lanceolate. Male, 4 to 6cm. Spicules, 1,002µ and 1,005µ. Female, 0·5 to 10cm. Eggs, 75µ to 85µ, shell thick and smooth. Host: dog, occasionally man.
Fig. 343.—Ovum of Toxascaris limbata, with thin albuminous envelope. Magnified.
Fig. 344.—Transverse section through the head part of Belascaris cati from the cat, with the lateral wings. In addition, one may note the four fields of muscles, the longitudinal lines with the oesophagus in the centre. Magnified. (After Leuckart.)
Genus. Belascaris (?????, an arrow), Leiper, 1907.
Body anteriorly bent ventrally, cuticle coarsely striated. Œsophagus with a distinct bulb. Tail of male conical. A papillÆ-bearing protuberance behind the anus. Testis in anterior half of body. Vulva in anterior part of body. Eggs corrugated.
Belascaris cati, Schrank, 1788.
Syn.: Belascaris mystax, Leiper, 1907; Ascaris mystax.
Striations 12µ to 16µ apart. Cephalic wings lanceolate. Male 3 to 6cm. Spicules 17 to 1·9mm. Female 4 to 10cm. Eggs, 65µ to 75µ in diameter, surface finely honeycombed. Host: domestic cat, and man, eight or nine cases.
Belascaris marginata, Rudolphi, 1802.
Striations 16µ to 22µ apart. Cephalic wings long, narrow, semi-lanceolate. Male, 5 to 10cm. Spicules, 750µ and 950µ. Female, 9 to 18cm. Eggs, 75µ to 80µ. Shell finely honeycombed. Host: dog.
Genus. Lagocheilascaris, Leiper, 1909.
Thick lips separated by a furrow from the body; between the lips small intermediate lips without “pulp.” The cutting angle of each lip bifurcated. Along each lateral line a cuticular wing extending the whole length of the body. Eggs, thick shell with a mosaic pattern.
Lagocheilascaris minor, Leiper, 1909.
Male, 9mm., tail sharply curved. Spicules colourless, 3·5 and 4mm. long. More than twenty-four pairs of pre-anal papillÆ, at least five pairs of post-anal. Female, 15mm. Straight posteriorly. Vulva 6mm. from head with two lips. Eggs, 65µ in diameter. Host: man, cutaneous abscesses. Trinidad.
Family. OxyuridÆ.
Genus. Oxyuris, Rudolphi, 1803.
Mouth unarmed. The three labial papillÆ are only slightly protuberant, the oesophagus is long and presents two well-marked bulbs. The vulva is in the anterior part of the body.
Oxyuris vermicularis, LinnÆus, 1767.
Syn.: Ascaris vermicularis, L.; Fusaria, Zeder, 1803.
Fig. 345.—A, male, and B, female, of Oxyuris vermicularis. 5/1.
Colour white, the striated cuticle forms projections at the anterior end which extend some distance back along the middle of the ventral and dorsal surfaces; the longitudinal lateral flanges of the skin corresponding to the lateral lines are well seen in transverse sections; there are three small retractile labial papillÆ around the mouth. The male measures 3 to 5mm. in length, and shortens on death; the posterior extremity of the body is curved ventrally and presents six papillÆ. Spicule 70µ long, hook-like. The female is 10mm. in length and 0·6mm. in diameter; the anus is about 2mm. in front of the tip of the tail; the vulva is in the anterior third of the body; the eggs are oval, asymmetrical, with double-contoured shells, and measure 50µ to 55µ by 16µ to 25µ; they are deposited with clear, non-granular tadpole-like embryos already developed.
Fig. 346.—On the left, female; on the right, male. A, anus; M, mouth; V, vulva. Greatly enlarged. (After Claus.)
Habitat.—Adults in large intestine of man. Young forms in small intestine and often in the appendix.
The worm lives in the lower part of the small intestine, cÆcum and vermiform appendix, and before becoming adult undergoes two or three moults (Heller). According to Wagener the worms at times live in the gut wall, giving rise to calcareous nodules. When the uterus of the fertilized females begins to fill with eggs they leave the cÆcum and travel through the colon to the rectum. The uterus is now packed with eggs which contain a tadpole-shaped embryo. Egg-laying now takes place, partly in the rectum, partly outside, the mode of exit being not only passive through defecation but also an active one on the part of the worms when the patient is in bed. In this case the worms crawl out of the anus, producing a most intolerable itching as they scatter their eggs between the nates and the perinÆum. From here in the case of girls they may get occasionally into the vulva and vagina, and even into the oviducts and so into the body cavity. The worms also may wander through the alimentary canal in the opposite direction, getting out occasionally through the mouth. Recently a rÔle has been assigned to them, as to other gut parasites, in appendicitis and typhlitis.
It is stated that the males die after fertilizing the females, thus explaining why they are so rarely met with in fÆces [but it is probable that they often escape notice from their small size.—J.W.W.S.].
Development.—The eggs, which often adhere together, contain a tadpole-like embryo, the thin tail of which is bent upwards ventrally; the embryo in a short time, given a sufficiently high temperature, passes into a second folded nematode-like embryonal stage, lying in the egg-shell, either in the fÆces, with which also numerous females pass out, or in the moisture of the groove between the buttocks, and they there await the opportunity of being reintroduced into man per os. It is
Fig. 347.—Oxyuris vermicularis: egg freshly deposited, with tadpole-like embryo. ×640.
Fig. 348.—Oxyuris vermicularis: egg twelve hours after deposition, with nematode-like embryo. ×640.
The opportunity for this is afforded every evening, as naturally the troublesome itching caused by the wandering of the worms is met by scratching and rubbing with the fingers. It is therefore possible that the eggs may even thus be introduced into the nose, where the young Oxyuris are perhaps hatched out, if they get high enough up on the moist pituitary mucous membrane. As a matter of fact, the larvÆ of Oxyuris have been found in the nose. Moreover, one can understand that the eggs of Oxyuris are transferred from person to person by the hand, directly or indirectly. This again explains the wholesale infections which occur in collective dwellings, after a person harbouring Oxyuris has been admitted into boarding-houses, etc. The primary infection may be also caused in other ways—by foods, fruits, vegetables and other articles that are eaten raw, and are polluted with the ova. Perhaps also flies or their excrement play a part in the distribution of the parasite, similar to that demonstrated by Grassi as taking place in the spread of the ova of Trichocephalus and TÆnia.
The assumption of a direct development without an intermediary host was first substantiated by Leuckart by experiments on himself and three of his students; about fourteen days after swallowing the eggs the Oxyuris has attained 6 to 7mm. in length; Grassi, and later on Calandruccio, infected themselves by swallowing adult female Oxyuris, with the same results. Heller found worms in the gut (appendix vermiformis) of a male child five weeks old.
Other species are: O. compar in the cat; O. curvula and O. mastigodes in horse, ass, mule; O. ambigua in the rabbit; O. poculum in the horse; O. tenuicauda in the horse. Many species occur in insects, especially in BlattidÆ and HydrophilidÆ (aquatic beetles).
Family. MermithidÆ.
Genus. Mermis, Dujardin, 1845.
With characters of the family.
Mermis hominis oris, Leidy, 1850.
Fourteen centimetres in length, 0·16mm. in breadth; mouth terminal; posterior extremity obtuse and provided with a recurved hook 50µ long.
The parasite was “obtained from the mouth of a child.” Stiles considers it to be probably a Mermis, possibly swallowed in an apple.
Agamomermis, Stiles, 1903.
Group name for immature MermithidÆ.
Agamomermis restiformis, Leidy, 1880.
This worm measures 65cm. in length, pointed anteriorly, the posterior extremity broadened and rounded off (1·5mm. in breadth); the mouth is terminal, without lips. Behind the mouth six papillÆ; the oesophagus measures 1·125mm. in length; the intestine appears to terminate blindly.
This parasite was obtained in West Virginia from the urethra of a young man, aged 20, who for a few days previous to expelling the worm passed turbid and bloody urine.
TECHNIQUE.
Preservation and Examination of Flukes.
Fixation.—(Method A.) (1) Place the flukes in a test tube or small bottle a quarter full of normal saline. Shake the contents as hard as possible (the object of this is to extend the flukes) for half a minute.
(2) Add immediately an equal bulk of saturated aqueous solution of corrosive sublimate and shake again as vigorously as possible for a few minutes.
(3) Transfer when convenient to 70 per cent. alcohol. (Before staining and mounting remove the sublimate with tincture of iodine.)
(Method B.) In case of large flukes, e.g., Fasciola hepatica, Fasciolopsis buski, compress the flukes between two glass slides with rubber bands or thread. Fix in sublimate or in absolute alcohol, or in 10 per cent. formalin.
(Method C.) Place the flukes in 10 per cent. formalin solution.
Staining is successfully effected by using quite dilute solutions of carmine or hÆmatein overnight. This is far preferable to using strong solutions, as it may be almost impossible to remove a too intense stain. Almost any dilute carmine solution suffices. One of the best is acetic-alum carmine (boil excess of carmine in a saturated aqueous solution of potash-alum for about fifteen minutes; add glacial acetic acid to the extent of 10 per cent.; let it stand for a week; filter). For use, dilute about thirty times with water. Place the flukes directly in the stain. Stain overnight or longer.
Differentiation.—In order to get the sharpest picture, it is best now to differentiate (but this may often be omitted) with acid alcohol (70 per cent. alcohol 100 parts, HCl 5 drops). Allow to act from one to twenty-four hours, according to the appearance of the flukes. Similarly, in staining with hÆmatoxylin solution, dilute twenty to thirty times so that the water is merely tinged with the stain. Differentiate as before. After staining, dehydrate, clear, and mount in balsam if required.
Clearing and Mounting.—(1) Carbolic acid (carbolic acid 94, water 6) is a very convenient clearing agent. It may be used for stained or unstained specimens. It will clear rapidly without previous dehydration. If it is required to mount a specimen permanently, transfer from carbolic to alcohol, then cedar-wood oil (or xylol, etc.), then balsam.
(2) Creasote.—Dehydrate the specimen, stained or unstained, transfer to creasote. If it is desired to mount permanently, transfer back to alcohol, then cedar-wood oil, then balsam.
(3) Cedar-wood Oil.—Preferable to xylol or oil of cloves. Dehydrate the specimen in alcohol. To mount permanently, transfer to balsam.
(4) Glycerine.—Vide under methods of preservation of ova; to mount permanently, transfer to glycerine jelly; subsequently to harden the jelly, expose to formalin vapour.
Of these media, carbolic acid has the greatest refractive index excepting that of balsam. The latter may, in some cases, render structures too transparent, and it may be advisable to use only glycerine or glycerine jelly.
Preservation of Ova in FÆces, Urine, Bile, etc.
Heat some 70 per cent. alcohol in a basin to about 60 to 70°C. (until bubbles begin to appear). Add the fÆces, etc., in the proportion of one part to about nine of fixative; keep stirring. Allow the sediment to settle. Transfer to a bottle with some fresh 70 per cent. alcohol.
Transference to Glycerine.—Prepare 5 per cent., 10 per cent., 20 per cent. solutions of glycerine in 70 per cent. alcohol. Pour off the alcohol in the bottle of fÆces, etc., and replace by 5 per cent. glycerine solution. Allow to stand an hour or so. Then in the same way replace the 5 per cent. by a 10 per cent. glycerine, and finally by a 20 per cent. glycerine solution. When in this latter expose freely to the air (protecting from dust), so as to allow the alcohol and water to evaporate. Add a few drops of glycerine from time to time till eventually the ova are in pure glycerine. (In a very moist climate it may be necessary to use lime or calcium chloride to dry the air.) To mount permanently transfer some of the sediment to glycerine jelly.
Preservation and Examination of Cestodes.
Fixation.—(1) Saturated aqueous corrosive sublimate.—Add to this glacial acetic acid to the extent of 1 per cent. (Note this fixative will dissolve the “calcareous corpuscles”; 10 grammes of sublimate to 160c.c. of water will give a saturated solution.) Warm the fixative to 70° to 80°C. (Avoid the use of needles.) Use plenty of fixative. Allow to act for a quarter of an hour or so. (a) Transfer to 70 per cent. alcohol. (It is advisable to remove the sublimate by the use of Lugol’s solution, or a solution containing tincture of iodine, adding this until the iodine colour is permanent.) Or (b) transfer for preservation to 10 per cent. formalin.
Or (2) 10 per cent. formalin.—In order to prevent contraction it is advisable to extend the tapeworm and keep it fixed by glass plates, or wind the worm around a wide glass tube or bottle, and then fix it.
Or (3) fix in hot alcohol.
Staining.—As under flukes. It is necessary to sacrifice portions of the tapeworm for this purpose, cutting out, e.g., mature segments, so as to study the topography of the genitalia.
Clearing.—As under flukes. To examine the hooks satisfactorily it is best to cut off the head with a sharp knife and mount. A certain amount of pressure is then advisable in order to view the hooks completely so as to measure them.
Preservation of Ova in FÆces, etc.
As under flukes.
Preservation and Examination of Nematodes.
Fixation.—(1) Thoroughly wash the worms to get rid of mucus, etc., by shaking up in warm saline (or water) till the washings are clean. Then transfer to 70 per cent. alcohol heated to about 70°C. It is absolutely necessary to use hot fixatives in order to extend the worms. If no alcohol or spirit is immediately available, drop the worms into hot water, or saline, and transfer later to 70 per cent. alcohol.
(2) Drop into hot 10 per cent. formalin.
Clearing.—(1) Carbolic acid, vide p.471.
(2) Creasote, vide p.471.
(3) Glycerine, vide p.472.
Staining.—In case of quite small Nematodes, e.g., AnguillulidÆ, carmine may be used, but as a rule staining is not advantageous.
Rolling.—In order to study the mouth parts, or bursa, etc., it is necessary to place the worm in any desired position. This is done as one would roll a penholder along the table by one’s finger placed on top of it. In the case of a worm, one edge of the cover-glass is placed over the worm, the other is supported by a strip of cardboard. By tapping the cover-glass the worm will now revolve as much as required provided it is round and straight. In certain cases it may be necessary for this purpose to cut off the head or tail. Roll these separately.
When a suitable position is got, the worm may be fixed in this position by pressure on the cover-glass, so as slightly to flatten it.
Mounting the Head.—If it is required to get an end view, it is necessary to cut off the head transversely as near the end as possible, and then mount.
Detection of Eggs (Bass and Hall).—Mix the fÆces thoroughly with ten times the volume of water. Filter through gauze. Centrifugalize the filtrate. Wash the sediment and centrifugalize. Repeat twice. To sediment add CaCl2 solution, sp. gr. 1250. The eggs float to surface. Pour off surface fluid. Dilute to sp. gr. 1050. Centrifugalize. Examine sediment, which contains practically all the eggs in the stool.
Detection of Small Nematodes.—Mix the fÆces thoroughly with water. Allow to settle for five minutes. Carefully decant off, or better, syphon off the fluid. Mix the sediment again with water. Allow to settle. Remove the fluid. Repeat several times. Examine the sediment in a Petri dish. As the fluid is poured off, the worms will be seen collected in the backwater. Remove them with a brush. Fix in hot 70 per cent. alcohol.
Cultivation of Larval Forms of Ancylostoma and Strongyloides.
A modification of the second method of Looss (p.455) is that of FÜlleborn. A glass filter funnel is lined with linen or with cotton wool dyed black with iron-tannin. On this is placed a layer of sterile sand, and on top of this the fÆces. The whole is moistened. The larvÆ hatch out and wander through the meshes of the wool, appearing on the edges of the same as white threads visible to the naked eye. With a platinum needle these can be easily removed. The glass filter can be placed on a glass cylinder, and this in another large stoppered cylinder containing caustic potash solution at the bottom, so that any larvÆ escaping from the funnel are killed.
D. ACANTHOCEPHALA, Rud.
Fig. 348a.—The male of Echinorhynchus augustatus. L., lemnisci; T., testicles; P., prostatic glands; P.r., sheath of proboscis, with ganglion; R.r., retractor of sheath of proboscis. 25/1.
Gutless, nematode-like worms that carry at their anterior end a retractile rostrum beset with hooks. In their adult condition they only live in vertebrate animals. During their larval stage they are often parasitic in invertebrate animals.
The Acanthocephala are elongated cylindrical worms, with a rounded posterior end. In some species an annulation is distinctly recognizable; they are, however, not segmented. The size varies according to the species, between about 5 to 10mm. and 40 to 50cm.; in general, however, there is a preponderance of the small species. The sexes are separate, and the males can easily be distinguished from the females without examination of the genitalia, as the females are both larger and thicker.
The body wall of Echinorhynchus is limited by a thin cuticle, which is attached inwardly to the hypodermis. In only exceptional cases a syncytium with large nuclei, even in the adult condition, is represented by the hypodermis; and in it fibre systems, the elements of which run in layers in various directions, appear, and it is only towards the interior from these strata of fibres that the nuclei of the hypodermis are found. As a rule, these fibres, at all events the radiary fibres, are regarded as muscles. Hamann describes them as elastic fibres, which lie in a viscid gelatinous connective substance (transformed protoplasm?); a lacune system filled with a granular fluid, the central part of which are two longitudinal lacunes lying at the sides, also belongs to the cutaneous strata, as do the so-called lemnisci, two short, flat organs suspended in the body cavity, and the pedicles of which are attached anteriorly at the border between the rostrum and body; their structure as well as their origin permit them to be traced to the skin (fig.348A).
Finally, inwardly below the skin there follows a layer of annular, and after these a layer of longitudinal muscles, the structure cells of which remain present in the residues, carrying nuclei. The motor apparatus of the rostrum, the sheath of the rostrum, and the lemnisci also belong to the muscular system. The rostrum represents a finger-shaped hollow process of the cutaneous layer; but, according to Hamann, it originates from the entoderm and passes through the skin secondarily. It is covered by a thin cuticle, and as a rule contains a large number of regularly placed chitinous hooks that adjoin a granular formation tissue. From the base of the rostrum springs a tubular hollow muscle extending into the body cavity; this is the RECEPTACULUM PROBOSCIDIS, from the base of which again bundles of longitudinal muscles originate, which pass along its axis and that of the rostrum itself, and are inserted at the inner surface of its anterior end (RETRACTOR PROBOSCIDIS). These muscles when they contract invaginate the proboscis and draw it into the receptaculum; when reversed they act again as PROTRUSOR PROBOSCIDIS. The whole of the anterior body, however, can be invaginated, and for this purpose there is a muscle that originates from the body wall at a variable distance back, and which is joined to the receptaculum (RETRACTOR RECEPTACULI); there is also a bell-shaped muscle which springs from the body wall behind the lemnisci in rings, and passes forward to the spot of attachment of the lemnisci.
The nervous system consists of a cluster of ganglia situated at the base of the rostrum, from which three nerves pass towards the front and two towards the back. No sensory organs are known.
The excretory organs, according to Kaiser, lie at the upper border of the ductus ejaculatorius in the male and at the so-called bell in the female. Here they
Sexual Organs.
(a) Male Organs.—The greatest part of the male genital apparatus is contained in a muscular sheath—the ligament—which originates at the posterior end of the receptaculum proboscidis, passes along longitudinally through the body cavity, and is inserted at the posterior end of the worm. The two oval testicles usually lie one behind the other; their vasa efferentia unite sooner or later into a vas deferens which passes backwards, and finally terminates in the penis; the terminal portion of the conducting apparatus is surrounded by six large glandular cells (prostatic glands) the excretory ducts of which open into the vas deferens. The penis itself is placed at the base of a bell-shaped invagination of the posterior end, the bursa, which is everted during copulation.
Fig. 348b.—Anterior portion of the female apparatus of Echinorhynchus acus. On the left seen from behind, on the right seen from the front. F, inferior orifice of the bell; B, bell; Lig, ligament; M, mouth of bell; Ut, uterus. Magnified. (After Wagener.)
(b) Female Organs.—There are only two ovaries present in the ligament during the larval stage. During the course of growth they divide into accumulations of cells (placentulÆ, loose or floating ovaries), which finally cause the ligament to burst
The eggs are already fertilized in the body cavity, and in this position go through their development to the formation of the embryo. Completely developed eggs are surrounded by three shells, and are generally fusiform. The eggs agglomerate in masses in the uterus until they are finally deposited through the vagina and vulva. For the further development, the transmission of the eggs into an intermediary host—usually a crustacean or an insect—is necessary; the metamorphosis is very complicated; but this transmission may be very easily effected artificially by feeding suitable crustaceans (Asellus, Gammarus, etc.) with the eggs of Acanthocephala; this being the only method of inducing the larva to hatch out so that its structure may be studied. The larva appears in the form of an elongated, somewhat bent body, at the stumpy anterior end of which there is a crown of hooks or spines, whereas the posterior end is pointed. Especial retractors draw in the hook-beset anterior surface, and an elastic cushion beneath them jerks them forward again when required. In the middle of the body a roundish heap of small cells is seen, from which the entire body of the Echinorhynchus originates, even to the cutaneous layer; the latter is also the larval skin in which the small Echinorhynchus gradually grows. The development of all the organs takes place within the intermediary host, and the parasite only needs to be imported into the terminal host to attain the adult stage after a certain growth. In some cases, however, a second intermediary host is utilized.
Species of Acanthocephala only occur exceptionally in human beings.
Echinorhynchus gigas, Goeze, 1782.
Syn.: TÆnia hirudinacea, Pallas, 1781.
Fig. 348c.—Egg of Echinorhynchus gigas. 300/1. (After Leuckart.)
The body is elongated, gradually decreasing in thickness towards the back. The rostrum is almost spherical, and is beset with five or six rows of recurved hooks. The males measure 10 to 15cm. in length, the females 30 to 50cm.; the eggs are provided with three shells, of which the middle one is the thickest. The eggs measure 0·08 to 0.1mm. in length. The giant Echinorhynchus occurs especially in the intestinal canal of the domestic pig; it is less common in other mammals. It bores deep into the mucous membrane with its rostrum, and causes an annular proliferation around the perforated spot; occasionally also it causes perforation of the intestine.
It is doubtful whether the giant Echinorhynchus occurs in man. Leuckart admitted that there were a few positive cases. According to Lindemann, Ech. gigas occurs in human beings in South Russia, and its presence is not rare. This statement, however, has not been confirmed. Its presence in man is by no means impossible, as its intermediary host, the cankerworm, or cock-chafer (Melolontha), is, according to Schneider, occasionally eaten raw by human
Echinorhynchus hominis, Lambl, 1859.
This term is applied to an Echinorhynchus found by Lambl in the intestine of a boy who had died of leucÆmia; the worm was 5·6mm. in length, and the almost spherical head was beset with twelve transverse rows of hooks.
Echinorhynchus moniliformis, Bremser, 1819.
The male is 4cm. in length, the female 8cm. long. This species lives in the intestine of field-mice, rats, marmots and Myoxus quercinius. A beetle (Blaps mucronata) is the intermediary host.
This species has also once been artificially cultivated in man (Grassi and Calandruccio).
E. GORDIIDAE.
Very long thin worms similar to FilariÆ, which, in their adult condition, live free in brooks, pools and springs; the mouth and the commencement of the intestine are obliterated; there are no lateral ridges, and the muscular system presents a structure different to that of the Nematoda. The posterior end of the male is split, and spicules are lacking; there are two testicles. In both sexes the genitalia discharge through the terminal gut.
The larvÆ, which carry a rostrum beset with hooks, force themselves into the larvÆ of water-insects; more rarely they invade molluscs, and they then become encysted within the body of the host. According to Villot, at least a part of them attain the intestine of fishes, where they again become encysted, and after a period of rest they travel into the tissues of their hosts, and finally again reach the exterior by way of the intestine, where they then become adult. In most cases, however, the gordius larvÆ are taken up by predacious water insects; they live for a while in the body cavity of these insects, undergo a metamorphosis, and finally wander into the water.
A few species invade man accidentally with water, in which case they are usually vomited up:—
Gordius aquaticus, Dujardin, 30 to 90cm. in length (Aldrovandi, Degland, Siebold, Patruban).
Gordius tolosanus, Duj., 11 to 13cm. in length (Fiori).
Gordius varius, Leidy, 10 to 16cm., female, up to 30cm. in length (Diesing).
Gordius chilensis, Blanch. (Guy). Gordius villoti, Rosa (Bercutti, Camerano); Gordius tricuspidatus, L. Def. (R. Blanchard), Gordius violaceus, Baird (Topsent), and Gordius pustulosus, Baird (Parona).
F. HIRUDINEA s. DISCOPHORA (Leech).
Fig. 348d.—The internal organs of the leech. The creature has been opened from the dorsal surface, and part of the intestine has been removed. The testicles, with vas deferens, may be seen between the blind ducts of the intestine; beyond these on either side the segmental organs. The female genital organs are in front of the most anterior pair of testicles. (After Kennel.)
The Hirudinea, which have been appropriately included amongst the Annelida, differ in many respects from the typical members of the group; their body is long and flat, it lacks the parapodia that are characteristic to all forms of Annelida; but, on the other hand, possesses a terminal posterior sucker, and in many species there is also an anterior sucker. The mouth is terminal at the anterior end, the anus lies dorsally above the posterior sucker (fig.348D). The body is segmented, but this is less manifest in the body covering than it is in the arrangement of the internal organs; the segmentation, nevertheless, is also indicated exteriorly by the appearance of the cutaneous sensory organs which correspond to the segments. This shows what the condition of the ganglia in the abdominal ganglion chain has taught us, that the anterior and the most posterior segments are considerably abbreviated—a part of the latter taking part in the formation of the suctorial organs. In a great many species the skin is distinctly annulated, four or five of such rings, at least in the central region of the body, appearing on one segment of the body. The condition of their body cavity is another peculiarity of the Hirudinea; it is narrowed by the powerful development of the connective tissue and the muscular system into four tubular sinuses, which have the appearance of blood-vessels. There are usually one dorsal and one ventral median trunks, as well as two lateral trunks; in addition, a particular blood-vessel system exists.
The skin consists of a very thin cuticle that is cast off from time to time; it is secreted by the underlying cylindrical epithelium, which contains numerous goblet cells. The muscular system is strongly developed; it consists of long tubular fibres, which run circularly, longitudinally and in the dorso-ventral direction; the muscular system is subject to a particular expansion in the clinging organs and at the commencement of the intestine. On the whole, the alimentary canal represents a tube running straight from the mouth to the anus, which possesses a number of blind sac-like protuberances at the sides varying according to the species. The most anterior section, the pharynx, in the leeches with maxillÆ carries three chitinous, semicircular plates furnished with teeth—the jaws—which serve to tear up the epidermis in order to open the blood-vessels; in the leeches with rostra a long protractile proboscis rises from the base of the elongated pharynx. Numerous salivary glands, the secretion from which possesses toxic properties, discharge into the pharynx. The oesophagus, which follows the pharynx, and to the exterior of which numerous radiary muscles are fixed, is a suctorial organ in its entire structure. The nutriment in the larger species consists of the blood of vertebrate animals, in smaller species and in the young stages the food consists of small invertebrate animals.
The NERVOUS SYSTEM exhibits the typical structure of other segmented worms; the sensory organs consist of the previously mentioned goblet-shaped cutaneous sensory organs, of the organs of taste, and of eyes, the latter frequently being present in large numbers.
The EXCRETORY or segmental organs exhibit many peculiarities, which cannot, however, be detailed here. They commence with funnels in the lacunes of the body cavity, and usually discharge on the ventral surface.
Almost all the Hirudinea are hermaphrodite and copulate reciprocally. The two ovaries are very small, and the oviducts that proceed from them soon unite into a common duct, which then passes into the uterus and discharges through the short vagina in the median line of the ventral surface behind the male organs into the so-called clitellar region. The male sexual apparatus consists of symmetrically arranged testicles, varying in number according to the species, the short vasa efferentia of which, one by one, run into the vas deferens, passing towards the front on each side. In front, at about the level, or a little in front, of the female genitalia, the two vessels pass into a convoluted mass of tubes to the so-called epididymis, and then discharge into the single protractile penis (fig.348D).
All leeches deposit so-called COCOONS. These are small barrel-shaped or pouch-like bodies, which are surrounded by a thicker shell and contain a number of eggs in a large mass of albumen; the albumen originates from glands of the generative organs, the shell substance from cutaneous glands of the clitellar region.
Family. GnathobdellidÆ (Leeches with Jaws).
These are distinguished by the possession of usually three jaws in the pharynx; the body consists of twenty-six segments. The posterior sucker is large and flat; the anterior sucker is smaller. The Hirudinea have five pairs of eyes, the NephelinÆ have four pairs.
Genus. Hirudo, L., 1758.
The entire body consists of 102 annulations, five appearing on one segment in the central region of the body. The pharynx has three semicircular jaws, the arched border of which is beset with numerous teeth (50 to 100). The male sexual orifice lies between the thirtieth and thirty-first rings, the female orifice between the thirty-fifth and thirty-sixth. There are numerous species, some of which are utilized for medicinal purposes.
Fig. 348e.—Hirudo medicinalis. a, anterior end, with open buccal cavity, with the jaws, J, at the; b, one jaw isolated. (After Claus.)
Hirudo medicinalis, L., 1758.
It occurs in numerous colour varieties, one of which has been designated Hirudo officinalis, Moq.-Tandon. Usually the dorsal surface is greyish-green and is marked with six rusty-red longitudinal stripes. The ventral surface is olive-green, more or less spotted with black, and marked at the sides with a black longitudinal line. The length averages 8 to 12 to 20cm. This leech lives in swamps, ponds and brooks, overgrown with plants and having a muddy bed. The cocoons are deposited in the soil at the sides. Europe, as well as North Africa, is its home. At the present day it has been exterminated from most parts of Central Europe, but it is still very common in Hungary. Its use for medicinal purposes is well known. A large leech can suck about 15grs. of blood, and about the same amount is lost through secondary hÆmorrhage.
Hirudo troctina, Johnston, 1816.
Syn.: Hirudo interrupta, Moq.-Tandon, 1826.
This species measures 8 to 10cm. in length. The back is greenish, with six rows of black spots surrounded by red; the lateral borders are orange-coloured; the abdomen spotted or unspotted. Its habitat is in North Africa and Sardinia. It is applied medicinally in England, Spain, France, Algeria, etc.
Genus. Limnatis, Moq.-Tandon, 1826.
Nearly related to Hirudo, but is differentiated by a longitudinal groove on the inner surface of the upper lip of the anterior sucker. The jaws are furnished with over 100 very sharp toothlets.
Limnatis nilotica, Savigny, 1820.
Syn.: Bdella nilotica, Sav.; L. nilotica, Moq.-Tandon; HÆmopis (vorax), Moq.-Tandon, 1826, p. p.; HÆmopis sanguisuga, Moq.-Tandon, 1846 (nec Hir. sanguis, Bergm., 1757).
This species measures 8 to 10cm. in length, and becomes gradually more pointed towards the front; the body is always soft. The back is brown or greenish, and has usually six longitudinal rows (rarely only two or four) of black dots. The abdomen is dark; but numerous colour variations occur.
The native place is North Africa, especially the coastal regions; it is also found in the Canaries, the Azores, Syria, Armenia, Turkestan, perhaps also Southern Europe. It is taken into the mouth with drinking water, and may settle in the pharynx, larynx, oesophagus, and nasal cavities of human beings. This species has also been observed in the vagina and on the conjunctiva. It is equally fond of attacking domestic animals.
Hirudo mysomelas (Senegambia) and Hirudo granulosa (India) are placed with this genus, and, like our leech, are also used for medicinal purposes.
Genus. HÆmadipsa, Tennent, 1861.
These leeches live on land, and measure 2 to 3cm. in length. About a dozen species are known. They are a veritable scourge to persons in the tropics (Asia, South America), as they attack them to suck their blood. They are able to force their way even under close-fitting garments, so that it is difficult to protect oneself from their assaults (HÆmadipsa ceylonica, Bl., and other species).
Family. RhynchobdellidÆ (Leeches with Rostrum).
These are furnished with a proboscis in lieu of the jaws; the segment consists of three annulations.
Genus. HÆmentaria, de Filippi, 1849.
HÆmentaria officinalis, de Fil.
Inhabit Mexico, where they are used for medicinal purposes.
Genus. Placobdella, R. Blanch.
Placobdella catenigera, Moq.-Tandon.
Indigenous to South Russia, Hungary, Italy and South France. It is a parasite of the swamp turtle, but frequently attacks human beings.
G. ARTHROPODA (Jointed-limbed Animals).
BY
FRED. V. THEOBALD, M.A.
Bilaterally symmetrical segmented animals which are covered with a thick cuticle that is frequently calcareous (Crustacea), but always thinner between the segments; they carry (primitively) a pair of jointed appendages on every segment.321 The segments of the body are uniform in certain regions, but differ from those of contiguous regions, so that it is easy to distinguish three parts (head, thorax and abdomen), each composed of segments. The cephalic segments are always formed into a uniform head, the segmentation being scarcely recognizable at either end; the thoracic segments may also fuse, or part or all of them may coalesce with the head; the abdomen, as a rule, retains its segmentation, but this may possibly also be lost, in which case it is [sometimes] united to the cephalothorax. The structure of the three regions depends mostly on the varying form and function of the appendages: those on the head are primitively locomotive organs (and frequently are still so in the early stages), but they become transformed into feelers and mouth-parts (mandibles, maxillÆ); the limbs of the thorax, however, usually retain their ambulatory functions, as frequently do those of the abdomen; sometimes, however, the abdominal limbs disappear, entirely or partly; in the latter case they are then utilized for other purposes.
In their organization the Arthropoda approach the segmented worms.
The Arthropoda are generally divided into five groups (Crustacea,322 Protracheata, Arachnoidea, Myriapoda,323 and Insecta or Hexapoda), of which only the Arachnoidea and the Hexapoda interest us here.
A. ARACHNOIDEA (Spiders, Mites, etc.).
The head and thorax are always united together; the abdomen is either segmented or without exterior segmentation, in which case it is united with the cephalothorax.324 The number of pairs of appendages
There are eight or ten orders of Arachnoids,326 of which, however, only two, the Acarina and the Linguatulida, have to be considered here.327
Order. Acarina (Mites).
Small Arachnoids, the three parts of the body of which are, as a rule, coalesced; it is only rarely that a faint line indicates the division between a cephalothorax and abdomen. The two appendages on the head are designed for biting or puncturing and sucking, and vary according to their use. The chelicerÆ328 are fang-like jaws or puncturing bristles forming a kind of rostrum, the pedipalpi are claw-like or shear-shaped, or form a suctorial proboscis.329 The four pairs of legs are usually well developed, more rarely they are rudimentary or have partly vanished; many parasitic forms are provided with pedunculated suckers [ambulacra—F.V.T.]. Respiratory organs (tracheal tufts) may be present or absent. The nervous system is reduced to a minimum, eyes are usually lacking. The intestine, situated in the central part, generally has three blind appendages; the anus is situated on the venter above the posterior end. Sexes separated; nearly all the species deposit eggs, from which six-legged larvÆ hatch. The Acarina live either free in the water or in moist soil, or they are parasitic on plants and animals.330
Family. TrombidiidÆ (Running Mites).
Soft-skinned Acarina with tracheÆ and with two eyes, usually pedunculated; they are often brightly coloured; chelicerÆ lancet- or claw-shaped; pedipalpi claw-like; legs composed of six segments, with suctorial discs between the terminal ungues.331 LarvÆ six-legged. To the latter belong the larvÆ of several species of Trombidium such as:—
Genus. Trombidium, Latreille (and Leptus).
Leptus autumnalis, Shaw, 1790.
Fig. 349.—Leptus autumnalis, with so-called sucking proboscis. Enlarged. (After Gudden.)
Leptus occur as parasites in the human skin and cause a cutaneous disease known as autumn erythema, and produce a very unpleasant sensation on account of the troublesome itching; in children it is very often accompanied by fever.332
Formerly these mites were considered adult forms, but when they were recognized as mite larvÆ they were taken for those of the spider-mite (Tetranychus telarius); the investigations of Hanstein, however, showed this to be a mistake. When Henking first investigated the development of Trombidium fuliginosum, parasitic in the larval stage on vine-fretters, he demonstrated the occurrence of a form very similar to Leptus autumnalis, and the “autumn, grass, or gooseberry” louse was commonly designated the Trombidium larva. Even before Henking’s work it had been described by MÉgnin as the larva of Trombidium holosericeum, a red-coloured species, frequently occurring in spring and summer on the ground, trees, etc. This assumption, however, as Moniez was the first to explain, is not correct;
Fig. 350.—Leptus autumnalis: the so-called proboscis is formed around the hypopharynx sunk into the skin. 100/1. (After Trouessart.)
The above-mentioned forms invade the skin of man by means of their oral apparatus, by preference invading the orifices of the sebaceous glands so as to suck the blood; around the point attacked there arises a wheal about the size of a lentil, and around the inserted hypopharynx a fibrinous secretion, the “proboscis,” which, however, is a product of the host, just as chitinous secretions are provoked by Trombidia parasitic on Arthropods.
Further species, analogous in habit to Leptus autumnalis, are described by Riley from Central and South America as L. americanus and L. irritans.
[L. autumnalis attacks small mammals by preference, such as moles and hares, which are often literally covered with them. Dogs are also subject to their attack, and cats suffer similarly. This mite also frequently appears in colonies on cows; cavalry horses after autumn manoeuvres often suffer from an erythematous affection about the hocks and knees due to this pest.
[A number of Leptus, so far undescribed, occur abroad which attack man in the same way as L. autumnalis in Europe. Dr. Durham has brought me specimens from British Guiana called bÊte rouge; this species works under the skin much as does our European species, but it is very distinct, being considerably larger.—F.V.T.]
Trombidium tlalsahuate, Lemaire, 1867.
T. tlalsahuate occurs in Mexico under conditions similar to those of Leptus here. It also frequently attacks men, and especially fastens itself on to the eyelids, in the axillae, navel, or on the prepuce; it induces itching and swelling of the parts affected, and sometimes even causes suppuration; the symptoms, however, generally disappear after a week and remain localized.333
Other species of mites which attack man are reported, mostly by travellers, from various other places; zoologically, however, there is little known about them. The pou d’agouti in Guiana, niaibi in New Granada, colorada in Cuba, mouqui in Para, and the buschmucker in New Guinea represent a few of these.
Akamushi or Kedani.
In a few districts of Japan there occurs a serious illness, with a mortality of 40 to 70 per cent. It is called river or flood fever, and the Japanese doctors have connected it with a small mite (akamushi, kedani). Baelz has opposed this opinion on the grounds that he has repeatedly observed the same species of mite in his dwelling without any subsequent illness occurring. According to KeÏsuke Tanaka, however, a connection certainly does exist, inasmuch as the akamushi, like Leptus, attacks persons to suck blood. If the mite is not removed, or if the spot attacked is injured by scratching, etc., a papule surrounded by a red area forms, and a pustule ensues; and finally a black scab covers the seat of injury. The lesion becomes the point of entrance of bacteria, especially a species of proteus which produces river fever. If the mites are carefully removed no general illness takes place.
Fig. 351.—The kedani mite. Enlarged. (After Tanaka.)
The orange-red mites, which we only know in their larval condition, measure 0·16 to 0·38mm. in length by 0·10 to 0·24mm. in breadth. They have leg-like palpi with three joints, hirsute bodies, and very hairy legs composed of five segments, terminating with three ungues.
Family. TetranychidÆ (Spinning Mites).
These have tracheÆ and eyes; the palpi are composed of four segments, of which the last but one has a powerful claw. The legs have six segments with sucker discs between the claws.
[The red spiders or spinning mites (Tetranychi) are usually placed in the family TrombidiidÆ.—F.V.T.]
Genus. Tetranychus, Dufour.
Tetranychus molestissimus, Weyenbergh, 1886.334
Found in Argentine and Uruguay on the under surface of the leaves of Xanthium macrocarpum; it attacks mammals and men, producing severe itching, accompanied by fever in the latter.
It has been asserted by Haller that the Cape ailment (Port Natal sickness) is caused by mites, but this statement has been contested.
Tetranychus telarius, L., 1758,335 var. russeolus, Koch.
Fig. 352.—Tetranychus telarius var. russeolus, Koch. Enlarged. (After Artault.)
This common spinning mite likewise attacks human beings, but the papules produced by it very soon disappear.
Family. TarsonemidÆ.
A family distinguished by complete sexual dimorphism, the species of which are provided with tracheÆ; the legs have five segments; the terminal segments of the front pair of legs of both sexes possess a claw; the terminal segment of the posterior pair of legs of the male likewise has a claw. In the female this pair of legs, like the second and third pairs of both sexes, is provided with two hooklets and a sucking disc. The cuticle of the body on the back is “annulated.”
[This family of small transparent mites live normally as plant parasites. The last two pairs of legs are widely separated from the two front pairs.—F.V.T.]
Genus. Pediculoides.
Pediculoides ventricosus, Newport, 1850.
Syn.: Heteropus ventricosus, Newport, 1850; Acarus tritici, LagrÈze-Fossot, 1851; Physogaster larvarum, Lichtenstein, 1868; SphÆrogyna ventricosa, LaboulbÈne and MÉgnin, 1885.
Males are oval in shape, 0·12mm. in length and 0·08mm. in breadth, flattened. There are six pairs of chitinous hairs on the dorsal surface and a lyre-shaped lamella on the posterior part. The female in the non-gravid state is cylindrical in form, 0·2mm. in length and 0·07mm. in breadth; when gravid the posterior part of the body becomes enlarged into a ball, which may attain 1·5mm. in size, as in the case of Pulex penetrans and of the female Termites. On emerging the young are already provided with four pairs of legs and copulate soon after birth.
Fig. 353.—Pediculoides ventricosus. a, male; b, young female; c, gravid female. Enlarged. (After LaboulbÈne and MÉgnin.)
These animals live on the stalks of cereals, and feed on vegetable and animal juices; they are also found on corn-infesting insects. They invade the barns and seek out the insects living in the dry grains of corn, or wait for an opportunity of obtaining food. They have been repeatedly observed on human beings, particularly labourers occupied in handling grain; their bite causes severe irritation, local elevation and reddening of the epidermis, as well as fever. It cannot be positively asserted that all cases of the occurrence of cereal mites on man relate to P. ventricosus, as the descriptions are often insufficient. Geber states that one form is Chrithoptes monunguiculosus, or Acarus hordei; Flemming mentions Tarsonemus uncinatus; Koller Oribates sp.; and Karpelles Tarsonemus intectus.
[The pregnant female Pediculoides has a large round inflated abdomen, in which the ova hatch and the young mature. Later they escape from the parent as adults.—F.V.T.]
Genus. Nephrophages.
Nephrophages sanguinarius, Miyake and Scriba, 1893.
Fig. 354.—Nephrophages sanguinarius: male, ventral surface. Enlarged. (After Miyake and Scriba.)
Males measure 0·117mm. in length and 0·079mm. in breadth; females up to 0·360mm. in length by 0·120mm. in breadth. The head is provided with two very large scissors-like jaws and two large round eyes. The legs are composed of five segments and are all of equal length; the three anterior pairs of legs have pedunculated ambulacra, the posterior ones terminate in a claw. The cuticle on the back is thickened in three places, shield-like; the abdominal surface without scutellum is longitudinally striped and is beset with chitinous hairs. Colour greenish to brownish-yellow. Eggs 0·046 to 0·040mm.
Fig. 355.—Nephrophages sanguinarius: female, dorsal aspect. Enlarged. (After Miyake and Scriba.)
The authors discovered these mites, but always dead, in the urine of a Japanese suffering from fibrinuria complicated with chyluria and hÆmaturia. They surmised that they were endoparasites, probably situated in the kidney; but this view is not convincing, though they also report that for a week, day after day, the mites were found in the patient’s urine, as well as in urine drawn off by means of a catheter, and in the water used to wash out the bladder (one or two specimens and an egg). The statement that these mites have large eyes makes the discovery suspicious, to say the least. The significance of the discovery is not supported by the further statement that Disse is supposed to have found an encapsuled mite closely related to the Tyroglyphides on the wall of the vena cava.
In the case of Marpmann, who found a dead Acarid in the urine of a man suffering from chronic nephritis, and in whom later examinations proved negative,
We are certainly acquainted with mites living endoparasitically, namely, the CysticolÆ, AnalgesinÆ, of which Laminosioptes gallinarum live in the intramuscular and subcutaneous connective tissue of fowls, and Cytoleichus sarcoptoÏdes in their air sacs. Another kind of mite (Halarachne halichoeri) is occasionally found in the nasal mucous membrane of the seal (Halichoerus grypus), and, quite recently, Pneumonyssus simicola, which is more nearly related to Halarachne, has been found in the lung of Cynocephalus sp. It is therefore not improbable that endoparasitic mites are found in man; but no definite discovery has yet been made.
Family. EupodidÆ.
Small tracheate mites, with moderately long or short pedipalpi, composed of four segments, of which the last segments bend; chelicerÆ forceps-shaped, with serrated edges; legs with two claws, more rarely with one, and terminating in a tuft ornamented with fine hairs; genital orifices on the abdomen, surrounded by a circle of little hairs. Most species live free—one lives parasitically on the bodies of slugs.
Genus. Tydeus, Koch.
Tydeus molestus, Moniez, 1889.
Fig. 356.—Tydeus molestus: seen in profile. Enlarged. (After Moniez.)
Male, 0·2mm. in length, 0·125mm. in breadth. Females, 0·225mm. in length, 0·135mm. in breadth; gravid female 0·315 to 0·360mm. in length and 0·180mm. in breadth. They were observed by Moniez on an estate in Belgium, whither the creature had apparently been imported twenty-five years previously with Peruvian guano; they appeared regularly in the summer and remained until the first frost set in; they were found on grass-plots, on trees and bushes in masses; they regularly attacked human beings, mammals and birds, tormenting their hosts in a terrible manner.
Family. GamasidÆ (Coleopterous or Insect Mites).
ChelicerÆ chelate or styliform; pedipalpi filiform; the legs are composed of six segments with two terminal ungues and a bladder-like sucking disc [caruncle—F.V.T.]. Stigmata situated between the third and fourth pairs of legs; the cuticle thickened, leather-like; no eyes; the larvÆ have six legs.
The GamasidÆ are predaceous on small insects and other mites; some are parasitic on insects, and one is noticeable as a pest on birds, etc.
Genus. Dermanyssus, DugÉs.
Dermanyssus gallinÆ, de Geer, 1778.
Syn.: Pulex gallinÆ, Redi, 1674; Atarus gallinÆ, de Geer, 1778; Dermanyssus avium, DugÉs, 1834.
The male measures 0·6mm. in length by 0·32mm. in breadth; the female 0·7 to 0·75mm. in length by 0·4mm. in breadth. The body is somewhat pear-shaped; the colour whitish, reddish, or reddish-black, according to the contents of the intestine. The legs are fairly short and strong. During the day they live concealed in the nests, cracks, etc., of the hen-house, and at night attack the inmates in order to suck their blood; they rarely remain long on the birds. They have been repeatedly found on persons, on whose skin they produce an itching eruption.
Fig. 357.—Dermanyssus gallinÆ. Enlarged. (After Berlese.)
Fig. 358.—Dermanyssus hirundinis. 40/1. (After Delafond.)
Dermanyssus hirundinis, Hermann, 1804.
Syn.: Acarus hirundinis, Herm., 1804.
Of a brownish colour, 1·2 or 1·4mm. in length; lives in the nests of swallows and is occasionally found on man.
[The red hen mite (Dermanyssus gallinÆ) not only attacks poultry and man, as stated above, but is found on all birds and many mammals. The D. gallinÆ is the same as D. avium. The species found in swallows’ nests is also said to be the same. This mite can remain for weeks without any food from its normal host. They only attack man when entering or cleaning dirty and neglected fowl-houses; they do not produce a true dermatosis. They chiefly attack the backs of the hands and forearms of those who constantly attend poultry and give rise to symptoms similar to the papular eczema of scabies. That they may remain some time upon
Genus. Holothyrus.
Holothyrus coccinella, Gervais, 1842.
Measures 5mm. in size; lives on birds in the Island of Mauritius; ducks and geese frequently fall victims to its bite; it also attacks human beings, on whose skin it causes severe burning and swelling, but no reddening; it may be dangerous to children, especially by settling in the oral cavity.
Other Gamasides occasionally occur in man, for instance, according to Moniez, Leignathus sylviarum, Canestr. et Fanzago; according to Neumann LÆlaps stabularis. The former live normally in the nests of various species of Sylvia, LÆlaps on dried vegetable substances, also in houses.
[Marchoux and Conoy (Bull. Soc. Path. exot., 1912, v, No. 10, pp. 796–798) found Leishman granules in LÆlaps echidninus. It is assumed that Leishman granules may be found in most Arachnoids, and have no connection with SpirochÆta.—F.V.T.]
Family. IxodidÆ (Ticks).
Comparatively large Acarines with a leathery skin; they are flattened in form, but after sucking blood the abdomen becomes spherical; the chelicerÆ are rod-like and possess a serrated terminal joint, bent hook-like; the median parts of the pedipalpi (maxillÆ) form a rostrum furnished with barbed hooks (fig.359); the maxillary palpi themselves are club-like or rounded; the legs are composed of six segments with two terminal ungues, often also with “sucking discs”; the stigmata are at the sides of the body, posterior to the fourth or third pair of legs. The larvÆ are six-legged.
[The true ticks (IxodidÆ) are all blood-suckers, and as far as is known they do not take vegetable food at all. Not only are the IxodidÆ important as actual parasites, but they are most so on account of the fact that they are the active agents in carrying various diseases in animals and apparently in man. It has been conclusively proved that the bont tick (Amblyomma hebrÆum) is the carrier of the fatal “heart-water fever” so rife amongst sheep in South Africa, that the dog tick (HÆmaphysalis leachi) is the agent by which the protozoa that cause malignant jaundice in dogs are distributed, that
[The egg gives rise to the larval form, the so-called “seed-tick” stage. At first these minute specks are pallid and soft, but they soon harden and darken in colour. These larvÆ are six-legged and crawl up grasses and various plants, and there await a passing host, waving their two front legs in the air and becoming attached by this means. The larval ticks feed upon the blood of the host, and when replete fall to the ground, the body becoming inflated in the meanwhile. These larvÆ may remain on the host only two days, or they may remain much longer. Eventually they moult on the ground and change to the nymph or pupal stage, which has four pairs of legs. This pupa acts just as the larva, crawls up plants and waits to regain the host. After a time the nymphs, having gorged themselves with blood, fall off and remain on the ground for nearly three months; they then moult and become adult males and females. In about ten days they assume their normal colour and regain the host afresh; the female gradually swells until she attains that large inflated form so characteristic of ticks. The male does not swell, but nevertheless feeds upon the host and fertilizes the female.
[The act of coitus is strange: the male tick inserts its rostrum and other mouth organs into the sexual orifice of the female, between the base of the posterior pair of legs. The males then die and the females fall to the ground and deposit the ova. There are variations in the different species, of course, from those given above, which apply solely to Ixodes reduvius. The larvÆ and nymphs seem to attack most animals, but the adults mainly keep to the same host. The periods in the life-cycle of ticks not only vary in the different species, but in each species according to climatic conditions; for instance, in the bont tick (Amblyomma hebrÆum, Koch), Lounsbury has shown that the development is rapid in summer, slow in winter. The period from the time that the female drops to the time she commences to lay eggs varied in specimens observed by him from twelve days in summer to twelve weeks in winter, and the complete period from the dropping of the female to the hatching of the eggs, from eleven weeks in summer to thirty-six weeks through the winter. Other stages vary in a similar manner.
[Ticks may live a long time away from the host provided they are supplied with a certain amount of moisture. Mr. Wheler kept dog ticks (Ixodes plumbeus) in the larval stage for ten months; the pupÆ, male and female, of I. reduvius for six months.
[I have kept Ornithodorus moubata alive for eighteen months without food.
[In many species moulting takes place off the host, but in I. bovis,
[Two species are of special importance, namely Ornithodorus moubata, Murray, which may infect human beings with the spirillum of African tick fever, and Dermatocentor reticulatus var. occidentalis, which is said to be the carrier of Rocky Mountain spotted fever.
Classification of IxodidÆ.
[The ticks, or IxodidÆ, are divided into two groups, known as (1) ArgantinÆ, (2) IxodinÆ. The ArgantinÆ are told from the IxodinÆ by the absence of dorsal or ventral shields in both sexes, and also by the rostrum being placed beneath the cephalothorax, which covers it over: except in the larval stage, in which it is subterminal, and in the pupal, when it partly projects. Legs nearly equal in length. The sexual orifice is situated between the two first pairs of legs. The males usually smaller than the females.
[The IxodinÆ have the legs unequal, of six segments with two false segments, making them look as if composed of eight segments. The rostrum is terminal and never hidden beneath the body. The sexual orifice is situated between the bases of the first three pairs of legs. In the males the orifice is obsolete or very rudimentary, sexual intercourse being effected by the rostrum. The males are smaller than the females. The shield in the females never covers so much as one-half of the body even when fasting, also in the larvÆ and nymphs; but in the males, which do not distend, the shield covers the body entirely, or all but a narrow margin. The IxodinÆ are divided into two groups: (i) the IxodÆ, and (ii) the RhipicephalÆ. The former have a long proboscis reaching nearly to the end of the palpi or even a little longer than the palpi. The palpi are longer than broad. The RhipicephalÆ have short palpi, nearly or quite as broad as long, more or less conical or subtriangular. They were called Conipalpi by Canestrini.
Synopsis of Genera.
Genus. Ixodes, Latreille.
Ixodes reduvius, L., 1758.338
Syn.: Acarus reduvius and ricinus, L.; Ixodes ricinus, Latreille, 1806.
The males are oval; their length 1·2 to 2mm.; they are brownish-red or black in colour; the females are yellowish-red, 4mm. long;
The dog tick (fig.360) lives in thickets on leaves, etc., and attacks sheep and oxen, and more rarely dogs, horses, and human beings, into the skin of which the female bores with the rostrum in order to suck blood; the bite is not dangerous, and sometimes is not even felt. Inflammation, however, is set up if the creatures are forcibly removed from the wound, as the rostrum as a rule is torn off in the process. If left alone or smeared over with some grease—vaseline, oil, butter, etc.—the creatures drop off spontaneously. Sometimes the entire tick bores itself into the skin; they also appear to be permanent inmates of kennels.
Fig. 359.—A., the rostrum of Ixodes ricinus (male); B>., the terminal joint of the maxillary palpi of the female. Enlarged. (After Pagenstecher.)
Fig. 360.—Female of Ixodes ricinus, gorged full, dorsal and ventral surfaces. 2/1. (After Pagenstecher.)
[The species I. reduvius is the same as I. ricinus, Latreille. The male is 2·35 to 2·80mm. long; the body is dark brown, almost black, with a pale, almost white, margin; there are also traces of reddish mottling. CoxÆ of the first pair of legs with a short spine. Rostrum much shorter than that of the female; shield oval; anal shield small, about one-third the length of ventral shield. The adult female varies from 2·80 to 3·5mm. when not distended, but when gorged may reach 10mm. long. The shield and legs are dark blackish-brown, body deep orange-red with four dark longitudinal lines, paler beneath and light grey in front. When distending it is pale red to grey or white; when fully gorged olive-green, or dark red to black, with irregular yellow streaks on the back and sides just before egg-laying. Sexual orifice opposite fourth pair of legs. The nymph varies from 1·60 to 1·70mm. long when fasting; the body is olive-white, opaque, with four distinct brown posterior markings and similar anterior ones, leaving a pale centre to the shield. When fully gorged it is 3mm. long. As the nymph distends, it changes from opaque white to blue-black, and finally black. The little larva is 0·80 to 1·50mm. long, transparent with olive-green intestinal markings; as it becomes inflated it changes to blue-black, and then black. There are no eyes. It is widely distributed, and chiefly attacks sheep; sometimes it occurs on dogs and also attacks
[Synonyms.—Considerable confusion exists over the name of this and other common ticks, owing to the same species having been described under a great many names. Observers have taken the same species on different animals and in various stages to be distinct, and have described them accordingly.
[The name Ixodes reduvius, Leach, does not stand, as Leach was describing quite a different parasite. The name I. ricinus, Latreille, 1806, is now substituted by Neumann and Wheler.
[The synonyms given by Wheler are as follow: Reduvius, Charleton, 1668; Ricinus caninus, Ray, 1710; Acarus ricinoides, de Geer, 1778; Acarus ricinus, LinnÆus, 1788; CynorhÆstes reduvius, Hermann, 1804; CynorhÆstes ricinus, Hermann, 1804; Ixodes megathyreus, Leach, 1815; Ixodes bipunctatus, Risso, 1826; CynorhÆstes hermanni, Risso, 1826; Crotonus ricinus, Dumeril, 1829; Ixodes trabeatus, Audouin, 1832; Ixodes plumbeus, DugÉs, 1834; Ixodes reduvius, Hahn, 1834; Ixodes fuscus, Koch, 1835 (?); Ixodes lacertÆ, Koch, 1835 (?); Ixodes pustularum, Lucas, 1866; Ixodes fodiens, Murray, 1877; Ixodes rufus, Ixodes sulcatus, and Ixodes sciuri, Koch.—F.V.T.]
Ixodes holocyclus, Neumann, 1899.
[Under the name I. holocyclus, Cleland (Journ. Trop. Med. and Hyg., 1913, xvi, No. 3, pp.43–45) says that: “This tick is common in man where there is dense scrub and tropical jungle along the east coast of Australia at certain times of the year. It may cause severe symptoms in children resulting in death.” He records a child being attacked in 1884 which died, and another case from which 200 ticks were removed, the symptoms being weak heart, collapse, syncope, but the patient recovered under treatment; again, in the same journal (pp.188, 189), the case of a 4 12-year-old girl who was bitten showed widespread muscular paralysis, and other cases resembling conium poison.
[Taylor (Rep. Ent. Aust. Inst. Trop. Med., 1911, p.21, 1913) refers to this species as the scrub tick of New South Wales. The partially fed female has a dark reddish-yellow scutum and is almost as broad as long, punctations very numerous, equal and confluent in places, long white hairs on the lower half of each coxa. He records it as attacking man commonly, mentioning Kamerunga, Cairns district, Queensland, and Sydney, N.S.W., as localities.—F.V.T.]
Ixodes hexagonus, Leach, 1815.
Syn.: Ixodes sexpunctatus, Koch, 1897; I. vulpis, Pagenstecher, 1861.
Lives in the same manner as the foregoing; especially attacks hounds, but also other mammals and even birds. The difference consists in the shape of the legs, the shorter rostrum, and the larger size of the male. It also occasionally attacks man, but is usually confused with the previously mentioned species.
[The synonyms of this species are as follow:339 Ixodes autumnalis, Leach, 1815; I. erinacei, Audouin, 1832; I. reduvius, Audouin, 1832; I. crenulatus, Koch; I. erinaceus, Murray, 1877; I. ricinus, MÉgnin, 1880. Two other synonyms are given above by Braun.
[The female when fully replete is 11mm. long, when fasting 3·86mm.; the shield is heart-shaped and punctate, body finely hairy; palpi short and broad; labium shorter, and tarsi of all the legs more truncate than in I. ricinus. The colour of the distended body is drab and somewhat waxy; rostrum, shield and legs light testaceous. The male varies from 3·5 to 4·0mm. long, and is reddish-brown in colour with lighter legs; the shield is punctate and leaves a narrow margin around the body; the body is elliptical, almost as large in front as behind. There is a spine on the coxÆ of the first pair of legs, which is shorter than in the male I. ricinus and longer than in the female. The genital orifice is opposite the interval between the second and third pair of legs. The fasting nymph is 1·76mm. long, light bluish-grey, margined and transparent, with four large posterior intestinal marks joined together behind the shield and smaller ones extending to the front and sides. When fully distended it is uniformly brownish-white; shield, legs and rostrum pale testaceous. The larva varies from 0·88mm. when fasting to 1·76mm. when gorged. Its body is light, but gradually becomes darker, with similar intestinal marks to ricinus.
[This tick is very common, especially on ferrets, stoats and hedgehogs. It is also found on sheep, cattle, etc. The males do not generally occur in company with the females on the host. Pairing probably takes place on the ground.—F.V.T.]
Genus. Amblyomma, Koch.
Amblyomma cayennense, Koch, 1844.
Syn.: Amblyomma mixtum, Koch, 1844; Ixodes herrerÆ, DugÉs, 1887; Amblyomma sculptum, Berlese, 1888.
Characterized by the possession of eyes. The male measures 3·8mm. in length by 3mm. in breadth; the female 4mm. in length by 3mm. in breadth, but when full of blood may become
[This species was described by Fabricius. It occurs in Cayenne, Guiana, in Southern Texas, Florida, California, Mexico, Guatemala, Honduras, Nicaragua, Costa Rica, Panama, Bermuda, Cuba, Jamaica, Trinidad, Colombia, Venezuela, French Guiana, Brazil, Paraguay and the Argentine. It is called the silver tick. It frequently attacks man. Schwarz and Bishopp (Bull. 105, U.S. Dept. Agric., p.158) heard of one man whose legs were well covered with suppurating sores and who was ill from the attack of these ticks and the wounds produced by scratching, and records other cases of their swarming on man. Newstead (Ann. Trop. Med. and Par., 1909, iii, No. 4, p.442) records it as the worst pest to man in Jamaica.—F.V.T.J
Amblyomma americana, LinnÆus.
The so-called long star tick, from the silvery spot on the apex of the scutum of the female. It will attack any mammal and even birds and also man. It occurs in North America, and also in Brazil, Guiana and Guatemala. Its punctures frequently end in suppuration. In the Eastern and Southern States man is more frequently attacked by this species than any other. Moss-gatherers in Louisiana are badly attacked by it.341 It also attacks the milkers in dairies. Attempts to transmit Texas fever failed with this species.
Amblyomma maculatum, Koch.
The so-called Gulf Coast tick, of the Gulf Coast, occurs on birds, mammals and man, especially cattle, and attacks the ears.
Genus. Hyalomma, Koch.
Hyalomma Ægyptium, L., 1758.
Syn.: Acarus Ægyptius, L., 1758; Ixodes camelinus, Fischer, 1823.
A species frequently found in Africa, particularly in Egypt and Algeria, and which also occurs in France and Italy, as well as in Asia. Male 8mm. in length, 4·5mm. in breadth. Female up to 24mm. in length and 15mm. in breadth. It infests large and small animals as well as human beings.342
[This is one of the largest ticks, nearly reaching the size of the bont tick. It is known in Africa as the bont leg-tick; all farm stock
Genus. HÆmaphysalis, Koch.
HÆmaphysalis punctata, Canestrini and Fanzago, 1877–1878.
Syn.: HÆmaphysalis sulcata, Canestrini and Fanzago, 1877–1878; Rhicocephalus expositicius, Koch, 1877; HÆmaphysalis peregrinus, Cambridge, 1889; Herpetobia sulcata, Canestrini, 1890.
[This species does not appear to be common. It occurs on sheep, goats, horses and cattle. I have seen a female taken from man in Britain. The female when fasting is 3·44mm. long, when gorged 12mm. long. Colour, reddish-brown, leaden-grey when gorged; dorsal shield deeply indented in front; rostrum, shield and legs brownish; body finely punctate, both above and below; sexual opening opposite the coxÆ of the second pair of legs in both sexes. Palpi a little longer than the labium; first segment short and narrow, second and third widened on the dorsal face. CoxÆ with a short, broad blunt spine; tarsi short, terminated with a spur on the first pair. The male is 3·10mm. long. Body rather narrow, yellowish to reddish-brown; dorsal shield nearly covers the whole body; numerous punctures over the whole surface. Eleven indentations on the posterior margin of the body; peritremes lighter in colour, large and comma-shaped. The three anterior pairs of legs with a short spine on the haunches, the fourth with a very long one directed backwards. The nymph varies from 2·5 to 3·0mm., is oval, and light yellow to dark red in colour. Dorsal shield rounded with few punctations. No spur on tarsi, and sexual orifice nearly obsolete. Larva short and oval. Length 1·20 mm.—F.V.T.]
Genus. Dermacentor, Koch.
Dermacentor reticulatus, Fabricius, 1794.
Syn.: Acarus reticulatus, Fabr., 1794; Ixodes reticulatus, Latreille, 1806; I. marmoratus, Risso, 1826.
This tick is provided with eyes, but it is distinguished from Ixodes and analogous genera by the lack of the abdominal plastron in the male, which measures 5 to 6mm. in length by 3·5mm. in breadth. The female may attain 16mm. in length and 10mm. in breadth. It is found in the South of Europe, in Asia, and in America; it attacks chiefly oxen, sheep and goats, and occasionally man.343
[This tick sometimes causes much annoyance to human beings. It was once most troublesome at Revelstoke. Specimens have recently been found on fowls, turkeys and pheasants in Kent.
[Other synonyms are as follows: CynorhÆstes pictus, Hermann, 1804; Crotonus variegatus, Dumeril, 1829; I. pictus, Gervais, 1844; Dermacentor albicollis, Koch, 1844–1847; D. pardalinus, Koch, 1844–1847; D. ferrugineus, Koch, 1844–1847; Ixodes holsatus, Kolenati, 1857; Pseudixodes-holsatus, Haller, 1882; HÆmaphysalis marmorata, Berlese, 1887.
[The female when fasting is 3·86mm. long by 2mm. wide. The body is depressed, larger behind and reddish-brown in colour. The shield is very large and extends to the level of the third pair of legs, with a few large and many small punctations, milky white, variegated with reddish-brown. Sexual orifice opposite the coxÆ of the second pair of legs. CoxÆ of the front legs are deeply bifid, the others with a moderate spine. When gorged light brown, and may reach 16mm. When depositing eggs the female is mottled with dark brown above and below. The male is like the female. The shield is reddish-brown, variegated with a milky white pattern. CoxÆ of the fourth pair of legs three times the size of the third. There is a sharp backwardly pointing spine on the second palpal segment, also seen (but smaller) in the female. Length 4·20mm.
[According to Mr. Wheler this is a very variable species both in size and colour. It occurs in England on sheep, but not commonly. It has probably been introduced into Britain. Besides the animals mentioned above it is also found on deer.—F.V.T.]
Dermacentor venustus, Banks.
[The Rocky Mountain tick fever tick. This species has been wrongly called Dermatocentor reticulatus var. occidentalis. The correct name of the carrier of Rocky Mountain tick fever is Dermacentor venustus, Banks (Hooker, Bishopp and Wood, Bull. 106, U.S. Dept. Agric., Div. Ent., p.165).
[The female is from 13·8 by 10 by 6·4mm. to 16·5 by 11·4 by 6·9mm. when gorged; the male from 2·1 by 1·5mm. to 6 by 3·7 by 1·4mm. The male reddish-brown; scutum with an extensive pattern of white lines, usually but little white on the mid-posterior region, legs slightly lighter than scutum, joints tipped with white. Female with scutum mostly covered with white, abdomen reddish-brown, legs as in male. The nymph when unengorged reddish-brown, when gorged dark bluish-grey; the larva is yellowish-brown when unengorged, slate blue when engorged. The ova light brown, shiny and smooth.
[The chief wild hosts are the brown bear, coyote, woodchuck, rabbit, wild cat, badger and mountain goat for the larvÆ; practically all small mammals act as hosts for larvÆ and nymphÆ, whilst the adults are seldom found on other than large domestic animals; horses and cattle are preferred. It occurs in British Columbia, southward to Northern New Mexico, and from the foothills of the Rocky Mountains in Colorado to the base of the Cascade Range in Oregon and California; abundant in Western Montana, Idaho, Eastern Washington, Oregon, North Utah, West Wyoming and North-west Colorado.
[Of great importance in the Bitter Root Valley of Montana, where a number of cases of fever occur each year, with a mortality of about 70 per cent. In British Columbia this tick causes tick paralysis in man and sheep. Only the adults seem to attack man and animals there (Hadwen and Nuttall, Parasitology, 1913, vi, No. 3, pp.288–297 and 298–301) according to the Canadian Medical Association Journal, December, 1912. The symptoms are unlike spotted fever. For full details of this tick vide Bulls. 105 and 106, U.S. Dept. Agric.]
Dermacentor occidentalis, Neumann.
This tick only occurs in the Pacific Coast region of the United States. Owing to the fact that it frequently attacks man as well as occurring in great abundance in Oregon and California, it is of considerable economic importance. It is spoken of as the wood tick, and in the regions where found is the most common tick to attack man. Hooker, Bishopp and Wood (Bull. 106, U.S. Dept. Agric., Div. Ent., 1912, p.189) state that a number of cases have been brought to their notice where the bite of this tick has caused considerable local inflammation, which in some cases required physicians’ attention. It has been supposed to be connected with Rocky Mountain spotted fever, but it is doubtful if it is concerned in its transmission. The engorged female is steel grey, the dorsum with an olive-green surface colour, which covers the grey except in small spots, giving a mottled appearance. The unengorged males and females are reddish-brown, scutum covered with a whitish bloom, interrupted by many red punctures. The female is 9 by 6·1 by 3·3mm. to 11·8 by 7·6 by 5·6mm.; the male 2·8 by 1·6mm. to 4·2 by 2·3mm. The larvÆ are bluish-grey when engorged, reddish-brown when unengorged. The nymph is light brown, sides of scutum darker, and the intestines dark brown. It is confined to the Coast Range and Sierra Nevada Mountains in California and Oregon and the small mountain range to the south-west.
Dermacentor variabilis, Say.
The American dog tick has also been found on man, but it is of little economic importance as it is easily removed from its host.
Genus. Margaropus, Karsch.
Margaropus annulatus australis, Fuller.
The so-called Australian cattle tick. Newstead344 reports this as a great pest to man in Jamaica in its larval stage. Its chief hosts are cattle, horses, goats, sheep, dogs and rabbits.
Margaropus microplus, Canestrini.
Recorded by AragÃo (Mem. Inst. Oswaldo Cruz, 1911, iii, fasc. 2, p. 163) as occurring in larval stage on man in Brazil.
Genus. Rhipicephalus, Koch.
Rhipicephalus sanguineus, Latreille, 1804.
Syn.: Ixodes sanguineus, Latr., 1804; I. rufus, Koch, 1844; Rhipicephalus limbatus, Koch, 1844; Rh. siculus, Koch, 1844; Rh. stigmaticus, GerstÄcker, 1873.
Spread over almost the entire tropical and sub-tropical regions, occurring in Europe in the South of France and in Italy; it infests dogs and more rarely sheep; oxen, cats, foxes and human beings are also attacked.345
Neumann’s Table of Species of Argas.
| 1 | Body elliptical (sides curved) | 2. | |
| Body oblong (sides straight), ending anteriorly in a point | 7. | ||
| 2 | Body transversely oval | vespertilionis. | |
| Body elongate oval | 3. | ||
| 3 | Margin of body striated | 4. | |
| Margin of body formed by quadrangular areolÆ | PERSICUS. | ||
| 4 | Body flat, integument plainly wrinkled | 5. | |
| Body tumid, elongate; integument finely wrinkled; coxÆ of fourth pair of legs near anterior third of body | hermanii. | ||
| 5 | Body oval, narrowed anteriorly | REFLEXUS. | |
| Body elliptical, blunt, hardly narrowed anteriorly | 6. | ||
| 6 | Body twice as long as broad | cucumerinus. | |
| Body hardly longer than broad | transgariepinus. | ||
| 7 | Dorsal integument with large polygonal depressions; tarsi appearing bifid | BRUMPTII. | |
| Dorsal integument almost smooth; tarsi not appearing bifid | Æqualis. |
The ArgantinÆ are distinguished from the IxodinÆ by the head, which in the former is situated on the inferior aspect of the cephalothorax, while in the IxodinÆ it projects freely; also by the very short proboscis, the small club-like palpi, the lack of suckers on the legs, as well as by the scutellum, which covers the entire back and is bent up round the borders. Two genera are distinguished: Argas, Latreille, 1796 (Rhynchoprion, Hermann, 1804), and Ornithodorus, Koch, 1844. The species live on mammals, but more especially on birds.
Genus. Argas, Latreille.
Argas reflexus, Fabricius, 1794.
Syn.: Acarus reflexus, Fabricius, 1794; A. marginatus, Fabricius, 1794; Rhynchoprion columbÆ, Hermann, 1804.
Fig. 361.—Argas reflexus: from the dorsal surface, the intestine showing through the integuments. (After Pagenstecher.)
The European marginated tick, Argas reflexus (length of male 4mm., breadth 3mm., length of female 6 to 8mm., breadth 4mm.), is of a yellowish colour and has yellowish-white legs. The ingested blood shows red or brown through the intestine, which is provided with blind sacs. It lives in dovecots. It remains hidden during the day and at night crawls on to the sleeping pigeons to suck their blood. It has been observed in France, England, Italy, Germany, and Russia. Persons sleeping near infected dovecots, or in apartments formed from pigeon-lofts, are also attacked, even when the room in question has not been used for sheltering pigeons for years, as “marginated ticks” can live in a fasting condition for a very long time. The bite sometimes gives rise to serious symptoms, such as general erythema and sudden oedema.
[This pest more often feeds on the blood of man than is imagined. Blanchard states that he has received them from men’s clothes in Strasburg. Boschulte, of Westphalia, records these parasites in a bedroom inhabited by children and connected with a pigeon-house. The children were bitten during sleep on the hands and feet. The result of the bite was intense itching along the nerves, the bite only being marked by a red spot. In a girl of 14 or 15, vesicles were formed similar to those produced by burns, and in an old man an ulcer formed. Others record painful punctures and persistent oedema produced by this pigeon pest. It was once abundant in Canterbury Cathedral, and often caused much annoyance, I am told, to the worshippers; the ticks falling down from the roof, where they were living, derived from the numerous pigeons that breed in the towers. This Acarus has enormous powers of vitality, living without food for months at a time.—F.V.T.]
Argas persicus, Fischer de Waldheim, 1824.
Of oval form and brownish-red colour. The male measures 4 to 5mm. in length by 3mm. in breadth; the female 7 to 10mm. in length by 5 to 6mm. in breadth. It frequents the entire north-west
Fig. 362.—Argas persicus: ventral aspect. 7/1. (After MÉgnin.)
[This tick, sometimes called the tampan and wandlius in South Africa, is mainly a fowl parasite. Fowls and ducks frequently die under its attack, particularly young ones, death being due to loss of blood. This tick remains attached to its host during its larval stage for about five days; it then leaves and moults in concealment. In its subsequent stages it visits its host by night and remains for about an hour only, during which time it distends itself fully with blood. As a nymph it moults twice, not once as do the cattle ticks. This tick and other Argas become larger with each moult, but retain their same general appearance. The female visits the host every now and then, and, between, deposits eggs in sheltered crevices. About fifty to 120 are deposited at once. Four weeks seems a necessary period to intervene between visits to the host, and the interval may be extended to upwards of a year according to Lounsbury.346
[It is found in the Sudan, where Balfour has found granules derived from the segmentation of spirilla in their digestive tract. Fantham and Hindl have confirmed this. It has been assumed that these granules carry infection.
[This so-called Persian tick, the miana, which is such a scourge to travellers in Persia, appears to infest the huts of natives in that country. It has been sent me from Quetta, where it has invaded houses to such an extent the natives cannot live in them. The virulence of its bite is probably due to the tick transmitting fever germs from natives, probably inured, to strangers, who would be susceptible.—F.V.T.]
Argas brumpti, Neumann.
[Found in Somaliland, by Brumpt, and in the Sudan. This tick attacks man as well as wild animals and produces a painful swelling according to King,347 but as pointed out by that naturalist it probably relies on other than human food.—F.V.T.]
Argas chinche, Gervais, 1844.
This Acarus, a native of the temperate parts of Colombia, is very troublesome to man. It is probably identical with A. americanus, Packard, which infests domestic fowls and turkeys, and occasionally also cattle, and is differentiated from A. reflexus by the sculpturing of the cuticle.
Genus. Ornithodorus, Koch.
Neumann’s Synopsis of the Genus Ornithodorus is as follows:—
| 1 | Hypostome unarmed; integument in nymph stage and partly in adult spinulose | MÉGNINI. | |
| Hypostome armed with recurved teeth; integument not spinulose | 2. | ||
| 2 | Camerostome with movable lateral flaps | TALAJE. | |
| Camerostome without movable lateral flaps | 3. | ||
| 3 | Anterior border of distal segments of legs with tubercles or festoons | 4. | |
| Anterior border of segments of legs without tubercles or festoons | 8. | ||
| 4 | Body not much contracted anteriorly | 5. | |
| Body pointed anteriorly | 7. | ||
| 5 | Tubercles of distal segments of legs higher than broad, distant | 6. | |
| Festoons of distal segments of legs as broad as high, contiguous | pavimentosus. | ||
| 6 | Eyes present | SAVIGNYI. | |
| No eyes | MOUBATA. | ||
| 7 | Eyes present | coriaceus. | |
| No eyes | TURICATA. | ||
| 8 | Integument with fine radiating wrinkles | lahorensis. | |
| Integument granular | 9. | ||
| 9 | Tarsi appearing bifid at apex | furcosus. | |
| Tarsi not appearing bifid at apex | 10. | ||
| 10 | Tarsi of first pair of legs with three dorsal tubercles, of other legs with one | canestrinii. | |
| Tarsi without dorsal tubercles or with only one | 11. | ||
| 11 | Tarsi of last three pairs of legs with pronounced dorsal protuberance | tholozanii. | |
| Tarsi of legs with indistinct dorsal protuberance | erraticus. |
Ornithodorus moubata, Murray, 1877.
An abundant African tick which is one of the carriers of the spirillum of African relapsing fever and can also carry Filaria perstans (Christy). Its body is oval, yellowish-brown when young, greenish-brown when mature. The integument is covered with mamillose tubercles. No eyes and the stout legs granular above, the tibiÆ and tarsi fringed with tubercles on the upper side. Pocock348 records it from
The female tick infected with the spirillum transmits the infection to the eggs and the next generation. They appear to be able to live without food a long time, and probably live for years. They lay their eggs in masses on the ground or in crevices, and when they hatch they are in the nymph stage with four pairs of legs. O. moubata also occurs in Madagascar with recurrent fever (Lamoureux, Bull. Soc. Path, exot., 1913, vi, No. 3, pp.146–149).
Ornithodorus savignyi, Audouin, 1827.
At one time considered the same as the preceding species, but can be easily separated by the presence of two pairs of eyes. It is widely spread over Africa and has been found in South India and at Aden. In the Sudan it occurs in large numbers. King349 records that a few miles N.N.E. of Khartoum 370 specimens were collected in two hours under a single tree by a well. It is found in Somaliland, where relapsing fever occurs and no O. moubata, which it probably replaces as a transmitter (Drake-Brockman, “Rep. Col. Office,” April 6 and April 16, 1913). It also occurs in Tunis, where the natives call it “tobbiah” (Weiss, Arch. de l’Inst. Pasteur de Tunis, 1912, pt. 4, p. 226).
Ornithodorus coriaceus, Koch.
Found in Mexico, Paraguay and California. Attacks man.
Ornithodorus talaje, Guerin, 1849.
An eyeless species with somewhat elongate pentagonal body found in Mexico and South America, called the “chinche.” A variety of it (coniceps) is found at Venice, etc., and another variety on various islands in the Indian Ocean and South Atlantic. Its bite is very painful to man.
Ornithodorus turicata, DugÈs, 1876.
Without eyes. Indigenous in Central America; attacks human beings and pigs. The bite is painful and is often followed by serious consequences.
[So virulent is this species that pigs put in an infested sty often die in a night. This “turicatas” of Mexico often reaches 6mm. in length.—F.V.T.]
Ornithodorus tholozani, LaboulbÈne and MÉgnin, 1882.
Syn.: Argas tholozani, Lab. and MÉg., 1882.
Without eyes. Males 4 to 6mm. in length and 2 to 4mm. in breadth; females 8 to 10mm. in length and 4 to 5mm. in breadth. It especially attacks sheep. Native of Persia and Asia Minor.
[This species is reputed as being very dangerous to man. It is locally know as the kÉnÉ, or sheep-bug. In its fully gorged state it is deep violet.—F.V.T.]
Ornithodorus mÉgnini, DugÈs, 1883.
Syn.: Argas mÉgnini, DugÈs, 1883.
Length 8·5mm., breadth 5·5mm. Native of Mexico.
[Another synonym for this species is Rhynchoprion spinosum, Marx. The adult males and females are grey to dark brown, the male somewhat the smaller; female 5 by 3·5 by 2·5mm. to 10 by 6 by 3·5mm. The larvÆ at the seed tick stage are dark grey, turning to pink, then to a whitish grey when engorged. The nymph when young is blood-red in front, rest pearly white; later they turn reddish-brown.
[Intense pain may be caused by its presence in and around the ears.
[Two specimens in the nymphal state were taken from the ears of a visitor to Cambridge by Dr. J. Christian Simpson. They were supposed to have entered the ears when the gentleman was camping out in Arizona (Lancet, 1901, i, No. 4,052, p.1198, fig.3).
[This species attacks the horse, ass, dog, cats and oxen, generally around the ears, and also attacks man. It is well known in the United States as infesting the ears of children (New York Ent. Soc. Journ., 1893, pp.49–52).
[It occurs in Texas, Arizona, New Mexico and California as well as Mexico, Brazil, and possibly many parts of South America; and recently Bedford (“Sec. Report Div. Vet. Res., S. African Union,” 1912, pp.343, 344) has shown it to occur at Vryburg and Fauresmith, in the Transvaal, on stock. It also occurs in the Sudan.—F.V.T.]
Other Literature on IxodidÆ.
(1) “PÉnÉtration de l’Ixodes ricinus sous la peau de l’homme,” Compt. rend. Soc. de Biol., 1891, xliii, ser. 9, iii, pp.689–691, R. Blanchard.
(2) “Notas sobre Ixodidas brazileiros,” Mem. Inst. Oswaldo Cruz, 1911, iii, fasc. 2, pp. 145–195, pls. 11 and 12, Dr. H. de Beaurepaire AragÃo. Table of Brazilian Species.
(3) “ContribuicÃo para a sistematica e biolojia dos Ixodidas,” Mem. Inst. Oswaldo Cruz, 1912, iv, fasc. 1, pp.96–120, pls. 2 and 3, Dr. H. de Beaurepaire AragÃo.
Family. TyroglyphidÆ.
Very small mites without eyes and without tracheÆ, with smooth skin.
The males usually have a suctorial pore on either side of the anus, which is used during copulation, or suckers may be found in both sexes near the sexual orifice. The mouth parts form a cone with chelate chelicerÆ, and three-jointed pedipalpi; the legs are usually short, have five segments with a terminal claw and suckers, or either one or other of these organs. The numerous species and genera live free and from choice in slowly decomposing vegetable and animal matter (cheese, cereals, flour, sugar, preserves, dried anatomical preparations, bacon, dried fruits and fungi), also in the corners of dwellings, etc.; they incidentally get into or on to man, or are found in chamber utensils and in spittoons; actual parasites are rarely found amongst them.
[The chief genera are Tyroglyphus, Rhizoglyphus, Glyciphagus, Aleurobius and Histiogaster. The first three have typical characters referred to, but are distinguished from each other by the two former having the hairs on the dorsum smooth, whilst in Glyciphagus they are hairy, plumose, or feathered. Rhizoglyphus can be told from Tyroglyphus by having claws on the tarsi without any suckers; Tyroglyphus has both claws and suckers. The larvÆ are hexapod and may become adult in the usual way by repeated moults, or they enter the so-called hypopial stage. In this the eight-legged nymph becomes quiescent, and during this stage it fixes itself to some insect or other animal by a patch of suckers on the lower surface of the hind end of the body, and is so carried from place to place. The hypopus does not feed and has a hard shell and short legs. When it has reached a new home it moults and development proceeds in the normal way. Canestrini and Kramer treat the TyroglyphidÆ as a sub-family of the SarcoptidÆ, calling them sub-family TyroglyphinÆ, the other sub-families being SarcoptinÆ, CanestriniinÆ and AnalsinÆ.—F.V.T.]
Sub-family. TyroglyphinÆ.
Genus. Aleurobius, Canestrini.
Aleurobius (Tyroglyphus) farinÆ, de Geer (part), Koch.
The male measures 0·33mm. in length by 0·16mm. in breadth; the female 0·6mm. in length by 0·3mm. in breadth. These mites possess five pairs of suctorial organs of a light colour; the legs are reddish. Moniez observed them in Lille on the skin of labourers who had been unloading Russian corn. A few of the species generally mentioned under the designation of Tyroglyphus siro are probably the common flour-mite, which also occurs on dry cheese.
[The farinÆ of de Geer is an Aleurobius described by him in 1778 (“MÉm. Hist. Ins.,” vii, t. 5, f. 15, p.97) as Acarus farinÆ.—F.V.T.]
Genus. Tyroglyphus, Latreille.
Tyroglyphus siro, L., 1756.
(Defined by Gervais, 1844.)
Male 0·5mm. in length by 0·25mm. in breadth; female 0·53mm. in length by 0·28mm. in breadth; the males have two suckers on the tarsi of the fourth pair of legs. Penis straight, colour whitish or reddish.
Tyroglyphus longior, Gervais, 1844.
White or yellowish, with two black spots on the abdomen. Male 0·55mm. in length, 0·28mm. in breadth; penis bent. Female 0·61mm. in length and 0·28mm. in breadth.
T. siro and T. longior live on dry cheese, in flour, on dried fruits, etc., and have been occasionally observed in the stools, urine, or pus of human beings, and also on their skin. The so-called vanillismus is to be attributed to these species.
[T. siro and T. farinÆ of Schrank (non Geer) are the same. They are described under other names, such as Acarus lactis, Linn.; A. favorum, Herm., etc.; A. lactis in milk, farinÆ in flour, and siro in cheese; and as A. dysenteriÆ, LinnÆus (“Syst. Nat.,” ed. 12, pp. 1024–1767).]
Fig. 363.—Tyroglyphus farinÆ: male. Enlarged. (After Berlese.)
Fig. 364.—Tyroglyphus longior, Gerv. (After Fum. and Robin.)
It is to these species that a case of dysentery was referred. Rolander, who studied under LinnÆus, was attacked by what was called dysentery. The complaint soon gave way to treatment, but eight days after it returned, soon disappeared, but again came a third time. All the time Rolander had been living like the other inmates of the house, who all escaped. LinnÆus, aware that Bartholemy had attributed dysentery to insects which he said he had seen, advised his student to examine his stool. The result was that innumerable mites were found to be present. Their presence was easily accounted for by the fact that they were found in numbers in a cup made of juniper wood from which the student alone drank of a night, and they were found to be of the same species. What this species is we do not know. LinnÆus called it Acarus dysenteriÆ, but it was the same as his Acarus siro. No records have
[Tyroglyphus minor var. Castellani, Hirst,
causes the copra itch in persons employed in the copra mills in Ceylon. The skin of the hands, arms, legs and even body becomes covered with pruriginous papules, papulo-pustules and pustules near the head. The eruption begins as a rule on the hands. The mites live in the copra dust. They produce dermatitis. Castellani produced the disease experimentally by rubbing copra dust containing mites on the skin of healthy people. Beta-naphthol ointment (5 to 10 per cent.) proved useful in treatment (Journ. Trop. Med. and Hyg., December 16, 1912, Castellani and Hirst).—F.V.T.]
Genus. Glyciphagus, Hering, 1838.
Glyciphagus prunorum, Her., and G. domesticus, de Geer.
The Glyciphagi are differentiated from the Tyroglyphi in that the chitinous hairs on the body are fringed or feathered, and that they lack a furrow dividing the cephalothorax from the abdomen. They live under similar conditions to the Tyroglyphi and are occasionally found on man or in fÆces.
[Sugar merchants and grocers are frequently troubled by swarms of G. domesticus, which leave the stores when being handled, and especially shopmen, who handle sugar kept in small stores for some time. These are the Acari that cause that irritating temporary affection known as “grocer’s itch.”—F.V.T.]
Glyciphagus cursor, Gervais.
Under this name Signor Moriggia figures a horny excrescence of great length growing from a woman’s hand, and containing in its cavities quantities of Acarus. This species is really G. domesticus, de Geer. G. domesticus has also been described by Gervais (Ann. Sci. Nat., 1841, ser. 2, xv, p.8) as G. hippopodes.
Glyciphagus buski, Murray.350
[This is a mite found by Busk and named after him by Murray. It was taken from beneath the cuticle of the sole of the foot of a negro in the Seamen’s Hospital Ship on the Thames in 1841, in large sores of a peculiar character confined to the soles of the
[From Busk’s original figure I see no reason to doubt that this is a Glyciphagus.—F.V.T.]
Genus. Rhizoglyphus, ClaparÈde, 1869.
Rhizoglyphus parasiticus, Dalgetty, 1901.
The Rhizoglyphii are to be recognized by their short legs, which are beset with spines, and by the tarsi, which terminate in a claw. They live on plants, roots and bulbs, especially the bulbs of lilies.
Fig. 365.—Rhizoglyphus parasiticus. a., male; b., female. Enlarged. (After Dalgetty.)
This species has been observed on the feet of Indian coolies working in the tea plantations; they produce a skin disease which always commences with blebs between the toes, and which almost always extends to the malleoli, but not beyond. The
Genus. Histiogaster, Berlese, 1883.
Histiogaster (entomophagus?) spermaticus, Trouessart, 1900.
The genus Histiogaster, which also approaches the TyroglyphinÆ, is characterized by the circumstance that the males possess suctorial pores used in copulation, as well as leaf-shaped appendages at the posterior end of the body. They feed on vegetables, especially on small fungi.
Fig. 366.—Histiogaster (entomophagus?) spermaticus: on left, male; on right, female—both from the abdominal aspect. 200/1. (After E. Trouessart.)
This species has been described by Trouessart,352 who found numerous specimens, some adult, others in the developmental stage (larvÆ, nymphs), and ova, in the fluid removed by puncture from
It would here rather appear to be the case of a facultative parasitism of an otherwise free-living species. Histiogaster entomophagus, LaboulbÈne, is found occasionally in collections of insects feeding on larger species containing much fat; the species also occurs on dry cantharides; it appears to belong to the region of South Europe, where, however, it is widely spread.
[Entomophagus occurs all over Europe and in America. It has been described under the following names: Acarus malus, Shimer, 1868 (Trans. Illinois Hort. Soc.); Dermaleichus mali, Riley, 1873 (Rep. Ins. Missouri, v, p.87); Tyroglyphus mali, Murray, 1877 (“Eco. Ent. Apt.,” p. 275); T. corticalis, Michael, 1885 (Trans. Roy. Micros. Soc., ser. 2, v, 3, p.27, figs.1 to 14); Histiogaster corticalis, Canestrini, 1888 (Prosp. Acarof., iii, p.397); H. aleurophagus, Sicherin, 1894, Canestrini, Prosp. Acarof., vi, p.815. Trouessart’s species is evidently distinct.—F.V.T.]
Genus. Cheyletus.
Cheyletus mericourti, Lab.
Acaropsis mericourti, Moq. Tand.
[This mite has been described from three specimens found in pus which flowed from an abscess in the ear of a naval officer, produced by inflammation of the auditory passage. Where the mites came from we do not know, as they were found near the Bank of Newfoundland. This genus of Acari has enormous mandibles and a peculiar tracheal system; two ungues and appendages to the tarsi.—F.V.T.]
Family. SarcoptidÆ (Itch Mites).
Small mites without eyes and tracheÆ, and with delicate, transversely striated cuticle. The mouth parts form a cone, over which the shield-shaped upper lip protrudes; the chelicerÆ are chelate; the pedipalpi (or maxillary palpi) have three joints; the legs are short and compact, and composed of five segments; the terminal joints have pedunculated suckers (ambulacra) or a long bristle. The larvÆ are six-legged. They live on or under the skin of birds and mammals, on which they produce the skin disease known as scabies, or itch.
[The SarcoptidÆ attack the hairs, feathers or epidermis of birds, animals and man, living as permanent parasites. The punctures they produce are followed by the formation of more or less thick crusts or scabs, beneath which the mites live and breed (so called scab, mange and itch). Most are oviparous, some ovoviviparous. The eggs are minute, ovoid, with a thin semi-transparent shell. They incubate in a few days, varying from two to ten or eleven, as a rule. Generally sarcoptic
[Speaking generally, for the SarcoptidÆ there are three distinct stages in the development of the male, four in the female, as follows:—
[(1) The larva. In this stage only three pairs of legs occur.
[(2) The nymph, in which a fourth pair of legs appear, and which thus approaches the adult; but so far no sexual organs occur. Nymphs are of two sizes—the smaller being future males, the larger females.
[(3) The next stage in the female is the age of puberty, the female now being provided with a vulvo-anal slit; this so-called pubescent female is fertilized by the male. The male then dies. But the female again casts her skin and enters another stage—
[(4) The ovigerous female—the egg-laying female—which has differently modified legs.
[The rate at which these Acari breed is very great. Gerlach has found that roughly, in each Sarcopt gallery, a female produces fifteen individuals—ten females and five males—and that the progeny reproduce again in fifteen days. The table given below thus shows that one pair may produce the enormous number of 1,500,000 descendants in three months:—
| First generation after 15 days | 10 | females | 5 | males | |||
| Second | " " 30 " | 100 | " | 50 | " | ||
| Third | " " 45 " | 1,000 | " | 500 | " | ||
| Fourth | " " 60 " | 10,000 | " | 5,000 | " | ||
| Fifth | " " 75 " | 100,000 | " | 50,000 | " | ||
| Sixth | " " 90 " | 1,000,000 | " | 500,000 | " | ||
| = 1,500,000 individuals. | |||||||
[These AcarinÆ are divided into three distinct sub-families, namely the CytolichinÆ, SarcoptinÆ, CanestriniinÆ.
[The SarcoptinÆ alone interest us here, and of the nine genera the three following are the most important:—
[(1) Sarcoptes, Latreille; Eusarcoptes.
[(2) Psoroptes, Gerv.; Dermatodectes, Gerlach; Dermatocoptes, FÜrstenberg.
[(3) Chorioptes, Gerv.; Symbiotes, Gerlach; Dermatophagus, FÜrst.; Sarco-dermatocedes, Del.
[The following are the main characters of these three genera:—
[Sarcoptes—round or slightly oval; the two posterior pairs of legs being nearly or quite concealed beneath the body; the tarsi end in simple long pedicles, with ambulatory suckers.
[Psoroptes—oval; the legs are all visible outside the margin of the body; the ambulatory suckers are carried on long triangulated stalks; the male has copulatory suckers and abdominal prolongations.
[Chorioptes—oval; legs long, thick, all visible; ambulatory suckers very wide, carried at the end of simple, short pedicles.
[Sarcoptes make channels or furrows beneath the epidermis, and in these the female lays her eggs. This form of acariasis is thus difficult to cure. It is the cause of human itch (vide Sarcoptes scabiei).
[Psoroptes do not make sub-epidermic galleries; they live and breed in colonies beneath crusts or scabs formed by the changes they produce in their host’s skin. Sheep scab is a common type of disease produced by Psoroptes. This genus is of little importance as a parasite to man.
[Chorioptes live as Psoroptes; they also do not affect man. Otodectes, Can., affecting cats and dogs, and others occur, but do not affect man as far as we know at
Sub-family. SarcoptinÆ.
Genus. Sarcoptes, Latreille.
Sarcoptes scabiei, de Geer, 1778.
Syn.: Acarus scabiei, de Geer, 1778; A. psoricus, Pallas, 1760; A. siro, L., 1778; Sarcoptes exulcerans,? Linn., 1758, Nitsch, 1818; S. hominis, Raspail, 1834, and Hering, 1838; S. galei, Owen, 1853; S. communis, Delaf. et Bourg., 1862; S. scabiei var. hominis, MÉgnin, 1880.
Fig. 367.—Sarcoptes scabiei: female, dorsal aspect. 200/1. (After FÜrstenberg.)
The body is oval or nearly circular and whitish in colour, with transverse rows of striÆ partly interrupted on the back. There are transverse rows of small bristles on the dorsal surface, and groups of trichomÆ on the front, sides and back. There are chitinous hairs at the base of the legs; the two first pairs are provided with pedunculated ambulacra in both sexes, the two posterior pairs terminate each with a long bristle in the female; in the male the third pair of legs terminate in a bristle, the fourth pair with a pedunculated ambulacrum. The anus is situated at the posterior border of the dorsal surface.
At one time numerous species were differentiated, according to the form of the Acarus, the number, position and size of the hairs and spines, even according to the hosts, etc. All these characteristics, however, fluctuate so considerably that absolute differentiation is impossible; the supposed species may be regarded in the same light as MÉgnin did, as varieties. It is also hardly possible to distinguish the mite of human scabies (S. hominis) from that of a number of domestic animals (S. squamiferus). It is best, therefore, to accept one single species (S. scabiei), which may give rise to different races or castes by living in the skin of man and mammals, but can pass from one host to the other.
[Canestrini and Kramer, in their monograph of the SarcoptidÆ, enumerate eighteen distinct species of this genus, from the dog, goat,
Fig. 368.—Sarcoptes scabiei: male, ventral aspect. 200/1. (After FÜrstenberg.)
The S. scabiei of man (S. scabiei var. hominis) (length of male 0·2 to 0·3mm., and breadth 0·145 to 0·190mm.; length of female 0·33 to 0·45mm., and breadth 0·25 to 0·35mm.) lives in the tunnels that it excavates in the epidermis, and attacks by preference places with thin skin, such as between the fingers, in the bend of the elbows and knees, in the inguinal region, on the penis, on the mammÆ, but may also affect other parts. The tunnels, which vary from a few millimetres to a centimetre and more long, do not run straight, but are somewhat tortuous; the female is found at the terminal end. The tunnels contain the excrement and oval eggs (0·14mm. in length) of the parasite; the males are rarely met with, as they die off after copulation; the females die after depositing their eggs. The six-legged larvÆ hatch out after four to eight days, and after about a fortnight, during which time they change their skins three times and undergo metamorphosis, they begin themselves to burrow. Transmission from person to person rarely is effected through linen, but by direct contact (as in coitus); transmission can be artificially effected on horses, dogs and monkeys, but not on cats.
The smaller S. scabiei-crustosÆ, FÜrstenberg, is the cause of the itch that occurs chiefly in Norway; it is not certain whether this is a distinct species of itch mite.
[This is quite a distinct species, which is recorded from Germany and France. MÉgnin (Parasitology, 1880, p.165) described this as S. scabiei var. lupi. The female is 140µ long, 340µ broad; the male is 170µ long by 150µ broad. In Science (March 3, 1893, p.125) is recorded that at the Indiana Academy of Science Dr. Robert Hessler referred to “a case of that extremely rare and almost extinct form of itch
The following forms may be transmitted from DOMESTIC ANIMALS to MAN:—
(1) S. scabiei var. equi. Male, 0·2 to 0·23mm. long, 0·16 to 0·17mm. broad. Female, 0·40 to 0·42mm. long, 0·28 to 0·32mm. broad. The horse is the normal host.
(2) S. scabiei var. ovis. Male, 0·22mm. long, 0·16mm. broad. Females, 0·32 to 0·44mm. long, 0·24 to 0·36mm. broad. This mite lives on sheep, and passes over to goats and human beings; it may also be artificially transferred to horses, oxen and dogs.353
(3) S. scabiei var. caprÆ. Male, 0·24mm. long, 0·188mm. broad. Female, 0·345mm. long, 0·342mm. broad. On goats, passing from them to horse, ox, sheep, pig and man. On the latter, in contradistinction to the varieties (1) and (2), it produces a severe affection.
(4) S. scabiei var. cameli. Frequently observed in man, chiefly in Africa. A few cases have been observed in Europe; the affection induced by it is severe.
(5) S. scabiei var. aucheniÆ. Male, 0·245mm. long, 0·182mm. broad. Female, 0·34mm. long, 0·264mm. broad. It lives on the llama, and may be transmitted to man.
(6) S. scabiei var. suis. Male, 0·25 to 0·35mm. long, 0·19 to 0·3mm. broad. Female, 0·4 to 0·5mm. long, 0·3 to 0·39mm. broad. In the domestic pig and wild boar; occasionally also in man. The settlement, however, is usually of short duration.
(7) S. scabiei var. canis. Male, 0·19 to 0·23mm. long, 0·14 to 0·17mm. broad. Female, 0·29 to 0·38mm. long, 0·23 to 0·28mm. broad. In the house-dog, and also, not unusually, in human beings.
(8) and (9) S. scabiei var. vulpis and S. scabiei var. leonis of the fox and lion have likewise been observed on man.
These are all distinct species and should read as follows: S. canis, Gerl.; S. ovis, MÉgn.; S. equi, Gerl.; S. dromedarii, Gerv. (cameli, MÉgn.); S. aucheniÆ, Raill.; S. suis, Gerl.; S. vulpis, FÜrst.; S. leonis, Can.
Sarcoptes minor, FÜrstenberg, 1861.
Anus situated on the back, legs short, pedunculated ambulacra broad; living on cats (S. minor var. cati) and rabbits (S. minor var. cuniculi). In cats this mite usually lives in the cervical region, and thence spreads to the ears and head; it usually causes the death of the infected animals; it is easily transferable from cat to cat, is difficult to transmit to rabbits, but once settled on them can easily
[S. minor, FÜrstenberg, 1861 (“KrÄtzm.,” viii, p.218), comes in Railliet’s sub-genus Notoedres, 1893 (“Zool.,” ed. 2, p.660). Canestrini raised this to generic rank in 1894 (Prosp. Acarof., vi, p.724).
[There are three species: (1) N. notoedres, MÉgnin = Sarcoptes alepis, Railliet and Lucet (Compt. rend. Soc. de Biol., 1893, xlv, p.404), and Sarcoptes notoedres var. muris, MÉgnin (Parasitology, 1880, pp. 172–174). This occurs on the black and brown rats and the water-vole.
[(2) N. cati, Hering, 1838 (N. acta. ac. Leop., ii, 18, xliv, p.605, figs.9 and 10), = Sarcoptes minor, FÜrstenberg (“KrÄtzm.,” 1861, viii, p. 215). Found on the cat in Germany, France, Italy, and Britain.
[(3) N. cuniculi, Gerlach, 1857, “KrÄtzm.,” iii, figs.20, 21. It lives on the rabbit and is found in Germany and France.—F.V.T.]
Fig. 369.—Sarcoptes minor var. cati: on the left, female (lying on its abdomen); on the right, male (lying on its back). (After Railliet.)
The itch mites of domestic animals, which belong to the genera Psoroptes (= Dermatodectes = Dermatocoptes) and Chorioptes (Symbiotes = Dermatophagus), as a rule do not infest and live on man, even when artificially transmitted. It is, however, possible for this to occur. Moniez (“TraitÉ de par.,” 1896, p.559) mentions that a species of Chorioptes—probably Ch. bovis—had been found on man, as had also Demodex folliculorum. This author also includes Dermatophagoides scheremetewskyi, Bogdanoff (Bull. soc. imp. d. natural., Moscou, 1864, xxxvii, p. 341), which has repeatedly been found on man in Moscow and Leipzig (ZÜrn, Ber. d. med. Ges., Leipzig, 1877, p.38), as Chorioptes bovis.
Other References to Scabies crustosÆ AND norvegica, ETC.
(1) “Ein Fall von Scabies crustosa norvegica,” WÜrzb. med. Zeitschr., l, pp.134–139, pl. 3, H. Bamberger.
(2) “Ueber die KrÄtzmilbe (Acarus scabiei),” Notiz. a. d. Geb. d. Nat. u. Heilk., Weimar (1913), xlii (11), Oct., pp.161–166 (1834), de Blainville.
(3) “Rapport sur le ciron de la gale (Acarus scabiei),” Ann. de Mus. d’Hist. nat., 1831; Parasitology, iv, pp.213–232, de Blainville.
Family. DemodicidÆ (Mites of the Hair-follicles).
Small Acarina, elongated in worm-like fashion, with annulated abdomen, and without eyes or tracheÆ. The mouth parts consist of a suctorial proboscis and three-jointed palpi; the legs are short, and have three segments with small terminal ungues. The anus is situated on the anterior border of the abdomen; oviparous; the larvÆ have six stumpy legs. These mites live in the hair-follicles of mammals.
Genus. Demodex, Owen.
Demodex folliculorum, Simon, 1842.
Syn.: Acarus folliculorum, Sim., 1843; Demodex folliculorum, Owen, 1843; Macrogaster platypus, Miescher, 1843; Simonea folliculorum, P. Gervais, 1844; Steatozoon folliculorum, Wilson, 1847.
Fig. 370.—Demodex folliculorum of the dog. (After MÉgnin.)
As in Sarcoptes scabiei, numerous varieties of this species are known; the form parasitic on man lives in the hair-follicles, the meibomian and sebaceous glands, and hardly ever causes inconvenience; the male measures 0·3mm. in length and the female about 0·4mm. in length. The eggs 0·06 to 0·08mm. in length, 0·04 to 0·05mm. in breadth, and are thin-shelled. The creatures are always attached with the head end downwards in the parts mentioned; they are most frequent in the sebaceous glands of the face, by the nose, lips and forehead, but they may be present on the abdomen and on other parts of the body. They may occasionally obstruct the excretory gland ducts, thus causing inflammation of the gland (comedones); their agglomeration in the meibomian glands sets up inflammation of the margins of the eyelids. There are generally only a few specimens in a gland. According to some statements Demodex occurs in 50 per cent. of mankind and even in children; they survive the death of their hosts by several days.
The variety living in the dog (D. folliculorum var. canis) is smaller than the variety living in man, and produces a skin disease resembling scabies in these animals. According to ZÜrn they may also live on man; nevertheless, no other investigator has recorded a similar observation, and attempts at artificial infection have proved negative.354
[Ten distinct species of Demodex are given by Canestrini and Kramer (“Demodicidae und Sarcoptidae,” Das Tierreich, 1899, vii). The species are certainly distinct.
[The species living on the dog (D. canis, Leydig, 1844) is cosmopolitan. According to the British Medical Journal (February 22, 1913,
Order. Pentastomida.
Family. LinguatulidÆ.
Arachnida greatly altered in consequence of their parasitic manner of life; for a long time they were regarded as helminthes. The body is elongated, vermiform, flattened or cylindrical, and more or less distinctly annulated. The head, thorax, and abdomen are not defined from each other (fig.371). The elliptical mouth, surrounded by a chitinous ring, is situated at the anterior end, on the ventral surface, and the intestine leading straight through the body opens at the posterior end. Two retractile hooks are at the sides of the mouth (fig.372); these are usually considered to be the terminal joints of two pairs of legs, but it appears to be more correct to regard them as the remains of the antennÆ and palpi (Stiles). According to this opinion, the legs in the adult state are completely degenerated.
The nervous system is reduced to an oesophageal ring. No organs of sense are recognizable except the papillÆ at the anterior end. There are neither organs of circulation nor of respiration.355
The sexes are distinct. In the small male the sexual orifice is situated ventrally in the anterior part of the body; in the female it is placed near the anus. The LinguatulidÆ lay eggs, and from each egg, after being conveyed into an intermediate host, a four-legged larva, with rudimentary mouth parts, hatches out. It goes through a series of metamorphoses, and passes through a second larval condition, which, however, possesses the essential characteristics of the fully developed form. Sooner or later it migrates during this stage, and reaches its final host, mammal or reptile, in the nostrils or lungs of which the adult LinguatulidÆ live.
[As adults they live as internal blood feeders in various birds, reptiles and mammals, especially in the nasal and respiratory passages. The larval stage occurs in another host in an encysted condition; this host is usually an animal preyed upon by the species in which the sexual forms are found. The larvÆ bore through the walls of the host’s stomach and enter liver and spleen or brain, where they encyst; here they grow until they assume almost the appearance of the adult. These encysted larvÆ on being eaten later make their way into the nasal passages and lungs, where they mature. Both adults and larvÆ occur in man, as mentioned later.
[Three genera are recognized in this family:—
[(1) Linguatula.—Body flat, annulated. Adults live in the nasal sinus.
[(2) Porocephalus.—Body cylindrical, elongate, with often deeply cut rings. Adult in respiratory organs of snakes, larvÆ in animals and man.
[(3) Reighardia.—Cylindrical, but not ringed. Not found in humans.—F.V.T.]
Genus. Linguatula, FrÖhlich.
Linguatula rhinaria, Pilger, 1802.
Syn.: TÆnia rhinaria, Pilger, 1802; Polystoma tÆnioides, Rud., 1810; Linguatula tÆnioides, Lam., 1816; Pentastoma tÆnioides, Rud., 1819.
Fig. 371.—Linguatula rhinaria: female. Natural size.
The male is white in colour, 18 to 20mm. in length, anterior portion 3 to 4mm. in breadth, posterior part 0·5mm. in breadth. The female is of a yellowish colour, 8, 10, or 13cm. long, anterior part 8 to 10mm. and posterior part 2mm. wide. The brownish eggs can be seen in the median line. The body is elongated, rather flat, and exhibits about ninety rings or segments with crenellated borders. The hooks round the mouth are strongly curved and are articulated to a basilar support. Eggs oval, 0·09µ in length, 0·07µ in breadth.
L. rhinaria, in the adult condition, lives in the nasal cavity and frontal sinus of the dog, wolf, fox, horse, goat, and occasionally of man; it causes severe catarrh, epistaxis and suppuration.
Fig. 372.—Larva of Linguatula rhinaria (Pentastoma denticulatum). Enlarged. (After Leuckart.)
Development.—The ova, which are found in masses in the nasal mucus, already possess an embryo; they are expelled with the nasal secretion, and are swallowed by herbivorous mammals with their food, mostly by hares and rabbits, but also by sheep, goats, oxen, horses, antelopes, fallow deer, pigs, cats, and occasionally also by human beings. The young larvÆ hatch out in the stomach; they possess a thickened anterior body with rudimentary mouth parts and two pairs of limbs; the body gradually tapers to a short tail.
The larvÆ of the LinguatulidÆ bore through the intestinal wall and reach the liver, more rarely the mesenteric glands, etc.; they here become encysted and enter a sort of pupal stage in which they lose their limbs; after several moultings and gradual growth the second larval stage, having the appearance of the adult Linguatula,
Later these Linguatula larvÆ make an attempt to escape from their hosts, and this, of course, can only be effected by means of an active migration; they leave the cysts, and according to their respective positions in the abdominal or pleural cavities they reach the bronchi or the intestine, and finally pass out; they may be again sniffed up by dogs and settle in their nasal cavities. Still this outward migration does not appear to be necessary for further development. A portion of the larvÆ gain access to the nasal cavities directly through the trachea, and thus herbivorous mammals certainly become directly infected. In most cases the infection of dogs, wolves and foxes, that is, of carnivorous mammals, takes place through consuming the bodies of mammals, or parts of them, such as the liver and lungs, which are affected with the second larval form; in any case most larvÆ obtain access first to the stomach of their host, from here they make an active migration through the oesophagus to the oral and nasal cavities, in which they settle. It is possible also that
Fig. 373.—Linguatula rhinaria: on left, eggs in gelatinous covering, 110/1. On right, first larval stage. 300/1. (After M. Koch.)
L. rhinaria has been observed in man in the adult as well as in the larval condition (Pentastoma denticulatum). Zenker first called attention to the occurrence of the larva in man, having found it nine times in the liver in 168 autopsies. Heschl found it twice in Vienna in twenty autopsies, Virchow found it in WÜrzburg and Berlin, Wagner in Leipzig (10 per cent.), and Frerichs in Breslau five times in forty-seven autopsies. The parasite is much less frequent in Switzerland. According to Klebs, one case occurs in 900 autopsies, and according to Zaeslin two cases occurred in Basle to 1,914 autopsies. In the Seamen’s Hospital in Kronstadt P. denticulatum has been found six times in 659 autopsies. It was almost always the liver that contained one or a few specimens. The parasite was very rarely found in the kidney or spleen, or encysted in the intestinal wall. The adult L. rhinaria is far more rarely observed in man.
A case reported by Landon that related to a blacksmith of Elbing is particularly interesting. This man accompanied the campaign of 1870; he soon, however, fell ill with pains in the liver, accompanied by icterus and intestinal disorders. Soon after the war, and after the symptoms were reduced to icterus and weakness, bleeding of the nose set in and continued with slight intermissions for seven years; an unpleasant sensation of pressure in the left nasal cavity set in, with inflammatory swelling of the mucous membrane. At last, in the summer of 1878, when the pressure in the nose had considerably increased, a Linguatula was expelled from the nose with a violent attack of sneezing, and lived for three days longer in water. The bleeding of the nose then ceased and the patient soon recovered. There can be no doubt that the first illness was connected with the invasion in the liver of numerous larvÆ of Pentastoma, and disappeared after their encystment; one or a few of these must subsequently have found its way to the nose and settled there.
Genus. Porocephalus.
Porocephalus constrictus, v. Siebold, 1852.
Syn.: Nematoideum hominis, Diesing, 1851; Pentastomum constrictum, v. Sieb., 1852; Porocephalus constrictus, Stiles, 1893.
Porocephalus is distinguished from Linguatula by its cylindrical body and by certain internal structures. Porocephalus constrictus is at present only known in its larval stage. It is milk white in colour with golden-yellow hooklets. Number of rings, twenty-three. Length 13mm., breadth 2·2mm. There are no prickles on the posterior border of the annulations of the body.
This species was first discovered by Pruner encysted in the livers of two negroes in Cairo. Bilharz reported two further cases in which the parasites were encysted in the liver and in the mucosa of the intestine; a few other observations have been made by Fenger, Aitken, Giard and Chalmas. Aitken’s report deals with soldiers of the British Colonies in Africa. The parasites were discovered in
Pruner has found the same parasite also in the liver of the giraffe.
It has recently been assumed that Porocephalus constrictus is the larva of Pentastoma moniliforme, Diesing, 1835, that attains a length of 70mm. and lives in the lungs of African Pythonides. The larva is known to have been ejected from monkeys (Cercopithecus albogularis, Cynocephalus maimon), from the giraffe (Camelopardalis giraffa), from a species of hyÆna (Proteles cristatus), and should be expected to occur frequently in smaller mammals which have been swallowed by African serpents of enormous size.
[The three species of PentastomidÆ, or tongue worms, found in man are Linguatula serrata, FrÖlich; Porocephalus armillatus, Wyman; and Pentastoma moniliformis, Diesing.
[(1) Linguatula serrata has been referred to under a great number of names.
[It is recorded from man in Central America (Darling, Bull. Soc. Path. exot., 1912, v, p.118; and again Arch. Int. Med., 1912, v, p. 401), also from Rio de Janeiro (Mem. Inst. Oswaldo Cruz, 1913, fasc. ii, p.125) by Faria and Travassos.
[(2) Porocephalus armillatus, Wyman, is also known under a variety
[(3) Pentastoma moniliformis, Diesing,358 is an Oriental species, found in India, Indo-China and South China, and the Malay Archipelago. The adult occurs in both the Indian and reticulated pythons. The nymphal stage has been found in monkeys, the tiger, the civet and the Indian otter.
[The nymph has twice been found in man; in one case in the liver of a Filipino, the other in the serous coat of the small intestine of a native of Sumatra.
[This species can be told by the female having twenty-nine to thirty-three body rings, the male twenty-six, and the annulations are more bead-like and less prominent than in the African species.
[In addition to these three, Sambon thinks it probable that others occur in man.—F.V.T.]
Other References to PentastomidÆ.
(1) “Die Wanderung des Pentastomum denticulatum beim Rinde,” Centralbl. f. Bakt. u. Parasitenk., Jan. 2, 1889, v (1), pp.1–5, V. Bates.
(2) “Il Pentastoma moniliforme, Dies., nella pantera,” Med.-vet. Torino, 1877, 4 s., vi (12), pp.529–532, R. Bassi.
(3) “On the Organization and Development of Linguatula (Pentastoma), accompanied with the description of a new species from the abdominal cavity of the mandrill,” Ann. and Mag. Nat. Hist., 1848, 2 s. ii (7), 2, pp.69–70, v. Beneden.
(4) “De la Linguatula ferox (Pentastoma denticulatum aut serratum),” Bull. Acad. roy. d. Sci. d. Belg., 1855, xxii, pt. 1 (1), pp.4–10, v. Beneden.
(5) “Note sur quelques pentastomes,” Bull. Acad. roy. d. Sci. de Belg., 1857, 26, 2 s., ii (5), pp.29–30, v. Beneden.
(6) “Ueber das Pentastoma in de gekrÖsdrusen den Schafe,” Repert. d. Thierh. Stuttg., 1861, xxii, pp.37–38, Collin.
(7) “Eine Linguatula aus der MesenterialdrÜse des Schafes und Dromedars als zweites ungesche. Stadium von Pent. taenioides,” Notiz. u. Tagsber. u. d. Geb. d. Nat. u. Heilk. Jena, 1862, v, pp.127, 128, Colin.
B. INSECTA (Hexapoda).
Three separate regions can always be distinguished in the body of insects, namely, the head, thorax and abdomen. The HEAD is a roundish unsegmented capsule and possesses four pairs of appendages. The first pair are the various shaped feelers (antennÆ), which are placed on the superior surface of the head next to the eyes; then more ventrally placed a pair of upper jaws (mandibles) without palpi and without articulations; they are powerful masticatory organs.359 The first pair of lower jaws (maxillÆ) are jointed and bear a palpus (palpus maxillaris); the second pair of maxillÆ are soldered together and form the lower lip (labium), and likewise carry a palpus labialis on each side. The upper lip (labrum), as well as the other parts (which, however, are only appendages), belong to the mouth, which is really formed of a number of closely united pieces. The mouth parts are modified according to the functions required of them. Coleoptera, Neuroptera, and Orthoptera have biting or masticatory mouth parts which conform with the scheme described above. In the licking mouth parts of the Hymenoptera the maxillÆ and under lip are considerably elongated, while the mandibles retain their form and are used for triturating the food; in the Lepidoptera nearly all the mouth parts are shortened except the maxillÆ, which form a long and sometimes spirally rolled suctorial proboscis; the Diptera and Rhynchota have piercing and sucking mouth parts. The mandibles and maxillÆ are metamorphosed into needle-like structures, while the suctorial apparatus is formed by the labrum.
The thorax consists of three segments, which are frequently united; ventrally it carries three pairs of legs, which consist of a definite number of articulated pieces joined together. Their form also changes according to their function, so that legs for running, walking, digging, swimming, jumping, and preying are seen. A pair of wings are respectively attached to the last and last but one thoracic rings, and these may be traced back, not to metamorphosed appendages, but to tracheal branchia. They are composed of chitinous membranes supported by branched structures (veins or ribs). Their size and formation vary; they are seldom of equal size and form (Neuroptera); often the posterior wings are larger than the anterior wings, the former then only serving as protective coverings for the latter (Coleoptera), or the anterior wings are larger (Lepidoptera), or the posterior wings are shortened or are entirely absent (Diptera); and finally there are insects in which both pairs of wings are lacking.360
The abdomen retains its segmentation, but, with the exception of a few groups related to the primitive forms of insects, has no appendages in the imago condition; the abdomen usually consists of ten segments, on the last of which the anus is situated.
We need only observe the following characters in considering the anatomy of insects:—
The EPIDERMIS consists of the chitinous cuticle, which is separate from the cellular layer beneath (hypodermis); the various appendages are supported by the chitinous layer.
The INTESTINAL CANAL usually consists of the anterior, median and terminal intestine, and as a rule passes straight through the body; salivary glands discharge into the anterior part, and, in some cases, yield a stiffening secretion which serves for spinning webs; numerous or scanty hepatic tubes are appended to the median intestine, while on the border between the median and terminal intestine open four to six long tubes (vasa malpighiana), which act as urinary organs. Finally the end portion of the intestine carries various glands (anal and rectal glands, etc.).
The CENTRAL NERVOUS SYSTEM agrees in structure with that of the Annelids, but is more highly developed. The pharyngeal ring surrounds the front part of the intestine; the sensory nerves originate from its SUPERIOR PHARYNGEAL GANGLIA and are the seat of the higher psychical functions; the INFERIOR PHARYNGEAL GANGLIA govern the mouth parts, and in addition appear to regulate the movements (cerebellum) of the vertebrates.
The chain of GANGLIA lying on the ventral side of the abdomen consists primitively of pairs of ganglia corresponding with the twelve segments, which are connected by longitudinal and transverse commissures. But many changes in the ganglia may be seen in insects caused by partial or entire amalgamation of single ganglia, so that in a few cases only one abdominal ganglion is present. In conclusion, a definite INTESTINAL NERVOUS SYSTEM is always present.
Of the organs of sense the FACETTED EYES, situated at the sides of the head, deserve special mention, as do also the ORGANS OF TOUCH and SMELL, situated on the antennÆ, and the ORGANS OF HEARING and taste, or finer sensations, situated at the mouth and in the buccal cavity.
The sounds emitted by insects are, as a rule, produced by the friction or beating of certain chitinous parts, but sounds are also produced in breathing (flies).
The ORGANS OF RESPIRATION, the so-called tracheÆ, are highly developed; there are openings (stigmata) at the sides of the body which draw in air by means of the active participation of the muscles of the body. The number of stigmata varies between two and ten pairs; the tracheÆ themselves branch off from the trunks in the most varied manner, and carry air to the internal organs.
The colourless BLOOD circulates between the tissues and organs, and is kept circulating by the contraction of a chambered dorsal vessel provided with ostia, and which terminates in a short aorta opening at the anterior end.
Insects are SEXUALLY DISTINCT; their sexual glands are in pairs and have a tubular structure, but the testicular tubules are united together by a capsule into an oval testicle; exceptionally, also, the excretory canals are double, as also the sexual orifices; usually the paired canals unite into a single oviduct or spermatic duct which terminates at the posterior end of the body after receiving the products of various glands.
As to the HISTORY OF THE DEVELOPMENT of insects, all that is necessary to mention here is that the young hatched from eggs only exceptionally (as in Apterygota) resemble the adult parent (insecta ametabola); as a rule they differ from them not only in the shape of the body, but also more or less by their manner of life, and only attain the form of the parent through METAMORPHOSIS. This is a gradual process (insecta hemimetabola) in the Rhynchota and Orthoptera, or a sudden one with a stage of inanition (insecta metabola) in the other orders. This stage of rest or inanition, the PUPA, concludes the larval life (caterpillar, maggot,
The insects are divided into numerous orders according to the form of the mouth parts, the structure of the wings, as well as the manner of the development; with the exception of the lowest group (Apterygota), which is most nearly related to the ancestors of the insects, and which has no wings and undergoes no metamorphosis, all the remaining orders, which are termed Pterygota, have wings on the thorax, though there are, of course, a few species and families of this group which have lost their wings.
The Pterygota include—
(1) Orthoptera.—Biting mouth parts, anterior wings leathery, posterior wings thin, folded longitudinally; metamorphosis incomplete (grasshoppers, crickets, cockroaches).
(2) Pseudoneuroptera.—Biting mouth parts, wings of equal size, thin, not folded up (dragon-flies, hair and feather lice, termites).
(3) Rhynchota or Hemiptera.—Mouth parts formed for puncturing and sucking; wings alike, or the anterior wings may be thickened, parchment-like at their base (plant lice, cicadÆ, bugs and true lice).
(4) Neuroptera.—Biting mouth parts; wings alike, thin; metamorphosis complete (ant-lions, lace-wing flies, etc.).
(5) Trichoptera.—Licking mouth parts; anterior wings narrow, posterior wings longitudinally folded, both ornamented with little hairs; the larvÆ are worm-like in form, live in water, and breathe through tracheal gills (may flies, etc.).
(6) Lepidoptera.—Suctorial mouth parts; wings covered with scales (butterflies).
(7) Coleoptera.—Biting mouth parts; anterior wings thickened and differ in colour, appearance and function from the thin, folded posterior wings (beetles).
(8) Hymenoptera.—Mouth parts for licking and biting; the wings alike, membranous (ichneumon flies, ants, wasps, bees, humble bees).
(9) Diptera.—Mouth parts formed for puncturing, sucking or licking; posterior wings degenerated (gnats, flies, gadflies, fleas).
(10) Strepsiptera.—Anterior wings shortened; the female without wings and living parasitically (fan-wings).
The parasites of man occur amongst the Rhynchota, Coleoptera, and amongst the Diptera.
[The most usual and recent classification of the Hexapoda is the following:—
(1) Aptera.—Wingless insects; scarcely any metamorphosis.
(2) Neuroptera.—Four membranous wings, frequently with much network; the front pair not much, if at all, harder than the under pair; the latter with but little or no fan-like action in closing; mandibulate; metamorphosis variable, but rarely complete.
(3) Orthoptera.—Four wings; front pair coriaceous or leather-like, usually smaller than the other pair, which are of more delicate texture and contract in repose like a fan; mandibulate; metamorphosis complete.
(4) Thysanoptera.—Four very narrow fringed wings; mouth imperfectly suctorial; metamorphosis slight.
(5) Hemiptera.—Four wings; the front pair either all transparent or with the basal half leathery; mouth suctorial; metamorphosis slight.
(6) Diptera.—Two membranous wings only; mouth suctorial, very varied; metamorphosis complete.
(7) Lepidoptera.—Four large wings covered with scales; mouth suctorial, metamorphosis great.
(8) Hymenoptera.—Four membranous wings; front pair larger than hind, which do not fold up in repose; mandibulate, sometimes with a tubular proboscis; metamorphosis complete.
(9) Coleoptera.—Four wings, the front pair hard and horny (elytra), meeting in a line over the back and covering the delicate hind pair; mandibulate; metamorphosis complete.
[There are two other well-known arrangements, namely, Packard’s and Brauer’s, of recent date, but the one given here, which is based on Linnaeus’ grouping by Dr. Sharp, is by far the simplest.—F.V.T.]
Order. Rhyncota.361
The lower lip forms a long thin tube that can be turned back (rostrum), and within which lie the setaceous mandibles and maxillÆ; the first thoracic segment is not united with the two posterior ones; the anterior wings are usually leathery as far as the centre.
(a) Rhyncota aptera parasitica.
Family. PediculidÆ (Lice).
The lower lip is transformed into a projecting rostrum provided with barbed hooklets in which the hollow extensile sucker (maxillÆ and mandibles) is situated; no wings; no metamorphosis; only simple eyes; the antennÆ are five-jointed, the feet possess hook-like terminal structures; the barrel-shaped eggs (nits) are deposited on the hair of the host.
[The lice or PediculidÆ are also known as Anoplura and Siphunculata.
[They have been split up into a number of families and sub-families and a number of genera, but as far as this work is concerned it is best to retain the single family PediculidÆ.
[Only the three species mentioned here are common parasites of man, but now and then horse and cattle and sheep lice, HÆmatopinus, may cause transitory annoyance.—F.V.T.]
Genus. Pediculus, LinnÆus.
Pediculus capitis, de Geer, 1778.
Fig. 374.—Mouth parts of Pediculus vestimenti. Enlarged. (After Denny.)
Fig. 375.—Ovum of the head louse. 70/1.
Male 1 to 1·5mm. in length, female 1·8 to 2·0mm. in length. The colour varies from light grey to black according to the colour of the hair of the human race upon which they are parasitic. The abdomen has eight segments, of which the six central ones are
The head louse lives especially in the hairy parts of the head of human beings; more rarely it is found on other hairy parts of the body. It is spread over the entire surface of the globe, and was present in America before the arrival of Europeans. Quite exceptionally it is said that it bores itself deep into the epidermis and can live in ulcers.
[The eggs are pear-shaped and are attached to the hairs near the roots by means of a clasping collar. They hatch in about seven days. The young are like the adults and mature in a month. Its general colour varies with that of its host. In West Africans nearly black, in Hindoos dark and smoky, on Chinese and Japanese yellow, on Hottentots orange, on South American Indians dark brown (Murray).—F.V.T.]
Pediculus vestimenti, Nitzsch, 1818.
The head in front is somewhat rounded. AntennÆ longer than in the head louse; 2 to 3·5 to 4mm. in length; whitish-grey; the abdomen is broader than the thorax; stigmata as in P. capitis. Eggs 0·7 to 0·9mm. in length; about seventy are deposited.
Fig. 376.—Head louse, male. 15/1.
Fig. 377.—Pediculus vestimenti, Burm.: adult female. 15/1.
P. vestimenti lives on the neck, throat and trunk of persons, and the clothing next the body, in which also the eggs are deposited. The louse of so-called pedicular disease (P. tabescentium) is, according to Landois’ researches, only the usual P. vestimenti; moreover, many cases of phthiriasis are attributable to mites or fly maggots.
[This parasite has often been a great pest amongst soldiers during long campaigns, especially amongst the Russians during the Crimean War. Vide also notes in Addenda (p.615) under “Body, Head and Clothes Lice.”—F.V.T.]
Genus. Phthirius, Leach.
Phthirius inguinalis, Redi, 1668.
Syn.: Pediculus pubis, L.
Male 0·8 to 1·0mm. in length; female 1·12mm. in length; colour greyish-white; form subquadrate; the two posterior pairs of legs are strong; the abdomen has nine segments and six pairs of stigmata; and still another pair of stigmata is situated between the two anterior limbs. Eggs pear-shaped, 0·8 to 0·9mm. in length, 0·4 to 0·5mm. in breadth, and are deposited in rows of about ten on the hairs.
Fig. 378.—Phthirius inguinalis, Leach: they are distinguished by the larger tracheal trunks originating from the stigmata. Enlarged.
Pediculus pubis, which is found almost exclusively in the Caucasian race, lives on hairy parts of the body, but hardly ever on the skin of the head; the pubic region is its favourite place of abode.
[This species reproduces more rapidly than other lice, and is communicated much more freely. The eggs are often laid singly attached to the hairs near their apex. It is known as the “crab louse.”—F.V.T.]
(b) Rhyncota hemiptera.
Family. AcanthiadÆ.
Body flattened, antennÆ four-jointed, rostrum three-jointed, wings atrophied.
[This family, the CimicidÆ, includes the bed bugs; the proboscis, which lies in a groove, is of three segments; the front wings are shown by two small elytra, there is no trace of hind wings. Two species are known commonly to attack man.—F.V.T.]
Genus. Cimex, LinnÆus.
Cimex lectularius, LinnÆus.
Syn.: Acanthia lectularia, Fabricius, 1794.
It measures 4 to 5mm. in length, 3mm. in breadth; brownish-red; eight abdominal segments. The female deposits fifty whitish eggs at a time (1·12mm. in length) three or four times a year; the
Fig. 379.—Head of the bed bug from the ventral surface. a, the rostrum; b, the antenna; and c, the eye. 70/1.
The bed bugs live in the cracks and fissures of human habitations, under carpets, behind pictures, in furniture, bedsteads, etc.; hidden during the day, they attack persons at night to suck their blood. The alkaline secretion of the salivary glands dropped into the wound around the separate bites causes the so-called “wheals.”
The bed bugs were known in bygone days by the Greeks (?????) and the Romans (cimex). They were first mentioned from Strasburg in the eleventh century, and in England about 1500.
[This is the common bed bug of northern latitudes and must not be confused with the tropical bed bug (C. rotundatus). The bed bug can migrate from one house to another; this especially takes place when a house is uninhabited. They escape from windows and pass along walls, water-pipes and gutters, and so reach adjoining houses. This noxious pest accompanies man wherever he goes; ships and trains become infested, especially the former.
[A characteristic feature in this animal is the peculiar odour it produces, like many others in the same group of insects. This odour comes from a clear, oily volatile liquid secreted by glands in various parts of the body. Although the normal food is man’s blood, the bed bug can subsist upon moist wood, dust and dirt that collects in crevices in floors, walls, furniture, etc. The puncturing mouth consists of a fleshy under lip, within which lie four thread-like hard filaments which pierce the flesh, the blood being drawn up through the beak.
[The eggs are oval, white, with a projecting rim around one end, with a lid which is pushed off when the young hatch; they are laid in cracks and crevices in batches of from twelve to fifty. The egg stage lasts from seven to ten days. The larval stage so gradually passes into the adult that one scarcely notices the change; during its growth the skin is cast five times, and at the change the little wing-pads are seen, showing that the adult stage is reached. The young larva is at first pale yellowish-white. It resembles the parent, but has no trace of elytra. Although eleven weeks is said to be necessary for their development, the stages may be gone through much more rapidly; Howard and Marlatt362 give seven weeks in some instances. It seems pretty certain that these Cimex only take one meal of blood between each moult and another preceding egg laying.—F.V.T.]
Cimex rotundatus, Signoret, 1852.
[This bug is common in warm climates; it is an abundant insect in India, and King has found it in the Sudan, where C. lectularius is, however, the common species. It is usually known as the tropical bed bug. Signoret’s bug can be told from the other common species by the shape of the pronotum. In C. rotundatus it is uniformly convex, whilst in C. lectularius the lateral edges are flat and sometimes even concave. The abdomen of rotundatus is also rather more elongate.
[This species is of considerable importance, as according to Patton it may act partly as the intermediary host of the piroplasma of kala-azar.
[Wenyon found at Bagdad that Cimex sp. would take up Leishmania from Oriental sore, and that the parasite developed into flagellate form. Patton came to the conclusion that the bed bug transmitted Oriental sore in Cambay, India, but Wenyon contests this view (vide Journ. Lond. School Trop. Med., 1912, ii, pt. 1, pp.13–26). Franchini (Bull. Soc. Path, exot., 1912, v, No. 10, pp.817–819) was unable to connect Cimex with this disease. At present nothing seems proved. Besides their possible connection with kala-azar, it has been shown by Howard and Clark (Journ. Exp. Med., 1912, xvi, No. 6, pp.850–859) that they can carry the virus of poliomyelitis.
[This bed bug was originally described from the Island of RÉunion in 1852 by Signoret. A similar insect was described from Burma by Fieber, in 1861, as C. macrocephalus. This is the same as Signoret’s species.
[The distribution given by Patton363 is as follows: India, Burma, Assam, Malay, Aden, Islands of Mauritius and RÉunion. Patton in this paper refers to an erroneous statement made in a recent edition of this book (the last English edition). As I have personally kept lectularius in moist dirt, wood and refuse for over two years, the statement as far as I am concerned is not erroneous. Moreover, since his doubting this fact the same experiment has been twice repeated with the same results. What they did and do persist on I cannot say.—F.V.T.] whilst collecting them. It is rounder and has shorter antennÆ than
Cimex columbarius, Jenyns.
[This is common in parts of Europe in pigeon nests, and also amongst poultry (vide Report Econ. Zool. for year ending September 30, 1913, pp.142–144, Theobald). It occurs in Britain on the latter and will attack man. I have personally been badly bitten
Cimex ciliatus, Eversmann, 1841.
3·3mm. in length, yellowish-red, thickly covered with hair; indigenous in Russia (Kasan).
[From a single specimen seen it is evidently distinct.—F.V.T.]
Family. ReduviidÆ.
Head long, narrowed behind into a neck; eyes large, prominent; rostrum thick and curved; antennÆ moderately long, slender at the tip; legs long and stiff; carnivorous.
Amongst the ReduviidÆ one genus is of particular importance, namely the genus Conorhinus, which has a long head and the first segment of the beak very much shorter than the second, and the posterior tibiÆ longer than the femora.
These large bugs have a wide distribution, the Oriental region, North and South America, and the West Indies, Madagascar and West and Central Africa.
These large bugs may cause very nasty wounds by their bites, but beyond that it has recently been shown that one interposes in the life-cycle of a trypanosome, namely—
Genus. Conorhinus, Lap.
Conorhinus megistus, Burm.
This large bug has recently been shown by Chagas to be the agent in the development of the trypanosome (T. cruzii) which is the cause of the well-known disease in many parts of Brazil called Barbeiro (Barbier). This insect is about 1in. long, black, with four red spots on the pronotum, and six red lateral lines on the abdomen, black legs, head and beak. The insect is figured in a coloured plate (No. 9) in Mem. Inst. Oswaldo Cruz, 1909, i, fasc. 2, pp.158–218.
A further account is given by Neiva.364
Conorhinus sanguisuga, Lec. (Blood-sucking Cone-nose).
This bug is also known as the Texas or Mexican bed bug, also as the big bed bug. It is particularly troublesome in the Mississippi Valley in bedrooms. The bite is very severe and results in more pronounced swelling and inflammation than that of the Cimex.
The eggs of the C. sanguisuga are at first white, then become yellow, then pink; the young hatch in twenty days. There are two larval and two pupal stages, the latter showing wing-pads. The eggs are laid and the young feed out of doors, chiefly upon insects. It is particularly abundant in April and May indoors.
Conorhinus, sp. novum (Monster Bug).
Another species; acts in a very similar way in California, the bite being very poisonous.
Conorhinus rubrofasciatus, de Geer366 (Malay Bug).
This large bug attacks man in Malaysia and elsewhere. It is recorded as inflicting “a very nasty sting, which is done by the huge proboscis.” Acute pain and inflammation follow in a few minutes. In one case the whole leg became swollen. This species occurs over the whole Oriental region, in Madagascar and Sierra Leone. It is dark brown in colour with dusky yellow or brick-red markings on the pronotum and elytra. Donovan suggests that it may be connected with the kala-azar piroplasma.
Conorhinus renggeri, Herr-SchÄff
(Great Black Bug of Pampas).
This large black bug is mentioned by Darwin,367 who states as follows: “At night I experienced an attack (for it deserves no less a name) of the benchuca, a species of Reduvius, the great black bug of the Pampas. It is most disgusting to feel soft wingless insects, about an inch long, crawling over one’s body. Before sucking they are quite thin, but afterwards they become round and bloated with blood, and in this state are easily crushed. One which I caught at Iquique (for they are found in Chili and Peru) was very empty. When placed on a table, and though surrounded by people, if a finger was presented the bold insect would immediately protrude its sucker, make a charge and, if allowed, draw blood. No pain was caused by the wound. It was curious to watch its body during the action of sucking, as in less than ten minutes it changed from being flat as a wafer to a globular form. This one feast, for which the benchuca was indebted to one of the officers, kept it fat during four whole months, but after the first fortnight it was quite ready to have another suck.” Mr. Kirby368 also refers to this species.
Conorhinus variegatus (Variegated Cone-nose).
Occurs in Florida in houses, and chases bugs (Cimex) and flies; not definitely known to bite man.
Conorhinus nigrovarius.
This species occurs in South America. It is one of the forms known as bichuque. Its bite makes a troublesome swelling.
Conorhinus protractus.
also attacks man in Utah.369 It has been called the “big bed bug.”
Genus. Reduvius, etc.
Reduvius personatus, LinnÉ.
Syn.: Reduvius personatus, Leconte, 1855.
European, but also found in the United States. The bite causes intense pain. It bites when caught or handled, but does not seem to do so voluntarily. Swelling and irritation result which may last a week, and may even cause death.370 In 1899 it was very abundant
A popular name for this bug is the wheel or masked bug—a black insect, three-fourths of an inch long. The larva of this bug is carnivorous and covers its body with dust so as to conceal itself from its prey. The adult is active on the wing.
Coriscus subcoleoptratus, Kirby, 1837.
Syn.: Nabicula subcoleoptrata, Kirby, 1837; Nabis subcoleoptratus, Reuter, 1872; Coriscus subcoleoptratus, StÅl, 1873.
Northern United States. Howard was bitten by one between the fingers—the pain was intense, like a needle prick, but the swelling was small.372 No other case known.
Rasahus biguttatus, Say, 1831.
Syn.: Pirates biguttatus, StÅl, 1862; Callisphodrus biguttatus, StÅl, 1866; Rasahus biguttatus, StÅl, 1872.
Common in southern United States, and found in Cuba, Panama and ParÁ, etc. Known as the two-spotted corsair on account of the great spot on the hemielytra. Frequently found in houses, where it chases the bed bug. It also bites man frequently. From 1869 Walsh and Riley placed it amongst the parasites of man. In the United States Davidson373 is of opinion that all cases attributed to spider bites are due to this insect.
Melanolestes morio, Erichson, 1848 (Non-walker).
Syn.: Pirates morio, Erichson, 1848; Melanolestes morio, StÅl, 1866; Pirates picipes, Herrich-SchÄffer, 1848; Melanolestes picipes, Howard, 1900.
Guiana and Mexico and eastern and southern United States. Length 20mm., hides under stones and logs during daylight, and flies at night. Attracted by lights into houses. Very abundant in 1899 at Washington. Howard cites cases where it was proved to bite man.
Melanolestes abdominalis, Herrich-SchÄffer, 1848.
Syn.: Pirates abdominalis, Herrich-SchÄffer; Melanolestes abdominalis, Uhler, 1875.
Allied to the former; some say similar, but can be told by the shorter wings on the female. It occurs in the same localities as M. morio.
Phonergates bicoloripes.
This reduvid attacks man in Africa.
Family. AradidÆ.
Broad and very flat bugs, with antennÆ of four segments and the beak of three; scutellum short, no cuneus to elytra and the tarsi of two segments. They normally live under the bark of trees, etc., and are found in most parts of the world.
Dysodius lunatus, Fabr. (Pito Bug).
A large species which is found in South America, frequenting houses, and bites very severely.
The Ochindundu.
The bug is described by Wellman (Journ. Trop. Med., April 2, 1906, p.97) as not only feeding on ticks, such as Ornithodorus moubata, but as also attacking man. It is called by the Angola Bantus the ochindundu. It is black in colour; the first two pairs of legs are of a bright red hue. It has curious paddle-like structures on the front four legs, which seem to be designed for securely holding the ticks. It infects native kraals for the sake of preying on ticks. The natives also state that it inflicts a bite which far exceeds in painfulness that of the tick. They compare the bite with that of a poisonous snake.
Family. LygÆidÆ.
Scutellum short; antennÆ four-jointed; ocelli present; membranous part of hemielytra with never more than five nervures. Nearly all vegetable feeders. A few are recorded here as biting man.
Lyctocoris campestris, Fabricius.
Syn.: Acanthia campestris, Fabr. (Lyctocoris domesticus).
Rare in habitations, lives on human blood. Found by Blanchard in a bed at an hotel at Liverpool. The bite is undoubtedly worse than that of Cimex; cosmopolitan. In colour it is ferruginous, shining, legs testaceous; hemielytra slightly shorter and narrower than the abdomen; membranous portion transparent, the apex broadly fuscous. Length 3·8 to 4·8mm.
Rhodinus prolixus, StÅl, 1859.
Sometimes attacks man, and the bite is very painful. It is 25mm. long and 8mm. broad, and occurs in Colombia. It is
[A few other unimportant species are also recorded as biting man, such as Harpactor cruentas, in the South of France; Eulyes amoena, from Borneo and Java; Arilus carinatus, Forster, from Brazil. The latter appears to be the same as the Acanthia serratus, Fabricius.—F.V.T.]
Order. Orthoptera.
[The only Orthoptera recorded as doing actual harm to man are certain wingless locusts found in Africa. The cysticercus stage of a small tapeworm found in rats and man has been found in an earwig (Alcock).
[The strange HemimeridÆ found in West Africa, resembling wingless cockroaches, are parasitic on rats (Cricetomys). PhasmidÆ, or stick insects, are said to be able to eject a fluid which may cause blindness if it comes in contact with the eyes.
Locusts Injurious to Man.
[A wingless locust—Enyaliopsis durandi, Luc—is recorded by Wiggins374 as injurious to man in Uganda. “The bite of this insect,” it is said, “gives rise to a very nasty eruption, which may extend over the whole body, with high temperature and general malaise. The skin at the site of the bite sloughs away, and generally leaves a large deep cavity, which heals very slowly.”
[An allied species—E. petersi, Schaum—emits a clear yellow fluid, but according to Marshall this does no harm.375 Stannus writes that “for some years I have been cognizant of the fact that among the natives of Nyasaland an allied if not the same species is held to cause skin lesions by the emission of a fluid on the bare skin surface of the body. I have seen cases of ulcers on various parts of the body, for which the ‘nantundua’ was assigned as the cause.” He then describes the destruction of the superficial layers of the skin which he observed after the yellow fluid had been on the skin twelve hours.—F.V.T.]
Order. Coleoptera.
The larvÆ of beetles, similarly to those of some other Arthropoda (myriapods and the larvÆ of gnats), have sometimes been observed in man as purely accidental guests. In one case or another, such accounts may have originated through a mistake of the observer. Thus English doctors report the presence of the larvÆ of Blaps mortisaga in the stools of human beings, Sandberg of the larva of Agrypnus murinus in his ten year old son, and Blanchard mentions the larva of a beetle that was vomited by a child. All these cases, however, do not represent actual parasitism, although there are beetles living parasitically.376
Silvanus surinamensis, LinnÆus (Saw-toothed Grain Beetle).
[Taschenberg records this beetle as having invaded some sleeping apartments adjoining a brewery where stores were kept, and annoying the sleepers at night by nipping them when in their beds.
[This beetle is common in many parts of the world amongst groceries, corn, meal, seeds, dried fruits, etc. It is about 110in. long, much flattened and chocolate-brown in colour. The thorax has two shallow grooves and bears six minute teeth on each side. The jaws are strong, but the bite cannot be very serious.—F.V.T.]
Order. Diptera or Siphonaptera.
Aphaniptera (Fleas).
Wingless, the thoracic rings distinct and free; antennÆ of three segments; legs very powerful; abdomen with nine segments. [Ten segments are present, but only nine are visible.—F.V.T.] The mandibles transformed into serrated puncturing organs, which are situated in the split sheath of the rostrum; the maxillÆ are laminated and have palpi, and more or less conceal the other parts.
The importance of fleas lies mainly in the fact that they act as plague carriers. About 150 species have already been described. The only ones of importance for this work are those found on man and those on rats and mice. The two families in which these are found are known as PulicidÆ and SarcopsyllidÆ.
The eggs of fleas are laid on the ground, on rugs, etc., and in birds’ and rodents’ nests. They hatch rapidly in warm weather and in warm climates, varying from two to five days; in cold countries they may take two or three weeks to incubate.
The larva is a footless creature, pearly white in colour, the head sometimes being darkened, composed of fourteen segments including the head, and although apodal can move with considerable agility. It lives amongst dust and dirt, and feeds upon any organic matter it can find. In about two weeks it is said to become mature, and then spins a cocoon in which pupation takes place.
The cocoons of the common human flea and the fowl flea become covered with dust and dirt. The period of pupal life seems varied, for I have had the fowl flea hatch out in ten days, and others in three weeks at the same time of year.
The adults are blood suckers and cause considerable irritation as well as acting as disease carriers, and in the SarcopsyllidÆ the females attach themselves permanently to their hosts, embedding themselves under the skin, where they become pregnant. Some kinds harbour the cystic stage of tapeworms, and the rat trypanosome passes certain stages in the rat flea. Most fleas have definite hosts, but some, like the rat and fowl fleas, attack man.
The fleas which can carry the bacillus of plague are Xenopsylla cheopis, Pulex irritans, Ceratophyllus fasciatus and Hoplopsyllus anomalus.
The two families, PulicidÆ and SarcopsyllidÆ, can be distinguished as follows:
| Thoracic segments much foreshortened, coxÆ and femora of hind legs very slightly enlarged | SarcopsyllidÆ. |
| Thoracic segments normal, coxÆ and femora of all the legs much enlarged | PulicidÆ. |
Family. SarcopsyllidÆ (Jiggers).
| The members of this family are not confined to one host. | |
| Three genera are known and tabulate as follows:— | |
| a. Hind coxa without a patch of spines on the inside. | |
| a1. Hind femur simple | 1. Dermatophilus. |
| a2. Hind femur with a large tooth-like projection near the base | 2. Hectopsylla. |
| . Hind coxa with a patch of short spines on the inside | 3. Echidnophaga. |
Genus. Dermatophilus, GuÉrin.
Dermatophilus cÆcata, Enderl.
The eyes of the female vestigial. Taken on and behind the ears of Mus rattus in Brazil.
Dermatophilus penetrans, L., 1758 (Jigger, Chigoe).
Syn.: Sarcopsylla penetrans.
About 1 to 1·2mm. in length; brown in colour. Eyes distinct. The males only occasionally visit man to bite; the fertilized female, on the other hand, bores into the skin with her head, particularly about the toes of the host, and then attains considerable dimensions. The eggs develop on the soil with a metamorphosis similar to that of the common flea.
Fig. 380.—Dermatophilus penetrans: young female. Highly magnified. (After Moniez.)
Fig. 381.—Dermatophilus penetrans: older female. Enlarged. (After Moniez.)
The sand flea (nigua) particularly infests Central and South America, and, in 1873, was carried by ships from Brazil to the West Coast of Africa. In a comparatively short time it has become disseminated throughout Africa and has also appeared in Madagascar; recently also it has been reported from China.
Besides attacking man, it also settles on mammals, for instance, on dogs, pigs, etc. According to Jullien the wound or little swelling caused by the female has no particular significance, as children infested with ten or eleven sand fleas quietly proceeded with their games. It will be understood, however, that the wound easily affords the opportunity for the setting up of inflammation or even septic processes, as is the case in any kind of wound.
[The jigger is also well known in the West Indies.—F.V.T.]
Genus. Echidnophaga, Olliff.
Four species found on rats, etc.
Echidnophaga gallinacea, Westwood (Chigoe of Fowls).
[This flea is a native of tropical Asia and Africa. It lives on the fowl chiefly, attacking the neck and around the eyes. Specimens
[Three other species are found on rats, viz.: E. myrmecobii, Rothsch., from Australia; E. murina, Tirah, from Southern Europe; and E. liopus, Rothsch., India and Western Australia.—F.V.T.]
Family. PulicidÆ (True Fleas).
Rothschild’s classification is as follows:—
| Section I.—Club of antennÆ distinctly segmented only on the hind side. | |
| Key to Genera. | |
| a. No comb on head and thorax. | |
| a1. The internal incrassation, which extends from the insertion of the mid coxa into the thorax, joins the anterior edge of the mesosternite | Pulex. |
| b1. This incrassation joins the upper edge of the mesosternite | Xenopsylla. |
| b. With a comb on the pronotum only | Hoplopsyllus. |
| c. With a comb on the pronotum and at the lower edge of the head | Ctenocephalus. |
| Section II.—Club of antennÆ distinctly segmented all round. | |
| Key to Genera. | |
| a. Eye developed. | |
| a1. No comb on head. | |
| a2. Pygidium not projecting backwards; frons with tubercle | Ceratophyllus. |
| b2. Pygidium strongly convex, projecting backwards; frons without tubercle | Pygiopsylla. |
| b1. Two spines at angle of genÆ | Chiastopsylla. |
| b. Eye vestigial or absent. | |
| a1. Abdomen without comb. | |
| a2. Hind edge of tibiÆ with about eight short and several long bristles, which do not form a comb. | |
| a3. Fifth segment in fore and mid tarsi with five, and in hind tarsus with four bristles | Neopsylla. |
| b3. Fifth segment in fore and mid tarsi with four, and in hind tarsus with three lateral bristles, there being an additional pair of bristles in all the tarsi on the ventral surface in between the first pair | Ctenophthalmus. |
| b2. Hind edge of tibiÆ with about twelve short and three long bristles, the short ones forming a kind of comb | Ctenopsylla. |
| b1. Abdomen with at least one comb | Hystricopsylla. |
Genus. Pulex, Linn.
Pulex irritans, L., 1758.
Male 2 to 2·5mm. in length, females about 4mm.; reddish or dark brown; head without bristles; thoracic and abdominal rings of bristles on the dorsal aspect, and small hairs directed backwards at the posterior margin. The barrel-shaped white eggs are deposited
Fig. 382.—Pulex irritans. 14/1.
Fig. 383.—Larva of flea. Enlarged. (After Railliet.)
Fig. 384.—Pulex serraticeps. 22/1.
Fleas live in human dwellings all over the world, and periodically pass on to persons to suck their blood. They may deposit their eggs on very uncleanly individuals, and even undergo development, therefore it is possible to find larvÆ and pupÆ on such persons.
The dog flea, Pulex serraticeps, is easily distinguished from the flea of man by the large thick bristles on the posterior margin of the first thoracic ring (fig.384).
Genus. Xenopsylla, Glink.
Xenopsylla cheopis, Rothschild.
This is the common rat flea of tropical countries. Rothschild377 says: “Although practically cosmopolitan, it cannot apparently flourish in temperate and cold climates.”
In the male the bristles of the flap-like process of the clasper all slender; in the female the narrow portion of the receptaculum seminis long. Originally discovered in Egypt.
This is apparently the chief plague flea. The Indian Plague Committee have proved that this flea is easily infected when fed on plague rats, and that the bacillus multiplies rapidly in the flea’s stomach and that the fleas may remain infective for fifteen days. How the flea infects man does not apparently seem to have been proved, as it does not do so through its bite, but the excrement is highly infective. It is probable that this poisoned fÆcal matter gets to the wound caused by the piercing mouth.
Xenopsylla brasiliensis, Baker,
occurs on rats in West Africa and has been introduced into Brazil.
Genus. Ctenocephalus, Kolen.
Includes the cat and dog fleas. The dog flea, C. canis, DugÈs, is found on the dog all over the world, but especially in temperate climates. It also occurs on rats. Man is often badly bitten by this insect and it overruns houses. The eggs are laid on rugs, carpets and dust and dirt and amongst dogs’ hair, but are not fastened to it and fall anywhere. The ova may hatch in about fifty hours and the larvÆ live for seven days and then spin their cocoons amongst dust and dirt. The pupal stage lasts about eight days.
The cat flea (C. felis) is widely distributed over the world, and occurs on many mammals beyond the cat, and is also found on rats.
Genus. Hoplopsyllus, Baker.
A genus found in North America related to Pulex, but at once recognized by the prothorax bearing a comb.
Hoplopsyllus anomalus, Baker,
which is found on the ground squirrel (Citellus beecheyi) in California, and according to Rothschild once found on the rat, has been proved to carry the plague bacillus and to play an important part in plague infection in California.378
Genus. Ceratophyllus, Centis.
Ceratophyllus fasciatus, Bosc.
This flea is also found on the rat in Europe and will attack man. It is a plague carrier. It has eighteen to twenty teeth on the
Genus. Ctenopsylla, Kolen.
This genus contains a very abundant rat and mouse species, C. musculi, DugÈs, which is widely distributed over the globe.
Genus. Hystrichopsylla, Tasch.
Large hairy fleas, with no eyes and one or more combs on the abdomen. In the Mediterranean area one species, H. tripectinata, Tirah, is common on rats and mice, and also in the Azores. Several others occur on rats and mice. For information concerning these the reader is referred to Rothschild’s papers.
Pulex pallipes is another species found on the rat and man.
Systematic, Anatomical, and Biological Remarks on Mosquitoes.
Mosquitoes come in the Nematocera, one of the sub-orders of the Diptera, and are divided into numerous families, of which, however, the CulicidÆ are of most interest to us here. Other families as the PsychodidÆ and ChironomidÆ are also of considerable importance, vide following pages. The head is small, the facetted eyes are placed laterally, but there are no accessory eyes (ocelli). In front of the eyes are situated the comparatively long antennÆ, the differences of which strongly mark the distinction of sex.379
The antennÆ are composed of fifteen or sixteen segments. In the male they are covered with long whorl-like hairs, while in the female the antennal hairs are short—differences that are perceptible even with the naked eye.380 The proboscis, which is longer than the antennÆ, protrudes from the inferior aspect of the head and is composed of the following parts (figs.387 and 388): Two grooved half tubes, facing one another, of which the upper one is the upper lip (labrum) and the lower one the lower lip (labium), which represents a pair of coalesced maxillÆ. Within the tube formed by the labrum and labium are the mandibles and maxillÆ, transformed into instruments for piercing, and a single puncturing organ, the hypopharynx. On the right and left, next to the proboscis, are placed the straight five-jointed palpi, the final joint of which is thickened in the male.381 In biting, the labrum, which is swollen at its free end, is not introduced into the wound like the
The three thoracic segments are soldered together. The central one carries the membranous wings on the sides of the dorsal surface; the posterior somite carries the small halteres (rudimentary posterior wings). There are three pairs of long slender legs on the lower side.
Fig. 385.—Head of a male (a) and of a female (b) Anopheles. Slightly enlarged. (After Giles.)
Fig. 386.—Head of a male (a) and of a female (b) Culex. (After Giles.)
Fig. 387.—Mouth parts of Anopheles claviger.† h., hypopharynx; md., mandible; mx., maxilla; u.l., upper lip; l.l., lower lip; p., palpi. (After Grassi.)
† [This should read Anopheles maculipennis, Meig.; there was no type of A. claviger.—F.V.T.]
Fig. 388.—Anopheles maculipennis: transverse section through the proboscis of a female (a) and a male (b). hy., hypopharynx, with duct of the salivary gland; m., muscles; md., mandibles; mx., maxillÆ; l., labium; l.l., labrum. (After Nuttall and Shipley.)
The abdomen has no limbs, is composed of eight (rarely nine) distinct segments; the sexual and anal orifices are at the posterior end, the stigmata on the sides. The intestinal canal (fig.389) is composed of three principal divisions; the anterior part reaches as far as the front pair of legs, and consists of the oesophagus, which is provided with two small lateral diverticula. [At the commencement of the oesophagus are one or more diverticula, which vary in size; they contain air, food
The pair of salivary glands have one common excretory duct leading into the hypopharynx.
Fig. 389.—Longitudinal section of an Anopheles, showing alimentary canal. In the forepart of the thorax is the salivary gland consisting of three tubules; ventrally, the suctorial stomach extending into the abdominal cavity; the stomach, and at the posterior end of the abdomen the Malpighian vessels. (After Grassi.)
These glandular bodies are situated in the thorax; each consists of three slightly serpentine tubules, the dorsal and ventral tubes being long, the central one shorter. The above-named characteristics apply to both genera Culex and Anopheles, but in the genus Culex is smaller, Anopheles larger. [In Anopheles the ends of the ducts in the lobules are dilated, whilst in most of the genera the ducts are the same size all along. The lobules may bifurcate, and in Psorophora there are five lobules.—F.V.T.] The legs of the genus Culex are about the same length as the whole body; in Anopheles they are double that length.382 In Anopheles the palpi and proboscis are of equal length; in Culex the condition is different, according to sex. In the male the palpi are longer than the proboscis; in the female considerably shorter and the number of segments diminished. The venation of the wings exhibits further points of differentiation, as also their adornment, though this last sign is not by any means always conclusive; most species of the genus Culex have unspotted wings, whilst those of Anopheles are usually spotted. More important is the fact that in Culex the abdomen is decorated with small scales, similar to those on butterflies, whereas there are small bristles on the abdomen of Anopheles. [This cannot be said to be a character by which an Anopheline may be told from a Culicine, for in such common Anopheline genera as Cellia and Neocellia we get plenty of scales on the abdomen.—F.V.T.] An experienced observer can, however, separate the two genera by the difference in size and their manner of resting. When settled they either touch the resting place with all the legs or only with the four anterior legs. In consequence of the different length of the legs, the body of Culex approaches the resting place more closely; moreover, Culex holds the abdomen parallel or at an acute angle to the resting surface, whereas Anopheles carries the abdomen directed upwards (at an angle of about 145°) and holds the head down. Both genera, however, usually only rest on the four anterior legs, and then, as has long been known, Culex carries the third pair directed towards the dorsum, while those of Anopheles hang down.
In regard to the differentiation of the species, I must refer you to the special literature, and content myself by observing that about 150 species of Culex and about fifty species of Anopheles have been described, of which fifty about four are
Fig. 390.—Anopheles maculipennis, Meigen. Enlarged. (After Grassi.)
Everyone is aware that mosquitoes swarm at sunset in fine weather, and then seek out human beings and other warm-blooded animals to take food. In this regard, however, the sexes differ, for it is almost without exception that the females only suck blood, while the males subsist on the juices of plants (blossoms or fruits).
[Some mosquitoes bite in the daytime—Stegoymia and some Anophelines; some bite right into the night, as Culex fatigans and C. pipiens.—F.V.T.]
The period required for digestion varies according to the temperature. It takes two days in summer, and may take up to ten days or more in cool weather. After digestion is complete more food is taken up, this being necessary [in some species only—F.V.T.] for the maturing of the sexual products in the female.
Fig. 391.—Larva of Anopheles maculipennis, Fabr. Enlarged. (After Grassi.)
Fig. 392.—Larva of Culex. Enlarged. (After Grassi.)
It is still unknown under what circumstances copulation takes place;385 in any case, sooner or later the females are fecundated, and when the ova have become mature, and the season is not too far advanced, they seek a suitable place in which to deposit them.386 These are larger or smaller, permanent or temporary, collections of standing water, pools, puddles, lakes, pits, water in rain-water barrels, basins, etc. Nevertheless, certain kinds prefer certain waters; thus Anopheles (claviger) maculipennis and several of the Culices seek stagnant water overgrown with swamp vegetation and decomposing vegetable matter; A. bifurcatus and certain Culices, clear water with some vegetation (such as fountains and the lakes in gardens and parks); Culex pipiens has a preference for rain-water barrels, even though the water be dirty and evil-smelling. [I have found the larvÆ of Anopheles bifurcatus living in great numbers in ponds and lakes completely overgrown with floating water-weeds, and those of Culex pipiens in liquid manure.
Sexual Organs of the Mosquito.—The female has a pair of ovaries, opening into a single tube by the ovarian tubes; into the single tube opens a duct coming from the spermathecÆ, and also a mucous gland. The spermathecÆ store up the male cells. The male organs consist of two testes joined by ducts (vasa deferentia) to the ejaculatory duct formed by their union. Each vas deferens is joined by a short tube with the sac-like vesicula seminalis.—F.V.T.]
There is also a difference in the manner in which Culex and Anopheles deposit their ova. Culex deposits two to three hundred eggs in compact heaps that float on the water, and in which the eggs stand perpendicularly one next the other; whereas Anopheles maculipennis deposits only three or four up to twenty eggs, united in groups that float horizontally on the water; the eggs of A. bifurcatus, again, are arranged in star-like groups. The eggs are about 0·75mm. in length, and assume a dark hue soon after being laid. The development only occupies a few days. The young larvÆ grow rapidly, changing their integument several times; the larvÆ also differ in the various genera, though they have a general resemblance (figs.391 and 392).
The long legless larva has a flattened head, a fairly broad, rectangular, or trapeziform thorax, on which there are bristles, and an abdomen distinctly segmented, and on the segments of which there are also lateral bristles. The situation of the stigmata marks the difference between the two genera. Though in both genera the stigmata are at the posterior end and on the dorsal surface, they are in Anopheles close to the surface of the body; in Culex, however, they are on the free end of a long tube (siphon).
Fig. 393.—Pupa of Anopheles maculipennis, Meig. Enlarged. (After Grassi.)
The position of the larva in the water also differs. The larva of Anopheles lies almost horizontally beneath the surface of the water, the posterior border of the penultimate abdominal segment, upon which the stigmata are situated, being on the surface; whereas the larva of Culex hangs head downwards perpendicularly in the water, the point of the siphon only touching the surface.
In about a fortnight the larva is fully grown and becomes a pupa. The pupa
The females that are fertilized in the autumn hibernate in sheltered spots in the open air, or in houses, cellars, under stairs, in stables, barns, etc., and are the progenitors of the first generation of the following year.
In accordance with the climate of a country, or the kind of weather of a year, the conditions in regard to the manner of life and the duration of the development of the mosquito vary. At all events, the life-history of the mosquito elucidates many points relating to malaria which were hitherto not understood.
[The length of the egg, larval and pupal life varies so much that it is not possible to give an account of any value here. Frequently the eggs may incubate in two days, whilst I have had Stegomyia fasciata eggs from Cuba that have hatched out under abnormal circumstances more than two months after they were laid (“Mono. Culicid.,” iii, p.6). Some larvÆ, as Anopheles bifurcatus, live for months during the winter. Some mosquitoes therefore hibernate as larvÆ. The larvÆ and pupÆ of the different genera present very marked characters, mainly in regard to the structure of the siphons. Specific differences may be found in the frontal hairs of Anopheline larvÆ and in the number and arrangement of a group of spines at the base of the siphon in Culicines.—F.V.T.]
CulicidÆ or Mosquitoes.
The importance of these insects to man is very great. They not only produce painful bites, which may become inflamed and give rise to a considerable amount of oedema, but they are more important on account of the part they play in the distribution of various diseases. CulicidÆ may not only carry disease germs, but act as intermediate hosts for certain parasites, such as some of the Anophelina for malarial parasites, Culex for FilariÆ, and Stegomyia for yellow fever, etc.; the last-named is in any case the distributor of that fatal disease. It is therefore very necessary to know the life-history, habits and characters of these pests.
Mosquitoes exist in almost all parts of the world from the Arctic circle to the tropics; temperate regions suffer from them less than the two extremes, but even there they form not only a source of great annoyance but of danger as malaria and possibly now and again yellow fever carriers. A few years ago comparatively few species were known, now some 800 odd have been described. Their number will probably not stop far short of 1,000, in spite of the fact that many have been described under different names, yet really the same species. Some are purely domestic, others entirely sylvan; the former, as we might expect, often have a very wide distribution, having been taken from place to place in boats and trains. The more rapid transport becomes, the greater becomes the possibility of this wide distribution of many species increasing, and the spread of other species from their natural home to foreign parts by sea and then by trains further inland.
Fig. 394.—Heads of Culex and Anopheles: (1) Culex male; (2) Culex female; (3) Anopheles male; (4) Anopheles female. (After Daniels.)
All CulicidÆ are aquatic in their larval and pupal stages. Almost all small collections of water, both natural and artificial, may form breeding grounds for these pests. Some even breed in pitcher plants and many in bromelias. The
Fig. 395.—a, eggs of Culex; b1 b2, eggs of Anopheles; c, egg of Stegomyia; d, egg of TÆniorhynchus; e, egg of Psorophora.
There are two main types of larvÆ, the Anopheline and Culicine; in the former there is no respiratory siphon, in the latter the siphon is long or moderately long. The head offers certain marked peculiarities which are of specific value; this especially applies to the Anophelina, in which the frontal hairs are of great service in distinguishing the larvÆ,388 whilst in Culex the number and position of the spines at the base of and on the siphon are characteristic. The position assumed by the larvÆ in the water also varies in the different groups; most of the Anophelines lie horizontally, most of the Culicina and Ædeomyina hang head downwards. The
Fig. 396.—Diagram showing the structure of a typical mosquito. (Theobald.)
The eggs, which may be laid separately (Anopheles maculipennis, Stegomyia fasciata, Joblotia nivipes, etc.), or in rafts (Culex pipiens, C. fatigans) or in chains (PseudotÆniorhynchus fasciolatus), present a great variety of forms. The most peculiar are shown in fig.395 (TÆniorhynchus, Culex, Stegomyia, Anopheles, Psorophora).
As in all insects, they differ very materially in each species of one genus. Those best known are the Anopheline eggs.
The eggs always float on the surface of the water; immersion soon destroys them, but many may occur in mud and can resist desiccation.
Fig. 397.—Types of scales, a to k; head and scutellar ornamentation, 1 to 5; forms of clypeus, 6. (Theobald.) 1, head and scutellum of Stegomyia, etc.; 2, of Culex and Mansonia; 3, of Howardina, Ædes, etc.; 4, of Megarhinus and Toxorhynchites, etc.; 5, of Cellia and some other Anophelines; 6, a', clypeus of Culex; b' of Stegomyia; c', of Joblotia.
Characters of Adult CulicidÆ.—The chief characters by which true mosquitoes, or CulicidÆ, are known are the following:—
(1) Wings always with the veins covered with scales; the longitudinal veins,
(2) Head, thorax and abdomen usually, but not always (Anopheles, etc.), covered with scales.
(3) Mouth parts formed into a long piercing proboscis.
As a rule the males may be told from the females by their antennÆ being plumose, whilst in the females they are pilose (vide fig.394), but this does not invariably hold good, for in Deinocerites, Theobald, and Sabethes, Desvoidy, and others, they are pilose in both sexes. The labial palpi are very variable in regard to their form and the number of segments; in the Anophelina they are long in both sexes, as long or nearly so as the proboscis, more or less clubbed in the males; in Culicina, Joblotina and Heptaphlebomyia, they are long in the males, short in the females; in Ædeomyina, short in both sexes.
Fig. 398.—Neuration of Wing. Explanation of Wing, Veins and Cells.—A, costal cell; B, sub-costal cell; C, marginal cell; D, first sub-marginal cell (= first fork cell); E, second sub-marginal cell; F, first posterior cell; G, second posterior cell (= second fork cell); H, first basal cell; I, second basal cell; J, third posterior cell; K, anal cell; L, auxiliary cell; M, spurious cell; c, costal vein; 1st—6th, first to sixth longitudinal veins; a, a' and a'', incrassations (a' called by Austen the sixth vein, a'' the eighth vein); y, supernumerary cross vein; z, mid cross vein; p, posterior cross vein; s.c., sub-costal. (Theobald.)
Scales.—The most important structural peculiarities in CulicidÆ are the scales, which form the chief and most readily observed characters for separating genera and species. The importance of scale structure has been recently ignored by some workers, who are probably right academically, but as a means of separating groups, and so more easily running down a species, the practical man is strongly advised to follow this method. As to what a genus is, is purely a matter of personal opinion. If one examines any recent standard work on entomology one will find a species being placed in varied genera by the varied authorities.
The head, thorax, abdomen and wings are in nearly all cases clothed with squamÆ of varied form, of which the following are the main types (fig.397):—
(1) Flat, spade-shaped scales (a).
(2) Narrow curved scales (e).
(3) Hair-like curved scales (d).
(4) Spindle-shaped scales (f).
(5) Small spindle-shaped scales (g).
(6) Upright forked scales (h) and (i).
(7) Twisted upright scales (j).
(8) Inflated or pyriform scales (k).
(9) Mansonia scales (b).
(10) Small broad asymmetrical scales (c).
Various other varieties are found on the wings, such as:—
(1) Narrow linear lateral scales.
(2) Narrow lanceolate scales.
(3) Broad lanceolate scales.
(4) Elongated, broad, truncated scales (= PseudotÆniorhynchus-like scales).
(5) Pyriform scales.
(6) Asymmetrical broad or TÆniorhynchus scales.
(7) Flat spade-like scales.389
The wings have a series of scales along the middle line of the veins, and also lateral scales to all or nearly all the veins. The wing is also fringed by a series of scales (fig.396), which, however, are of little systematic importance; the so-called “border scales” (b.s.) vary, however, to some extent, and are useful characters in separating some of the TÆniorhynchus.
The Classification of CulicidÆ.
| I. | Wings with six-scaled longitudinal veins. | |||||
| A. | Palpi long in the male. | |||||
| a. | Palpi long in both sexes, clavate in ? Anophelina. | |||||
| I. | First submarginal cell as long or longer than the second posterior cell. | |||||
| Antennal segments without dense lateral scale tufts. | ||||||
| Thorax and abdomen with hair-like scales | Prothoracic lobes simple; no flat head scales | Wing scales lanceolate | Anopheles, Meigen. | |||
| Wing scales mostly long and narrow | Myzomyia, Blanchard. | |||||
| Wing scales as above, but fourth long vein near base of third and outstanding scales on prothoracic lobe | Neomyzomyia, Theobald. | |||||
| Wing scales partly large and inflated | Cycloleppteron, Theobald. | |||||
| Prothoracic lobes mammillated; some flat head scales. Basal lobe of ? genitalia of two segments | Stethomyia, Theobald. | |||||
| Prothoracic lobes with dense outstanding scales | Feltinella, Theobald. | |||||
| Thorax with some narrow curved scales; abdomen hairy | Pyretophorus, Blanchard. | |||||
| Wing scales small and lanceolate. Wing scales broad and lanceolate | Myzorhynchella, Theobald. | |||||
| Thorax with hair-like curved scales, some narrow curved ones in front; abdomen with apical lateral scale tufts, scaly venter; no ventral tuft | Arribalzagia, Theobald. | |||||
| Thorax with hair-like curved scales; abdominal scales on venter only, with a distinct ventral apical tuft | Myzorhynchus, Blanchard. | |||||
| Much as above, but abdomen with long spine-like dense lateral tufts | Chrystia, Theobald. | |||||
| Thorax with very long hair-like curved scales; abdomen pilose, except last two segments which are scaly; dense scale tufts on third femora; wings with broadish, blunt, lanceolate scales | Lophoscelomyia, Theobald. | |||||
| Thorax and abdomen with scales | Abdominal scales as lateral dorsal patches of small flat scales; thoracic scales narrow and curved, or spindle-shaped | Nyssorhynchus, Blanchard. | ||||
| Abdomen nearly completely covered with irregular scales and with lateral tufts | Cellia, Theobald. | |||||
| No lateral scale tufts | Neocellia, Theobald. | |||||
| Thoracic scales hair-like except a few narrow curved ones in front; abdominal scales long, broad and irregular | Kerteszia, Theobald. | |||||
| Thorax with hair-like curved scales and some broad straight scales, others spatulate on sides. Abdomen covered with fine hairs except last three segments, which are scaly. Tufts of scales on hind femora. Wing scales lanceolate | Manguinhosia, Cruz. | |||||
| Antennal segments with many dense scaly tufts | Chagasia, Cruz. | |||||
| AntennÆ with outstanding scales on second segment, more appressed ones on the first. At least one segment of abdomen with long flat more or less spatulate scales | Calvertina, Ludlow. | |||||
| II. | First submarginal cell very small | Bironella, Theobald. | ||||
| With a distinct cylindrical tubercle projecting obliquely from the prothoracic region | Dactylomyia, Newstead and Carter.390 | |||||
| Scutellum trilobed. | ||||||
| First submarginal cell much smaller than the second posterior cell; proboscis long and bent | MegarhininÆ. | |||||
| Palpi long in both sexes | Megarhinus, Rob. Desvoidy. | |||||
| Last segment of ? palpi blunt. Last segment of ? palpi long and pointed | Ankylorhynchus, Lutz. | |||||
| . | Palpi short in the female | Toxorhynchites, Theobald. | ||||
| First submarginal cell longer than the second posterior cell | CulicinÆ. | |||||
| Legs more or less densely scaly; head not entirely clothed with flat scales; all the legs densely scaly. | ||||||
| Wings with large pyriform scales | Mucidus, Theobald. | |||||
| Wings with narrow scales | Psorophora, Rob. Desvoidy. | |||||
| Hind legs only densely scaled | Janthinosoma, Arribalzaga. | |||||
| Head entirely clothed with flat scales. Legs uniformly scaled with flat scales. Head and scutellar scales all flat and broad. Palpi of ? short, of ? thickened apically and tufted | Stegomyia, Theobald. | |||||
| Palpi of ? longer than in Stegomyia and in ? long and thin, acuminate, simple | Desvoidea, Blanchard. | |||||
| Head scales mostly flat, but a median line of narrow curved ones; scutellar scales flat on mid lobe, narrow curved on lateral lobes and palpi longer than proboscis | Macleayia, Theobald. | |||||
| Head scales mostly flat, irregular, narrow curved ones behind; mid lobe scutellum with flat scales, lateral with narrow curved; ? palpi shorter than proboscis | Catageiomyia, Theobald. | |||||
| Head scales mostly flat, but a few narrow curved ones in middle in front; scutellar scales all flat | Scutomyia, Theobald. | |||||
| Head scales all flat; scutellar scales all narrow curved | Skusea, Theobald. | |||||
| Head with flat scales, except a small median area of narrow curved ones; scutellar scales all narrow curved | Howardina, Theobald. | |||||
| Head with all flat scales except a thin line of narrow curved ones behind; scutellar scales all narrow curved | Danielsia, Theobald. | |||||
| Head with small flat scales over most of surface, with median line and line around eyes of narrow curved ones; scutellar scales bluntly spindle or club-shaped | Hulecoetomyia, Theobald. | |||||
| Head and scutellar scales narrow curved. Wing scales long, narrowly lanceolate, collected in spots; palpi clubbed in ?; five-jointed and rather long in ? | Theobaldia, Neveu-Lemaire. | |||||
| Wing scales (lateral) long and narrow, and ? palpi three-jointed, ? not clubbed and hairy | Culex, LinnÆus. | |||||
| Wing scales at apex of veins dense and rather broad, femora swollen; small dark species | Melanoconion, Theobald. | |||||
| Wings with short, thick, median scales and short, broadish lateral ones on some of the veins; scales mottled; fork-cells rather short | Grabhamia, Theobald. | |||||
| Wings with dense, broadish, elongated, truncated scales | PseudotÆniorhynchus, Theobald. | |||||
| Wings with broad, short, asymmetrical scales | TÆniorhynchus, Arribalzaga. | |||||
| Head covered with rather broad, flat, spindle-shaped scales; scutellum with small flat scales to mid lobe | Gilesia, Theobald. | |||||
| Head clothed with flat, irregularly disposed scales all over, with patches of narrow curved ones; ? palpi clubbed | Acartomyia, Theobald. | |||||
| Abdomen with projecting flat lateral scales with deeply dentate apices; wings not ornamented | Lasioconops, Theobald. | |||||
| Wings ornamented; scutellum with flat and narrow curved scales | Finlaya, Theobald. | |||||
| ?. | Palpi short in ? and ? | Ædeomyina. | ||||
| Wings unornamented. | ||||||
| AntennÆ pilose in ? and ?; second joint very long | Deinocerites, Theobald. | |||||
| AntennÆ plumose in the ?. | ||||||
| Head clothed with narrow curved and flat scales. | ||||||
| Mid-lobe of scutellum with six border-bristles. | ||||||
| Scutellum with narrow curved scales. | ||||||
| Palpi in ? four-jointed, in ? two-jointed | Ædes, Meigen. | |||||
| Mid-lobe of scutellum with four border bristles. | ||||||
| Scutellum with flat scales. | ||||||
| Head clothed with flat scales only. | ||||||
| Fork-cells normal length. | ||||||
| Mid-lobe of scutellum with four border-bristles. | ||||||
| Palpi of ? two-jointed | Verallina, Theobald. | |||||
| Palpi of ? five-jointed, metallic | HÆmagogus, Williston. | |||||
| Fork cells very small or small. | ||||||
| Scutellar scales flat. | ||||||
| First submarginal cell longer than the second posterior cell; no flat scales on mesothorax | Ficalbia, Theobald. | |||||
| First submarginal cell smaller than the second posterior cell; flat scales on mesothorax | UranotÆnia, Arribalzaga. | |||||
| Scutellar scales narrow curved. | ||||||
| First submarginal cell as in UranotÆnia | Mimomyia, Theobald. | |||||
| Wings ornamented with Mansonia-like scales | Ædeomyia, Theobald. | |||||
| a. | With chÆtÆ only. | |||||
| Proboscis longer than whole body; lateral wing scales TÆniorhynchus-like | Phoniomyia, Theobald. | |||||
| Proboscis as long as whole body in ? frons drawn out into a prominence; wing scales rather broad and long | Binotia, Blanchard = Runchiomyia, Theobald. | |||||
| Proboscis not as long as the whole body; lateral vein scales narrow | Wyeomyia, Theobald. | |||||
| Proboscis not as long as whole body, swollen apically; wing scales long and broad | Dendriomyia, Theobald. | |||||
| . | Metanotum with squamÆ and chÆtÆ. | |||||
| Palpi short in ? and ?. | ||||||
| Proboscis straight in ? and ?; legs with scaly paddles | Sabethes, Rob. Desvoidy. | |||||
| Venation like Sabethes. | ||||||
| Legs simple | Sabethoides, Theobald. | |||||
| Venation like Culex | Goeldia, Theobald. | |||||
| Proboscis in ? elbowed, with two scaly tufts | Limatus, Theobald. | |||||
| Palpi long in ?, short in ? | Joblotina, Blanchard. | |||||
| II. | Wings with seven-scaled longitudinal veins: Culex type | Heptaphlebomyia, Theobald. | ||||
| piercing | Corethrina. | |||||
| Metatarsus longer than first tarsal joint | Corethra, LinnÆus. | |||||
| Metatarsus shorter than first tarsal joint | Mochlonyx, Ruthe.391 | |||||
Notes on the Different Genera.
Sub-family. Anophelina.
The following Anophelines have been recorded as malaria carriers:—
*Anopheles maculipennis, Meigen.
Anopheles bifurcatus, LinnÆus.
*Myzomyia funesta, Giles.
Myzomyia lutzii, Theobald.
*Myzomyia rossii, Giles.
Myzomyia listonii, Liston.
Myzomyia culicifacies, Giles.
Pyretophorus superpictus, Grassi.
*Pyretophorus costalis, Loew.
Pyretophorus chaudoyei, Theobald.
*Cellia argyrotarsis, Robineau Desvoidy.
Myzorhynchus pseudopictus, Grassi.
Myzorhynchus barbirostris, Van der Wulp.
Myzorhynchus sinensis, Wiedemann.
Myzorhynchus paludis, Theobald.
Myzorhynchus mauritianus, GrandprÉ.
Neocellia stephensii, Liston.
Neocellia willmori, James.
Nyssorhynchus theobaldii, Giles.
Nyssorhynchus fuliginosus, Giles.
Nyssorhynchus annulipes, Walker.
Those marked with an asterisk (*) also carry the larvÆ of Filaria bancrofti, as also do Myzorhynchus minutus, Theobald, and Myzorhynchus nigerrimus, Giles.
Genus. Anopheles, Meigen.
“Syst. Beschr. Europ. zwei. Ins. I,” 1818, ii, p.2, Meigen; “Mono. Culicid.,” 1903, i, p.191; iii, p.17; and 1910, v, p.3, Theobald.
Fig. 399.—Wing of Anopheles maculipennis, Meigen.
This genus contains a few large species found either in temperate climates or in hills and mountains of warm climates. The type is the European and North American A. maculipennis.
A. maculipennis, Meigen. This species and A. bifurcatus are malaria carriers. True Anopheles only occur in Europe, North America, the North of Africa and in the mountains of India, and one has been found by Bancroft similar to A. bifurcatus in Queensland. They are easily told by the absence of scales on thorax and abdomen, and by the rather densely scaled wings with lanceolate scales.
Genus. Myzomyia, Blanchard; Grassia, Theobald.
Comp. rend. heb. Soc. Biol., No. 23, p.795, Blanchard; “Mono. Culicid.,” 1910, iii, p.24; v, p.16, Theobald.
This genus occurs in Asia, Africa and South America, Europe and East Indies. The type is M. funesta, Giles, found in Central and West Africa. Although structurally there is not much difference between this genus and Anopheles, they differ greatly in appearance, and there are usually a few narrow curved thoracic scales projecting over the head, whilst the wing scales are much smaller in proportion, and the wings more uniformly spotted, always so along the costa. Funesta and lutzii are undoubtedly malaria bearers and also rossii.
Genus. Neomyzomyia, Theobald.
“Mono. Culicid.,” 1910, v, p.29.
A single species only occurs in this genus, N. elegans, James, from India. In this genus, which is near to Myzomyia, the fourth long vein is very near the base of the third, and there are outstanding scales on the prothoracic lobes, and there is a marked tuft of dense scales at the posterior angles of the head.
Genus. Cycloleppteron, Theobald.
“Mono. Culicid.,” 1903, ii, p.312; 1903, iii, p.58; 1910, v, p.33.
Two common species only occur in this genus, C. grabhamii, Theob., from Jamaica, and C. mediopunctatus, Theob. (Lutz., ms.), from South America. The chief character is the presence of large black inflated pyriform scales on the wings. The palpi are densely scaled. Neither have been shown to be malaria bearers.
Genus. Feltinella, Theobald.
“Mono. Culicid.,” 1907, iv, p.56.
A single species, so far only found in this genus. The basal lobes of the male genitalia of two segments, the prothoracic lobes with dense outstanding scales.
The species, F. pallidopalpi, Theob., occurs in Sierra Leone.
Genus. Stethomyia, Theobald.
“Mono. Culicid.,” 1903, iii, p.13; 1907, iv, p.59; 1910, v, p.35.
Four species occur in this marked genus—one S. nimba, Theob., from British Guiana and Para, another S. fragalis, Theob., from the Malay States, S. culiciformis, James and Liston, from India, and S. pallida, Ludlow, from India.
The former may be a malaria carrier, for Dr. Low says: “Malarial fever is got amongst the Indians and often of a severe type. In that connection it is interesting that in the interior, at a place called Corato, I got an entirely new Anopheles in large numbers.” The genus is easily told by its unornamented wings, flat head scales, mammillated prothoracic lobes and long thin legs.
Genus. Pyretophorus, Blanchard; Howardia, Theobald.
Compt. rend. heb. Soc. Biol., No. 23, p.705, Blanchard; Journ. Trop. Med., v, p.181; and “Mono. Culicid.,” 1903, iii, p.13; 1910, v, p.36, Theobald.
Forty-four species come in this genus, of which Anopheles costalis, Loew, is the type.
This genus is found in Africa, India, Europe and in Australia. Three species are proved malaria bearers, namely, P. costalis, Loew, P. chaudoyei, Theob., and P. superpictus, Grassi. Members of this genus can be told by having narrow curved thoracic scales, hairy abdomen, and much-spotted wings.
Genus. Myzorhynchella, Theobald.
“Mono. Culicid.,” 1907, iv, p.78.
In this genus the thorax has distinct, narrow curved scales, and the abdomen is hairy, the wing scales broad and lanceolate, and the head with broad scales not closely appressed, but not forked or fimbriated.
Five species are known: lutzi, Cruz; parva, Chagas; nigritarsis, Chagas; tibiomaculata, Neiva; gilesi, Neiva; and nigra, Theobald. They are all recorded from Brazil, and nigra also from Mexico.
Genus. Manguinhosia, Cruz, in Peryassu.
“Os Culicideos do Brazil,” 1908, p.112.
A single marked species from the Brazils. The thorax has piliform curved scales, and some narrow curved and flattened ones on the sides. Abdomen pilose, except the last three segments which are scaled. No tufts of scales on posterior femora.
Allied to Lophoscelomyia, but at once told by the absence of scale tufts on the hind femora. M. lutzi, Cruz, Brazil.
Genus. Chrystya, Theobald.
“Rep. Sleeping Sickness, Roy. Soc. Eng.,” 1903, vii, p.34.
A very marked genus in which the hairy abdomen has very long, dense, hair-like, apical, scaly tufts to the segments. A single species only so far known, C. implexa, Theobald, from Africa (Uganda, Sudan, etc.).
Genus. Lophoscelomyia, Theobald.
Entomologist, 1904, xxxvi, p.12.
A single species only, from the Federated Malay States. The hind femora have dense, apical scale tufts; the thorax long, hair-like curved scales; abdomen pilose, except the last two segments which are scaly; wings with broad, blunt, lanceolate scales.
Genus. Arribalzagia, Theobald.
“Mono. Culicid.,” 1903, iii, pp.13 and 81; and 1910, v, p.48.
Two species only occur, found in South America. The thorax and abdomen have scales and hairs respectively, as in Pyretophorus, but the abdomen has in addition prominent lateral apical scale tufts to the segments and a scaly venter. Wings with membrane tinged in patches and wing scales bluntly lanceolate and very dense. The type is A. maculipes, Theob. found in Trinidad and Brazil; A. pseudomaculipes, Cruz, also in Brazil.
Genus. Myzorhynchus, Blanchard; Rossia, Theobald.
Compt. rend. heb. Soc. Biol., 1902, No. 23, p.795, Blanchard; Journ. Trop. Med., 1902, p.181, Theobald; “Mono. Culicid.,” 1903, iii, p.84; 1907, iv, p.80; 1910, v, p.49.
A very marked genus of large, dark, densely scaled species, found in Europe, Asia, Africa and Australia. The thorax with hair-like curved scales; the abdomen
Fourteen species are known. Five are malaria carriers (vide list, p.566).
Genus. Nyssorhynchus, Blanchard; Laverania, Theobald.
“Mono. Culicid.,” 1910, iii, p.14; v, p.55, Theobald; Compt. rend. heb. Soc. Biol., No. 23, p.795, Blanchard.
A group of small, closely allied species found in Asia, Africa and Australia, twelve out of the twenty species coming from India.
The thorax is covered with narrow curved and spindle-shaped scales, abdomen with small, flat or narrow curved dorsal scales, especially on the apical segments or in patches; the legs are always banded or spotted with white, and the tarsi have as a rule one or more pure white segments. (This banding and spotting is of no generic value, however.)
The species show considerable seasonal variation. The type of the genus is N. maculatus, Theobald.
Three are malaria carriers (vide list, p.566).
Genus. Cellia, Theobald.
“Mono. Culicid.,” 1903, iii, p.107; 1910, v, p.67.
Very marked Anophelines, with densely scaly abdomens, the scales irregularly disposed on the dorsum and forming dense lateral tufts; thorax with flat spindle-shaped scales; palpi densely scaled and also the wings.
The type of the genus is the African C. pharoensis, Theob. It is represented in Asia by C. kochii, DÖnitz; in West Indies and South America by C. argyrotarsis, Desvoidy, and C. bigotii, Theob.; in Africa by C. squamosa, Theob., etc.
C. argyrotarsis, Desvoidy, and C. albimana, Wiedemann, are undoubtedly malaria bearers.
Genus. Neocellia, Theobald.
“Mono. Culicid.,” 1907, iv, p.111.
Allied to Cellia, but has no lateral scale tufts. Three species recorded from India.
Genus. KertÉszia, Theobald.
“Ann. Mus. Nat., Hung.,” 1905, iii, p.66.
This genus has the thoracic scales hair-like, except a few narrow curved ones in front; abdominal scales long, broad and irregular.
A single species, K. boliviensis, Theob. from Bolivia.
Genus. Manguinhosia, Cruz.
The thorax has narrow hair-like curved scales and some broad straight scales; others spatulate on the sides. Abdomen with fine hairs, except the last three segments which are scaly. Tufts of scales on the hind femora. Wing scales lanceolate.
The type is M. lutzi, Cruz, from Brazil.
Genus. Chagasia, Cruz.
“Brazil-Medico,” 1906, xx, pp.20, 199.
This genus can at once be told by the antennal segments having many dense scaly tufts. Type, C. fajardoi, Lutz, from Brazil.
Genus. Calvertina, Ludlow.
Canadian Entomologist, 1909, xli, pp.22, 234.
The antennÆ in this genus have outstanding scales on the second segment, more appressed ones on the first. At least one abdominal segment with long, flat, more or less spatulate scales. Type, C. lineata, Ludlow, from Philippine Islands.
Genus. BirÓnella, Theobald.
“Ann. Mus. Nat. Hung.,” 1905, iii, p.69.
At once told by the first submarginal cell being very small. Type, B. gracilis, Theob. from New Guinea.
Sub-family. MegarhininÆ.
Three genera occur in this marked sub-family; they are the largest of all mosquitoes, and are very brilliantly coloured, and many have tail fans. They occur in North and South America, Asia, Africa, and Australia. The long curved proboscis is very marked. They are usually spoken of as elephant mosquitoes; some are vicious blood-suckers at times.
The three genera tabulate as follows:—
| a. | Palpi long in both sexes. | |
| . | Last segment of ? palp round or blunt as if broken | Genus Megarhinus, R. Desvoidy. |
| . | Last segment of ? palp long and pointed | Genus Ankylorhynchus, Lutz. |
| aa. | Palpi of female short of male long. Palpi of female not more than one-third length of proboscis | Genus Toxorhynchites, Theobald. |
Genus. Megarhinus, Robineau Desvoidy.
“MÉm. Soc. d’Hist. nat. de Paris,” 1827, iii, p.412; “Mono. Culicid.,” 1901, i, p.215; 1903, iv, p.163; 1907, iv, p.128; 1910, v, p.89.
All large brilliant mosquitoes with long palpi in both sexes and, as a rule, with a caudal fan of scales; the proboscis is long and bent. They are all sylvan species, and are not so far recorded as biting man.
Genus. Toxorhynchites, Theobald.
“Mono. Culicid.,” 1901, i, p.244; 1903, iii, p.119; 1907, iv, p.140; 1910, v, p.95.
Differs from the former genus in that the female palpi are short. The palpi may have one, two or three minute terminal segments. Banks’s genus Worcesteria has three.
The elephant mosquito of India (T. immisericors), Walker, bites very severely. They are sylvan species.
Sub-family. CulicinÆ.
Genus. Mucidus, Theobald.
“Mono. Culicid.,” 1901, i, p.268; 1910, v, p.125.
This genus is so far confined to Australia, West and Central Africa, India, East Indies and Malay Peninsula. They are all large mosquitoes, easily told by the whole body being more or less covered with long twisted scales, giving them a mouldy appearance, and the legs densely scaled with outstanding scales; the wings with large parti-coloured scales. The Australian M. alternans, Walker, occurs in larval form both in fresh and salt water. The adults bite man.
Genus. Psorophora, Robineau Desvoidy.
“MÉm. de la Soc. d’Hist. nat. de Paris,” 1827, iii, p.412, R. Desvoidy; “Mono. Culicid.,” 1901, i, p.259; 1903, iii, p.130; 1907, iv, p.158; 1910, v, p.123, Theobald.
This genus is confined to the Americas and the West Indies. Several species exist which can easily be told from Mucidus by the absence of long twisted scales and the narrower wing scales. The legs are densely scaled and the thorax ornamented with flat spindle-shaped scales.
P. ciliata, Robineau Desvoidy, occurs in both North and South America, and bites man.
Genus. Janthinosoma, Arribalzaga.
“Dipt. Arg.,” 1891, p.52, Arribalzaga; “Mono. Culicid.,” 1901, i, p.253; 1903, iii, p.124; 1907, iv, p.152; and 1910, v, p.118, Theobald.
Hind legs only densely scaled; some of the hind tarsi are always white. The venation is as in Culex. The abdomen is metallic and iridescent. They all bite man and occur only in the Americas and West Indies.
Genus. Stegomyia, Theobald.
“Mono. Culicid.,” 1901, i, p.283; 1903, iii, p.130; 1907, iv, p.170; 1910, v, p.151.
This, the most important genus in the CulicinÆ, can be told by the head and scutellum being clothed with flat scales and the thorax with narrow curved ones.
About forty species are known in this genus, occurring in Southern Europe, Asia, Africa, Australia, the Americas, East and West Indies, and on most oceanic islands. Many of them seem to be vicious blood-suckers. They are mostly black and white mosquitoes, and several seem to go by the name of tiger mosquitoes. The genus contains the yellow fever mosquito (S. fasciata, Fabricius), the only one that need be dealt with in detail here. The chief known species tabulate as follows:—
| A. | Proboscis banded. | |
| a. | Legs basally banded. | |
| Thorax brown, with scattered creamy-white scales | annulirostris, Theobald. | |
| Thorax black, with narrow, curved golden scales | periskelta, Giles. | |
| aa. | Legs with basal and apical banding. Fore legs with no bands; mid with apical and basal bands on first and second tarsals, hind with basal bands. | |
| Thorax white in front, with a brown eye-like spot on each side | thomsoni, Theobald. | |
| AA. | Proboscis unbanded. | |
| . | Legs basally banded. | |
| ?. | Abdomen basally banded. | |
| Thorax with one median silvery-white line | scutellaris, Walker. | |
| Thorax as above, but pleurÆ with white lines | pseudoscutellaris, Theobald. | |
| Thorax similar, but two white spots near where line ends | gelebinensis, Theobald. | |
| Thorax with two median yellow lines and lateral curved silvery lines | fasciata, Fabr. | |
| Thorax with two short median lines and a white patch on each side | nigeria, Theobald. | |
| Thorax with large lateral white spots in front, smaller ones by wings, two narrow median lines and two posterior sub-median white lines | lilii, Theobald. | |
| Thorax with a white W-shaped area in front, a prolongation curved on each side enclosing a brown eye-like spot | W-alba, Theobald. | |
| Thorax with white frontal median spot, two large lateral spots, a small one in front of the wings, a narrow median white line and narrow sub-median ones on posterior half. Last two hind tarsi white | wellmannii, Theobald. | |
| Thorax brown, with broad white line in front extending laterally towards wings, where they swell into a large patch, a white line on each side just past wing roots. Last two hind tarsi white | albipes, Theobald. | |
| Thorax with silvery white spot on each side in front, small one over roots of wings and white over their base. Last two hind tarsi white | pseudonigeria, Theobald. | |
| Thorax with two lateral white spots, front ones the largest, a small median one near head, two yellow median lines, a short silvery one on each side before the scutellum | simpsoni, Theobald. | |
| Thorax with silvery-white scaled area in front and another on each side in front of wings | argenteomaculata, Theobald. | |
| Thorax with median yellowish-white line, a silvery patch on each side in front of wings extending as a fine yellow line to the scutellum, and another silvery spot before base of each wing | poweri, Theobald. | |
| Thorax with small grey-scaled area in front of wing roots and three short creamy lines behind | minutissima, Theobald. | |
| Thorax (?) denuded; abdomen black; fifth segment with yellow basal band; sixth unbanded; seventh, two median lateral white spots; eighth, two basal lateral white spots; second hind tarsal nearly all white | dubia, Theobald. | |
| ??. | Abdomen unbanded. | |
| First hind tarsal all white, second basally white, last two dark. Thorax chestnut brown, with a broad patch of white scales on each side in front and a median pale line | terreus, Walker. | |
| . | Legs with white lines as well as basal bands. | |
| Thorax brown, with white lines; abdomen with basal bands | grantii, Theobald. | |
| . | Fore and mid legs with apical bands, hind basal. | |
| Fourth tarsal of hind legs nearly all white | mediopunctata, Theobald. | |
| Mid metatarsi with basal pale banding, base and apex of hind, also base of first tarsal pale | assamensis, Theobald. | |
| . | Legs unbanded. | |
| d. | Abdomen basally banded. | |
| Thorax with front half white, rest bronzy-brown | pseudonivea, Ludlow. | |
| Thorax deep brown, with scattered golden scales, showing two dark eye-like spots; head white, dark on each side and behind | albocephala, Theobald. | |
| Thorax brown with golden stripes; abdomen with narrow basal bands on fifth and sixth segments only | auriostriata, Banks. | |
| dd. | Abdominal banding indistinct. | |
| Thorax with broad silvery white patch on each side in front | albolateralis, Theobald. | |
| ddd. | Abdomen unbanded. | |
| Thorax with six silvery spots | argenteopunctata, Theobald. | |
| dddd. | Abdomen with apical white lateral spots. | |
| Thorax unadorned, except for pale scaled lines laterally | punctolateralis, Theobald. | |
| ddddd. | Abdomen with basal white lateral spots. | |
| Thorax with two pale median parallel lines and two silvery lateral spots | ininuta, Theobald. | |
| Thorax unadorned. | ||
| A white spot middle of head | tripunctata, Theobald. | |
| No white spot | amesii, Ludlow. | |
| AAA. | Proboscis yellow basally, dark apically. | |
| Abdomen with apical pale bands | crassipes, Van der Wulp. | |
| AAAA. | Proboscis with median interrupted white line on basal half. | |
| Head black, anterior margin grey | albomarginata, Newstead. |
Stegomyia fasciata, Fabricius (Yellow Fever Mosquito).
This insect, which is the proven carrier of yellow fever, is commonly called the tiger, brindled, spotted day or striped mosquito. It is also referred to by some writers as S. calopus, Meigen. It is subject to considerable variation in colour, but the thoracic markings are generally very constant. The general colour is almost black to deep brown, the head with a median white area, white at the sides and in front around the eyes; the thorax has two median parallel yellow lines, a broad curved silvery one on each side and white spots at the sides; the scales on the intervening spaces of the thorax are brown. The dark abdomen has basal white bands and basal white lateral spots. The dark legs have basal white bands, the last segment of the hind legs being all white except in a variety from South America and the West Indies (luciensis), which has the tip of the last hind tarsal dark. The abdomen may also vary in colour, some having pale scales over most of the surface (queenslandensis).
The food of the adult female consists mainly of man’s blood, but she will also feed on dogs and other animals. The male has been said to bite, but such is very unusual. This mosquito bites mainly in the daytime up till about 5p.m.
The adults breed the first day after emergence. They may live a considerable time, Bancroft having kept females for two months in confinement. The ova are laid separately, often in chains; they are black, oval, with a reticulated membrane outside, some of the reticulated cells containing air. They may hatch in from six to twenty hours, the larval stage nine days, the pupal stage three; thus the whole cycle may be completed in from twelve to thirteen days. The ova when dry can remain undeveloped for a considerable time. The larvÆ are greyish-white, with short, thick siphon, and feed at the bottom of the water, only coming to the surface now and again to breathe. This is almost entirely a domesticated gnat, seldom being found far from man’s habitations. Its larvÆ occur in such small collections of water as old sardine tins, jam-pots, calabashes, puddles, barrels, wells—in fact, wherever water is held up, even to the gutters of houses. Not only are they found breeding on land, but also on board ship, although they prefer artificial collections of water. They may also breed in larger natural collections.
This insect is easily transported by steam and sailing ships and by train, and this doubtless explains its very wide distribution. The adults may live for fifty days, and it is on this account and their frequent occurrence on ships that danger lies in regard to the Panama Canal. An infected insect may leave that endemic centre of yellow fever and live until the vessel arrived at the Philippine Islands and fly ashore, and so introduce the disease for the native fasciata possibly to spread.
Roughly the distribution of this pest is as follows: Africa from South to North, but especially along the coast and up the Nile. In Asia, in India, Ceylon, Burma, Siam, along the ports of the Malay Peninsula, in French Cochin China, Philippine Islands, the Andaman and Nicobar Islands, Japan, Malay Archipelago, and East Indies, Turkey in Asia, Arabia and Palestine.
In Australia it occurs in Queensland, New South Wales, Victoria and South Australia.
In Europe in Italy, Spain, Portugal, Greece, in the Mediterranean Islands.
In South America, Central America, Mexico, North America, and the West Indies it is very abundant, and it also is found in the Bahama Islands, Fiji, Sandwich Islands, Samoa, the Azores, Teneriffe and Santa Cruz, Pitcairn Islands and Bermuda.
For a full account of its distribution the reader is referred to the following: “The Distribution of the Yellow Fever Mosquito (Stegomyia fasciata, Fabricius)
Stegomyia scutellaris, Walker.
A vicious biter, found in India, China, Malay, East Indies, and Ceylon. The thorax has one median silvery stripe, and so can easily be told from S. fasciata.
A very similar species occurs in Fiji, but can be told by the pleurÆ having white lines, not spots (S. pseudoscutellaris, Theobald). It is the intermediate host of filaria in Fiji (Bahr).
A number of nearly allied genera occur here (vide synoptic table).
Genus. Theobaldia, Neveu-Lemaire.
Theobaldinella, Blanchard.
Includes several large Culicines, of which T. annulata, Meigen, is the type. The wings are usually spotted (annulata, incidens, etc.), but may be nearly plain (spathipalpis). The males have the palpi swollen apically, and the females have long five-jointed palps.
Several of these are vicious biters.
Theobaldia annulata, Meigen.
This large gnat (6mm. long) can be told by its wings having five large spots of dark scales and by its legs having broad basal white bands to the tarsi. The larvÆ occur in rain barrels and small pools. It is essentially a domestic form, occurring in houses and privies. Its distribution is Europe generally and North America. The bite is very severe, and in some districts gives rise to painful oedema.392
Theobaldia spathipalpis, Rondani, occurs in Italy, Mediterranean Islands, Palestine, the Himalayas, Khartoum, and in South Africa. It is about the same size as T. annulata, but is yellowish-brown in colour, with striped thorax and mottled and banded legs. It occurs in privies and bites very severely.
Genus. Culex, LinnÆus.
“Syst. Nat. Ed.,” 1758, x, LinnÆus; “Mono. Culicid.,” 1901, i, p.326; 1910, v, p.322, Theobald.
Fig. 400.—Wing of a Culex.
This large genus still contains many forms which should be excluded. The species normally have narrow curved median head-scales, and similar ones on the scutellum; the female palpi are shorter than in the former genus and the male palpi are pointed; the lateral vein-scales are narrow and linear.
The type is Culex pipiens, Linn., the common gnat of Europe. The thorax is covered with narrow curved golden-brown scales, the abdomen has basal pale bands to the segments and the legs and proboscis are unbanded. The stem of the first submarginal cell is always less than one-fifth the length of the cell. It lays its eggs in rafts in water-butts, etc., and even in the foulest water. They are first deposited in England in June and July, and again soon after hatching in August. In some districts this gnat bites man viciously, in others not at all.
The common tropical gnat (Culex fatigans, Wied). This resembles the European Culex pipiens, but can always be told by the stem of the first submarginal cell always being much longer than it is in C. pipiens. This is one of the species that has been proved to transmit filariÆ to man, etc. Varieties of it occur in almost every country between 40° N. and S., having a very similar range to S. fasciata. In all countries it appears to be connected with the transmission of Filaria bancrofti, and it is also said to carry the micrococcus of dengue fever.
Genus. Melanoconion, Theobald.
“Mono. Culicid.,” 1903, iii, p.238; 1907, iv, p.507; 1910, v, p.455.
This genus is composed of eight species, most of which are small black gnats which bite viciously and which occur in swamps and jungles. They can at once be told from Culex by the veins of the wings having dense broadened scales on their apical areas and along the upper costal border. The femora and apices of the tibiÆ are swollen.
The black mosquito, Melanoconion atratus, Theob. This small gnat is a very troublesome pest in swamps in the West Indies. The female bites both by day and by night, and the bite causes severe irritation. The larvÆ live in permanent ponds. It is almost black in colour, but sometimes presents a dull coppery sheen; each segment has small lateral basal white spots. Length 2·5 to 3mm.
It occurs in Para and British Guiana as well as in the West Indies.
Ordinary mosquito netting is no use for keeping off this pest.
Genus. Grabhamia, Theobald.
“Mono. Culicid.,” 1903, iii, p.243; 1907, iv, p.284; and 1910, v, p.277.
Allied to Culex, but separated by the wings having short fork-cells, mottled scales, the median ones thick and also some of the lateral ones short and broad; the last two joints of the male palps are very slightly swollen. The eggs are laid singly, not in rafts, and the larvÆ have short, thick siphons. Ten species occur and are found in Europe, North America, West Indies and Natal. G. dorsalis, Meigen, bites severely in Europe. G. sollicitans, Walker, is a great scourge along the New Jersey Coast and at Virginia summer resorts and in Florida. It breeds in brackish water and is the most common mosquito of the Atlantic seaboard.
Genus. PseudotÆniorhynchus, Theobald;
TÆniorhynchus, Theobald, non-Arribalzaga.
Differs from the former in having the whole wing veins clothed with dense, broadish elongated scales. They occur in South America (T. fasciolatus, Arri.), in Africa (T. tenax, Theob.), in Europe (T. richardii, Ficalbi). The latter bites very severely.
Genus. TÆniorhynchus, Arribalzaga; Mansonia, Blanchard;
Panoplites, Theobald.
Compt. rend. heb. Soc. Biol., 1901, iii, 37, p.1046; “Mono. Culicid.,” 1901, ii, p.173; and 1910, v, p.446, Theobald.
A very marked genus, easily told by the broad asymmetrical wing scales. It occurs in Africa (T. africana and T. major, Theob.); in Asia (T. uniformis, Theob.; T. annulipes, Walker, etc.) and in Australia (T. australiensis); in the Americas and West Indies (T. titillans, Walker). The eggs (fig.395, d) are peculiar in form and are laid separately; the larva has not been described; the pupa has long curved siphons. They mostly occur along rivers, in swamps and forests, and bite very severely. They also enter houses (T. titillans). T. uniformis is most troublesome during the rains. The saliva is strongly acid. Both these species carry the larvÆ of Filaria bancrofti.
Genus. Chrysoconops, Goeldi.
“Os Mosq. no Para,” 1905, p.114, Goeldi; “Mono. Culicid.,” 1910, v, p.433, Theobald.
Bright yellow or yellow and purple mosquitoes, with rather dense wing scales. Numerous species occur in Africa (aurites, annettii, fuscopennatus, etc.), others in India, Australia and South America.
Low found filariÆ in the thoracic muscles of fuscopennatus in Uganda.
Several of the Ædeomyina bite, especially the small UranotÆnias. They are all sylvan species, seldom entering houses. They need not, therefore, be referred to here.
For full details of the Culicid genera and species the reader is referred to my monograph393 and other works mentioned below.
Other Nematocera.
Other nematocerous flies are midges, daddy-long-legs and sand-flies. The ones which cause annoyance to man besides CulicidÆ are the following:—
Sand-flies (SimulidÆ), certain midges (ChironomidÆ), and a few owl midges (PsychodidÆ).
The Nematocera have long thread-like jointed antennÆ and their pupÆ are, as a rule, naked; the larvÆ have a distinct head and can thus be told from the next section (Brachycera).
Family. SimulidÆ.
This family consists of a single genus, Simulium, Latreille, which Roubaud has recently divided into two sub-genera called Pro-Simulium and Eu-Simulium. These insects, which are frequently spoken of as sand-flies, are found in all parts of the world; they are all small insects varying from 1·5 to 3mm. The females are very bloodthirsty, but the males appear to be incapable of sucking blood.
The head sunk under the humped thorax; antennÆ short, straight; palpi short
SimulidÆ often occur in swarms, and attack not only man but cattle, horses, and poultry. In some districts they are more annoying than mosquitoes.
Their life-cycle has been most completely worked out by King, in Africa.
The larvÆ and pupÆ occur in swiftly flowing water, by waterfalls, in rapids, etc. The ova are laid in gelatinous masses on plants or rocks close to or overhanging the water. The larva is cylindrical, enlarged posteriorly, where it is provided with a sucker, by means of which it attaches itself to a rock, water weeds, debris, etc.; anteriorly it has a proleg close behind the head on the lower surface. The head is dark and chitinous. The respiration takes place by means of branched tracheal gills which protrude from the dorsal surface of the last body segment; they are retractile. The colour varies from deep green to yellow or almost black. Their food consists of algÆ and other organisms in the water brought to their mouth by two fan-like organs placed on the head. The larvÆ can crawl from place to place by means of the thoracic proleg; they occur in masses, usually in a more or less erect attitude. A network of threads is spun on their support, by means of which King tells us “they are enabled to maintain their position against the strongest current; frequently they will leave their support and let themselves out into the stream anchored by threads of silk and enabled by them to return.”
When full fed the larva spins a pocket-shaped cocoon on the support, within which it pupates. The pupa is motionless and has a pair of branched spiracles projecting from behind the head. When the adult emerges, a bubble of air collects around it, and in this it floats to the surface and at once takes wing. The European species take a month to complete larval life, a week being spent in the pupal stage. The flies are most restless, and even when stationary continually move their legs about like feelers. Sometimes the swarms consist entirely of females, sometimes early in the season mostly of males.
The females pierce the skin of humans on tender spots, such as ears, the forehead, around the eyes and nose, and crawl into the cavities. They are quite harmless at night, mainly attacking about sunrise and sunset. Some crawl up the arms and legs and down the neck, and leave behind little red weals which itch intensely (S. damnosum, Theob.), and blood may flow freely from the wounds.
The following are some of the worst species:—
Simulium columbaschensis, the “Kolumbatz fly,” which abounds in the damp marshy lands along the Danube, and is a great plague to man and beasts in Hungary, and is also abundant in Austria and Moravia, and is most numerous after inundations from the Danube. They sometimes appear in such swarms that it is impossible to breathe without getting them into one’s mouth. There are instances of children being killed by these flies when left on the ground by their mothers when working in the fields.
S. damnosum, Theob. This occurs throughout Equatorial Africa and is known as the “jinja fly” in Uganda, the “fouron” in the French Congo, the “kilteb” in the Sudan. It is a most vicious biter, and in some parts occurs in “belts”; Dr. Christy found one such extending from the shores of the Victoria Nyanza northwards along the right bank of the Nile for twelve or fifteen miles or more, and perhaps three or four miles wide. In this area the flies swarm in millions at certain
S. griseicollis, Becker. The so-called “nimitti” occurs in Upper Egypt and the Anglo-Egyptian Sudan. It lives near the river and is not found more than half a mile from it. Human beings are bitten on the face and hands, animals in the region of the pudenda.
S. latipes, Meigen. This is a European species, also found in Natal.
S. wellmanni, Roubaud. The “ohomono” of Angola, where it bites viciously and is dreaded by the naked porters.
S. buissoni, Roubaud. Occurs in abundance in the Marquesas Islands. It has been suggested that this species may help to propagate leprosy.394
A large number of these insects have been described by Lutz in Brazil.395
A Simulium sp. (?) is very harmful to poultry in Cape Colony.396
In America, SimulidÆ are most annoying. One, S. meridionale, Riley, also known as the turkey gnat in the Mississippi Valley, has been supposed to be the carrier of chicken cholera; anyhow, it has caused the death of thousands of chickens and turkeys in Virginia annually.397
In Mexico Townsend found a Simulium which was named S. occidentalis, which caused great annoyance to man, many people being so susceptible to them as to preserve through the gnat season a chronic inflammation of the exposed parts of face and neck, resulting from the repeated bites giving rise to sores.398
Men and horses have been partially incapacitated by the bites of sand-flies or Simulium in a Hampshire wood (Cantlie, Brit. Med. Journ., April 28, 1900, v, No. 2,052, p.1023).
Fig. 401.—Wing of Simulium.
Fig. 402.—Wing of Chironomus.
Family. ChironomidÆ (Midges).
The ChironomidÆ or midges are not only frequently mistaken for mosquitoes, but some are very annoying to man by biting him as mosquitoes do. They are easily distinguished from true mosquitoes (CulicidÆ) by the following characters: (1) head small, often retracted under the cowl-like thorax; (2) no scales to the wings or body; and (3) the different arrangement of veins on the wings (fig.402).
Two genera are important as annoying man, namely, Culicoides, Latreille, and Johannseniella, Williston. The larvÆ of ChironomidÆ are either aquatic, both fresh water and marine, and help to make the former foul,399 according to Slater, or may, as in CeratopogoninÆ, live beneath the bark of trees, etc. The pupÆ are very varied and also the life-histories of the different genera.400 The blood-sucking habit is confined to the sub-family CeratopogoninÆ.
Sub-family. CeratopogoninÆ.
This sub-family of midges consists of very small species varying from 1 to 2mm. in length; the wings have darkened areas, and the second longitudinal vein is wanting, and the first and third veins are stouter than the others and placed close to the anterior margin, the fourth and fifth are forked; the antennÆ in both male and female are composed of fourteen segments, six or eight in the males bearing long hairs.
The chief blood-sucking species belong to the genera Culicoides, Latreille, and Johannseniella, Williston. The latter genus differs from the former in the absence of an empodium or median appendage on the last segment of the tarsi. The genus Ceratopogon, as restricted by Kieffer, is not supposed to take vertebrate blood, but Austen has recently noticed that the type specimen of C. castaneus, Walker, and a new species described by him, apparently have their bodies distended with blood. The wings in the CeratopogoninÆ are carried flat when at rest.
Fig. 403.—A Ceratopogon, or midge. Greatly enlarged.
In spite of their small size the females are the most bloodthirsty and annoying of all insects. The Culicoides, which are often called “sand-flies,” bite during the day and rarely at night. Usually they are most troublesome between 3 and 6p.m. They frequently attack in swarms, especially in the open, and owing to their minute size can get through fine mosquito netting. Some of them produce a distinct “buzz” when on the wing. These insects are found in all parts of the world. No species has been definitely connected with any disease, but Culicoides has been suspected of carrying the germs of Delhi boil. The larvÆ of Culicoides are elongate in form and have smooth bodies composed of thirteen segments including the head, which is horny; there is no proleg on the first segment as seen in Chironomus, and on the anal segment are retractile gills. They are very active and live in the sap of various trees which saturates diseased bark.
The pupÆ are smooth, but the abdominal segments bear a transverse row of small spines. Austen describes a number of Culicoides and one Johannseniella and three Ceratopogons from Africa,401 and Lutz402 a number of this sub-family from Brazil,
Culicoides ornatus, Taylor, is described from Townsville, Australia, found in mangrove swamps. It is a very vicious biter and causes considerable irritation, settling on hands and wrists (Taylor, Rep. Ent. Aust. Inst. Trop. Med. (1912), 1913, p.24).
Family. PsychodidÆ (Owl Midges).
This family of diptera is of considerable importance, not only on account of the blood-sucking habits of some species, but especially on account of one at least having been proved to be the carrying agent of “papataci” fever, a three-day fever very prevalent in Malta and several parts of Southern Europe in the autumn.
It is also possible that these small flies are connected with the formation of “Delhi boil,” caused by a protozoan parasite.
Fig. 404.—An owl midge, Phlebotomus sp. Greatly enlarged. (From Giles’s “Gnats or Mosquitoes.”)
PsychodidÆ are all very small flies, many of which have a moth-like appearance, and owing to their fluffy nature are spoken of in Britain as “owl flies,” sometimes also as “window flies.” Their bodies and wings are covered with hairs, densely in some (sub-family PsychodinÆ), and in a few with patches of flat squamÆ. In the non-blood-sucking PsychodinÆ the wings are carried in a peculiar manner downwards over the body, to a slight extent resembling the HepialidÆ, or swift moths. The wings may be ovoid or lanceolate, and have a marked venation as seen in the figure. The proboscis is short and non-suctorial in the majority of genera, but in the sub-family PhlebotominÆ it is elongated and hard. The antennÆ are long and of sixteen segments, and bear whorls of fine hair.
There are two sub-families, PsychodinÆ and PhlebotominÆ; in the former the mouth is not suctorial; the female has a horny ovipositor and the second longitudinal vein is branched at the root of the wing; in the second sub-family the proboscis may be formed for sucking, the female has no horny ovipositor, and the second long vein has its first fork near the middle of the wing.
The sub-family PhlebotominÆ contains the genus Phlebotomus, which occurs in South Europe, South Asia, Africa, North and South tropical America. They are all small grey, brown, or dull yellow-coloured flies, and carry their wings when at rest upwards like a butterfly. The proboscis is moderately long and the legs long and thin.
The females are most vicious blood-suckers, but in some species anyhow the
The life-cycle has been worked out by Newstead403 and Grassi404 in Europe, and by Howlett405 in India.
The larvÆ have been found in crevices in rocks and caves, in dirty cellars, and dark damp places containing rubbish, and are also said to live in crevices in the walls of privies and cesspits.
The minute larva is very marked; as figured by Newstead it has two long chÆtÆ projecting upwards, in some stages branched, in others simple, and on the segments a few blunt spine-like processes. The pupÆ are found in similar situations. The ova are very minute, elongate, translucent white, and covered with a thin coating of viscous matter when first laid; soon after they become dark brown, shiny, with long black wavy lines. Newstead found the incubation period in Malta to last for about nine days in P. papatacii. Five species are known in Europe, five in Africa,406 two in North America, and eight are described by Annandale407 in the Oriental region. Lutz and Neiva have described three species from Brazil408 (P. longipalpis, intermedius and squamiventris).
Brachycera (Flies).
The antennÆ as a rule have three segments, and are usually shorter than the head. The first segment of the antennÆ is frequently very small, and the third one is generally the largest, and sometimes possesses a terminal annulated bristle. The palpi have from one to three segments; the mandibles are covered by the labium. The three thoracic rings are coalesced; wings are almost always present, the posterior ones being rudimentary and covered with a little scale. From the ova legless maggots are hatched, which as a rule have not a distinct head, but occasionally possess two claw-like hooklets. These maggots live in decomposing organic matter; they rarely live in water and some of them are parasitic. They either become barrel-shaped pupÆ within the last larval integument or, after casting it, are transformed into naked pupÆ. The larvÆ of numerous Brachycera have been observed in man, some in ulcers or on mucous membranes, others in the skin or in the intestine, etc. In many cases the report only mentions the presence of the larvÆ of flies; in other cases the species has been determined; whilst in still other cases the corresponding adult creature is unknown. We must therefore confine ourselves to describing the most common varieties.
Family. PhoridÆ.
These flies belong to the same division of Diptera, the Aschiza, as the family SyrphidÆ or “hover flies.” They are all small insects with marked antennÆ and wings; the former have the third segment globular and enlarged, and thus hiding the first two; the wings are short and broad, the venation shows two short, thick, long veins with four thin ones running out from them. The larvÆ normally live in decaying animal and vegetable matter, but one species, AphiochÆta ferruginea, Brun., has been found as an intestinal parasite of man.
AphiochÆta ferruginea, Brun.
This small fly belonging to this family is of an orange-ochreous colour, the upper part of the thorax tawny, and with dark bands on the abdomen, legs pale yellow, the hind femora tipped with dark brown. It measures only 2 to 3mm. in length. This insect is shown by Austen to be widely distributed in the tropics, being found in India, Burma, West Africa, and Central America. The larvÆ breed in decaying animal matter, such as putrid meat, decomposing shell-fish, etc.
Heusner bred out sixty-three flies from larvÆ taken from an Indian’s foot.
Baker (Proc. Burma Branch Brit. Med. Assoc., 1891, p.11–16) found that the maggots of this fly were passed per anum by a European at intervals during a period of ten months. Baker found that the larvÆ fed on human fÆces; from the egg stage to the deposition of eggs from the resultant brood of flies occupied twenty-two days. He concludes that they are capable of propagating, and do so while living within the human intestines. He also records the larvÆ in two girls.
The larva does not seem to have been described, but Austen describes the pupa (Trans. Soc. Trop. Med. and Hyg., iii, No. 5, p.229).
Phora rufipes, Meig.
The larvÆ of the “hump-backed fly” live in rotting potatoes, mushrooms, radishes, etc., and when accidentally introduced into the intestine of man can, like other larvÆ, live there twenty-four hours and even more, and may set up serious gastric disturbances.
P. rufipes is the same as P. pallipes, Latr.
Family. SepsidÆ.
Small blackish flies, elongate, with abdomen narrowed at the base, thickened and curved downwards towards the extremity. LarvÆ often found in decaying vegetables, ham, cheese, etc. The larvae have the power of skipping; conical in form, pointed in front, truncated behind, about 5mm. long, shiny and smooth, the anal segment with fleshy protuberances. The genus Piophila has a short proboscis and the cross-veins of the wings approximate.
Piophila casei, L.
Cheese flies. The larvÆ live in ripe cheese, with which they are sometimes introduced into human beings (Meschede).
The larvÆ of the cheese flies (Piophila casei) may pass through the alimentary canal of human beings alive, and have been occasionally referred to in cases of internal myiasis. It also breeds in dead bodies in adipose tissue. Howard records it on human excrement. It is thus possible that some of the recorded cases of this pest being passed alive may be due to eggs deposited on human fÆces.
Family. SyrphidÆ (Hover and Drone Flies).
Amongst the large family of SyrphidÆ is found a section known as the EristalinÆ or drone flies, whose curious long-tailed larvÆ are popularly called “rat-tail larvÆ,” on account of the end of the body being drawn out into a long telescopic tail of two segments, at the end of which are placed the breathing pores. These larvÆ
Family. DrosophilidÆ.
Small, rather plump flies, with short, broad abdomen, with bristles on the head and legs. Often abundant in decomposing fruit, and may occur in dense masses.
Drosophila melanogaster, Br.
The larvÆ of this fly occur in over-ripe fruit and in fungi, often also in human habitations, and live in substances undergoing acid fermentation (vinegar, decaying fungi, rotting fruit, in damaged spots in diseased trees), much more rarely in animal substances, and they occasionally gain access to the human intestine (for example, by the medium of sour milk). When introduced in any quantity, they cause vomiting or attacks resembling colic; when taken in the pupal stage no unpleasant results are produced.
Family. MuscidÆ.
Teichomyza fusca, Macq.
Syn.: Scatella urinaria, Rob. Desv.; Ephydra longipennis, Meigen.
The larvÆ live in the urine in privies. Several authors state they have found them in fresh fÆces or in vomited matter. Pruvot states that they continue for three days in the stomach of rats into which they have been intentionally introduced. (Pruvot, G., “Contrib. À l’Étude des larves de dipt, trouv. dans le corps humain,” ThÈse de Par., 1882; Chatin, J., in Comp. rend. Soc. de Biol., Paris, 1888 (8), v, p. 396; Roger, H., ibid., 1851 (1), iii, pp.88, etc.)
Homalomyia canicularis, L., etc.
Fig. 405.—Larva of Homalomyia canicularis. Enlarged.
Homalomyia manicata, Meig., live as larvÆ in decomposing vegetable matter or in cultivated vegetables (cabbage); they are easily recognizable by their plumed bristles, which are situated laterally on the body segments. They obtain access fairly often to the human intestine and give rise to very uncomfortable symptoms. Cases have been recorded from Germany, Austria, France, England, North America (Wacker, in Artzl. Intelligenzbl., 1883, xxx, p.109; Florentin, in Compt. rend. Soc. de Biol., Paris, 1904, lvi, p.525; and other authors).
The larvÆ of an allied genus (Anthomyia), which, however, does not possess plumed bristles, has been found in the external auditory meatus of a man (A. pluvialis, according to Danthon).
[H. canicularis is common to Europe and North America, and is an abundant house-fly. It is the small house-fly so often seen on windows. Besides living on vegetable matter, they have also been found in the nests of the humble bee. LarvÆ of this species (fig.405) were sent to the British Museum, taken from the fÆces of
Homalomyia scalaris, Fabr.
[This is not a synonym of the above, but a distinct species.
[H. manicata, Meigen, is also distinct.—F.V.T.]
Anthomyia desjardensii, Macq.
This fly, allied to Homalomyia, is the cause of both intestinal and cutaneous myiasis at BihÉ, Angola (Wellman, Journ. Trop. Med. and Hyg., June, 1907, x, p.186).
HydrotÆa meteorica, L.
The larvÆ live in decaying vegetable substances, also in dung, and have been evacuated in some cases by man (Zetterstedt, Joseph).
Fig. 406.—LarvÆ of Calliphora vomitoria. Enlarged.
Fig. 407.—Larva of Chrysomyia macellaria. 4/1. (After Conil.)
Cyrtoneura stabulans.
LarvÆ in fungi, but occasionally also on larvÆ of butterflies and Hymenoptera; occasionally introduced into the human intestine (Joseph).
Musca domestica, L.,
and M. (Calliphora) vomitoria, L., and allied species; larvÆ of these have been repeatedly found in the intestine and nose of man (Mankiewicz, etc.).411
Musca domestica, Linn. (Common House-fly).
It is not only on account of a few larvÆ of the common house-fly (Musca domestica) being found in the intestines of man that it is of importance medically. It is far more important on account of the part it plays in the spread of diseases of the intestines, such as typhoid fever and cholera, infantile diarrhoea and dysentery.
Howard and Clark (Journ. Exp. Med., 1912, xvi, No. 6, pp.850–859) have shown that the house-fly is capable of carrying the virus of poliomyelitis for several days on the surface of the body and for several hours in the gastro-intestinal tract. The house-fly may also distribute the ova of TÆnia solium and the white worms (Oxyuris and Ascaris). It has also been proved that they may carry the germs of tuberculosis, and it is said that they play an important part in the spread of infectious ophthalmia in Egypt.
This insect is found in all parts of the world. In warm countries it breeds all the year round, and it may do so even in temperate climates in warm places, such as stove houses. Most, however, die off in the autumn; but some survive the winter as adults, in such places as kitchens, restaurants, and warm houses. I have never failed to find a few Musca domestica in houses during the winter. The majority, however, hibernate as puparia.
The females deposit from 120 to 150 eggs in a batch in stable manure, rotting vegetation, house refuse, spent hops, old soiled bedding, etc. A single female may lay as many as six batches of ova during her life. The eggs are shiny white, and hatch in from eight to twenty-four hours in warm weather to three or four days in cool weather. The white footless maggots are cylindrical, tapering to a point at the head end, truncated posteriorly. The head consists of two dark mandibular hooks and two short antennÆ. On the tail end are two plates, the stigmata, in which the main tracheal trunks open; in the second segment are a small pair of projecting stigmata. The larval stage lasts from seven to five days in hot weather; but in cold weather in temperate climes it may last six or eight weeks.
The larva on reaching maturity becomes a barrel-shaped puparium of a dark brown to black colour, and in this case changes to the pupa. This stage lasts from three days in the tropics to four or five weeks in cold weather, the life cycle thus varying from ten days in the tropics to fourteen in warm weather in Europe up to three or four months under unfavourable conditions.
All breeding grounds should be burnt or otherwise done away with, such as stable manure, house and kitchen refuse, human excrement and soiled substances, also decaying vegetation as soon as possible, certainly by every sixth day. Stable manure should be kept in closed receptacles and should be removed by every sixth day to at least one mile from habitations and sprinkled with chloride of lime. All kitchen and household refuse should be burnt at once or buried in pits and covered with soil. Latrines should be as far as possible from hospitals, mess rooms and tents. Food—especially milk, sugar and fruit—should be kept screened with muslin when house-flies are about. Mess rooms and tents and hospitals should have doors and windows screened with fine wire gauze during the fly season. All possible steps should be taken to prevent them contaminating man’s food and from breeding in human excrement and from entering hospitals. When present in dwelling-houses in numbers they may be killed by fumigation with pyrethrum or sulphur.
Genus. Chrysomyia, Rob. Desv.
Chrysomyia (Compsomyia) macellaria, Fabr.; Lucilia macellaria, Fabr.
Syn.: Lucilia hominivorax, Coq.; Calliphora infesta, Phil.; Calliphora anthropophaga, Conil.
A species distributed from the Argentine to the south of the United States which deposits its ova on ulcers, in the aural meatus or in the nasal cavities of persons who sleep in the open air. The larvÆ are yellowish white, 16mm. long, are armed with two strong mouth hooks, and provided with spinous rings (screw-worm); they lie hid in the nasal and frontal sinuses, in the pharynx, larynx, etc.; they perforate the mucous membranes, even cartilage, migrate into the eyes, the cranial cavity, middle ear, and cause severe disturbances; after the mature stage, in which the larvÆ leave the host to enter the pupal state, these symptoms often spontaneously abate after a lapse of eight days, leaving behind greater or less cicatrices, and consequently also defects in function of the organs attacked. Very often, however, sepsis sets in, usually with a fatal termination.
(Coquerel in: Arch. gÉn. de mÉd., 1858 (5), p.513; 1859, xiii, p.685; Ann. Soc. ent. France, 1858 (3), vi, p.171; 1859, vii, p.234. Weber in: Rec. de mÉm. de mÉd. milit., 1867 (3), xviii, p.159. Francius, A., in: Arch. f. path. Anat., 1868, xliii, p.98. Conil in: Bol. Acad. nac. cienc. Cordoba, 1881, iii, p.296. Humbert, Fr., in: Proc. U.S. Nat. Mus., 1883, vi, p.103; Amer. Nat., 1884, xviii, p.540. Lindsay in: Journ. Trop. Med., 1902; v, p.220, and other authors.)
Fig. 408.—The screw-worm fly (Chrysomyia macellaria).
[This species is known as the screw-worm fly. It attacks animals as well as man, especially laying its eggs on wounds formed by barbed wire. It may also be found on dead flesh. Dr. St. George Gray sent me specimens from St. Lucia, from
Chrysomyia viridula, Rob. Desv.
[This species is somewhat larger than the former; the body is metallic bluish-green, the dorsum of the thorax with three blackish, longitudinal stripes, and the face ochraceous; about 10mm. long. Austen records this species from man, Dr. Daniels having bred it from larvÆ from a sore on a human being in New Amsterdam, British Guiana. Dr. Laurence also bred it in Trinidad. In the latter case between 100 and 150 maggots were discharged from the nose of a woman suffering from facial myiasis (Brit. Med. Journ., January 9, 1909, p.88 + fig.).—F.V.T.]
Genus. Lucilia, Rob. Desv.
Lucilia nobilis, Meig.
The larvÆ were observed by Meinert in Copenhagen in the auditory meatus of a person who, after taking a bath, fell asleep in the open air, and on waking felt singing in the ears, and had a sensation as if there were water in the auditory canal. During the next days severe pains set in, and there was a discharge of blood and pus from both ears, as well as from the nose. On washing out the meatus the maggots made their appearance.
Lucilia cÆsar and L. sericata have also been observed in the larval state in man (Thompson, Hope, Henneberg and Calendoli, Napoli, 1907).
[This golden-green fly usually lays its eggs on decomposing organic matter; now and again it lays its eggs in wounds on man.—F.V.T.]
Genus. Pycnosoma, Brauer and v. Bergenstamm.
The species of this genus have a general resemblance to the Lucilias and Chrysomyias, but the body is stouter and the abdomen banded. The genus can be distinguished from Chrysomyia by the absence of the three thoracic stripes and by the eyes of the male, in which the facets forming the upper portion are much enlarged, whereas in Chrysomyia they are not noticeably larger. Austen also points out that the sterno-pleural bristles in Pycnosoma are 1:1, in Chrysomyia 2:1. The genus is found in tropical Asia and Africa only. All records of Chrysomyia (Compsomyia) in India must be referred to this genus. Bezzi and Stein (“Katalog der Palaarktischen Dipteren,” 1907, iii, p.543), however, regard the two as synonymous.
The larvÆ are frequently found in the nostrils of man and burrow into the sinus, but normally they live on decaying animal matter.
Pycnosoma forms the so-called Indian screw-worm. Patterson (Ind. Med. Gaz., October, 1909, xliv, No. 10) records the case of a woman at Tezpin, Assam, from whom as many as 100 larvÆ were removed at one time, and later the left orbital cavity was found packed with hundreds of maggots; eventually the patient died. It is possible that this, however, was due to a species of Sarcophaga. Austen undoubtedly records this genus causing nasal myiasis in India (Trans. Soc. Trop. Med. and Hyg., iii, p.235). At Dehra Doon, U.P., a woman discharged 100 larvÆ from her nose, with great pain in the nasal region and frontal sinuses.
The so-called “peenash,” a common malady in Rajputana, is a true nasal myiasis.
Genus. Sarcophaga, Mg.
Sarcophaga carnosa, L., 1758.
LarvÆ of flesh-flies provided with two claws at the anterior end, which settle on raw or cooked meat, and in the open on carcases of animals; they are often observed in man, both in the intestine (introduced with food) and in the nasal cavities, frontal sinus, conjunctiva, aural meatus, anus, vulva, vagina, prepuce, and open ulcers, often migrating further from the regions first attacked. (Gayot in Compt. rend. Acad. Sci., Paris, 1838, vii, p.125. Grube in Arch. f. Naturg., 1853, xix, 1, p.282. Legrand du Saulle in Compt. rend. Acad. Sci., Paris, 1857, xlv, p.600, and other authors.)
[This fly is viviparous. The fly varies from 10 to 30mm. in length, and is of a general ash-grey colour; the thorax with three dark stripes, the abdomen light grey with three black spots on each segment; legs black; base of wings yellow. It also attacks animals and birds, especially geese. The genus Sarcophaga is universally distributed. The maggots are whitish or yellowish footless larvÆ of twelve segments, tapering to a point in front, broadened posteriorly. There are two mouth hooks, by means of which they rasp their food. The breathing pores are at the end and consist of two groups of three slits, each surrounded by a hardened area. They pupate in their old skin, which turns brown.—F.V.T.]
Sarcophaga magnifica, Schiner, 1862.412
Syn.: Sarcophaga wohlfahrti, Portschinsky, 1875.
A species widely distributed over the whole of Europe, occurring especially in Russia (Mohilew); the presence of the larvÆ in man was first observed by Wohlfahrt (1768). The larvÆ settle in the pharynx, in the nose, the aural meatus, the conjunctiva, and in other regions of the human body; they also attack domestic animals and birds. As Portschinsky has shown, they cause severe inflammations, hÆmorrhages and suppurations in the organs in which they occur; children are especially attacked. A number of cases have been observed also in Central and Western Europe. [The fly has a light grey abdomen with shiny black spots which do not change their shape and appearance according to the angle in which the fly is viewed.—F.V.T.]
(Wohlfahrt: “Observ. de vermibus per nares excretis,” HalÆ, 1768; Nov. Act. Acad. Caes. Nat. curios., 1770, iv, p.277. GerstÄcker in: Sitzungsb. Ges. nat. Frde. Berl., 1875, p.108. Portschinsky in: HorÆ soc. entom. ross., 1875, 1884, p.123. LaboulbÈne in: Ann. Soc. ent. France, 1883 (6), iii; Bull., p. xcii. Leon in: Bull. Soc. des MÉd. et Nat. de Jassy, 1905, xix, p. i. Freund, L., in: Verh. Ges. deutsch. Naturf. u. Ärzte, Homburg (1902), 1902, ii, 2, p.450, and other authors.) [Probably most cases of attack in Europe are due to this species.—F.V.T.]
The above cited do not exhaust the number of observations of diptera larvÆ parasitic in man; there are yet to be mentioned the larvÆ of S. hÆmorrhoidalis, S. hÆmatodes (of G. Joseph), those of S. ruficornis (excitants of a cutaneous myiasis in the East Indies), those of species of Eristalis (of Hanby and others), and those of Phora rufipes (of Kahl, of Warsaw, and others). In many cases the determination of the diptera larvÆ has been omitted (or must be omitted); such is the case with diptera larvÆ in the eye (Schultz-Zehden in: Berl. klin. Wochenschr., 1906, p.286. Ollendorf in: Med. Korrespondenzbl. d. wÜrt. Ärtzl. Landesver., 1904, p.1017. Kayser in: Klin. Monatsbl. f. Augenheilkunde, 1905, xliii, i, p.205. Ewetzky and v. Kennel in: Zeitschr. f. Augenheilkunde, 1904, xii, p.337, and other cases). Austen
The larvÆ of African MuscidÆ have now become of greater interest; like several Oestrid larvÆ they live normally in the skin of mammals, but also attack man. The knowledge of these species is certainly very insufficient, but this is not likely to be the case much longer, as medical men practising in the Colonies are giving their attention to these parasites. At the present time four distinct forms are recognized according to Gedoelst.413
Sarcophaga chrysotoma, Wied.
[This species is recorded as attacking human beings at New Amsterdam, British Guiana. The fly is 15mm. long, has a golden-coloured face, three broad black thoracic stripes and ochraceous buff anal segments. It was bred from larvÆ obtained by Dr. Roland from a sore on a girl’s foot. It is known to occur in the Brazils and the West Indies. Another species was also bred which Austen was unable to identify.—F.V.T.]
Sarcophaga plinthopyga, Wied.
[This and other species of Sarcophaga are called “yaw flies” in Dominica, as they are believed to be concerned in the dissemination of framboesia or yaws (Nicholls) (vide Austen, Trans. Soc. Trop. Med. and Hyg., 1910, iii, p.239).—F.V.T.]
Fig. 409.—Ochromyia larva on the skin of man, South Africa. 3/1. (After Blanchard.)
Ochromyia anthropophaga, E. Blanch.; Cordylobia arthrophaga, GrÜnberg.
Indigenous to the Senegal and neighbouring districts; in the district of Cayor (between the mouth of the Senegal and Cape Verde) the larva is known as the “ver de Cayor.” It lives under the skin, especially at the lower extremities and the lower region of the trunk, producing small boils, which cause pain, but after about eight days, when the larva leaves the body to enter the pupal stage, the pain discontinues. Besides man the larva occurs in dogs, goats, cats, and in the jackal. It is still questionable whether the fly deposits its eggs direct or on the ground, from whence the larvÆ as they emerge gain access to animals and man. LarvÆ yellowish-white, 14mm. long, 4mm. wide, eleven segments414; head with two globular antennÆ-like appendages, two black curved mouth hooks, and two wart-shaped, finely spinous structures at their base. Body evenly covered to the seventh segment with small black prickles, which are stronger at the sides and the anterior borders of the segments; from the seventh they increase in size, on the two hindermost they are wanting; on the last segment two deep yellow spiracles, each with three markedly curved fissures; in
Auchmeromyia (Bengalia) depressa (Walker).415
Fig. 410.—Head end of “larva of Natal.” Magnified. (After Gedoelst.)
Distributed in the region of Natal and apparently over the whole of South Africa. The “larva of Natal,” as one may still term the species provisionally, as its identity is not certain, possesses on its head (besides the mouth hooks) lateral protuberances beset with a row of chitinous spines. The cuticle of the body is spinose. The spines are difficult to recognize on account of their transparency and want of colour; they are longest over the anterior segments, from the fifth they become smaller, and over the hindermost they are very small. Apart from the foremost segment, the position they take is that of rows running transversely or obliquely, two to four generally in juxtaposition; the number of spines in the groups gradually increases posteriorly, attaining the number of eight to twelve on the sixth segment, and this number is maintained to the end of the body. Isolated spines are found over the head; over the second, third and fourth segments single ones are still found adjoining the groups of spines, from the fifth onward they are wanting. From here the spines cover the whole free surface of the segments; over the fourth the anterior three-quarters, over the third two-thirds and over the first and second only the anterior half. The stigmata found at the anterior end also serve as distinguishing characters. The parasitic stage appears to last about fourteen days. [Fuller (Agric. Journ., Dept. Agric. and Mines, Natal, 1901, iv, p.606) refers to this as Bengalia depressa also.—F.V.T.]
Genus. Cordylobia, GrÜnberg, 1903.
Cordylobia grÜnbergi, DÖnitz.
Syn.: Ochromyia anthropophaga, GrÜnberg, nec Blanch.; Cordylobia anthropophaga, GrÜnberg.
Endemic in German East Africa and neighbouring regions. Larva up to 14mm. long, 4 to 5·5mm. wide, of cylindrical shape, slightly narrowed behind, truncated, gradually tapering in front; antennÆ-like processes, cone-shaped, blunt.
Cordylobia anthropophaga, GrÜnberg.
This well-known cutaneous African parasite seems to have been the cause of much confusion in regard to names. It belongs to the genus Cordylobia of GrÜnberg, and is one of the family MuscidÆ, and differs from Auchmeromyia in that the second abdominal segment of the female is of normal size, whilst in Auchmeromyia it is more than half the length of the whole abdomen, and in the male the eyes are holoptic or close together, whilst in Auchmeromyia they are wide apart. The flies of this genus (three so far described) attack man in their larval stage (anyway two of the three), and also dogs and other animals, by burrowing into the skin and producing painful boils.
[C. anthropophaga, GrÜnberg, is widely distributed in Africa, extending from Senegal, where its maggot is known as the “ver de Cayor,” and is referred to on p.590 as Ochromyia anthropophaga, E. Blanchard, to Natal, where it is known as the “Natal worm,” and referred to erroneously on p.591 as Bengalia depressa, Walker.
[It is a thick-set Muscid of a general straw-yellow colour, with blackish markings on the dorsum of both thorax and abdomen, about 9·5mm. long. The larva is fat and when mature about 12mm. long, bluntly pointed in front, truncate behind; from the third to eleventh segments it is thickly covered with minute recurved spines of a brownish colour, arranged in transverse series of groups of two or more, which form more or less distinct irregular transverse rows. On each of the two posterior stigmatic plates, the respiratory slit on either side of the median one is characteristically curved, resembling an inverted note of interrogation. The puparium is brown to ferruginous or black and about 10mm. long. The maggots are found in both natives and white men, and occur as a severe pest in dogs, also in monkeys, rats, and other mammals. In Sierra Leone it is called the “tumba fly.” The larvÆ have been frequently found as true subcutaneous parasites, each larva living singly and forming a boil or warble in the skin, with an opening just as in an ox-warble, through which the maggot breathes and eventually escapes. Although they more usually occur as isolated specimens, Marshall found in Salisbury, South Rhodesia, that sixty were extracted from one lady, and BÉrenger-FÉraud, in Senegal, that more than 300 occurred in a single spaniel puppy.
[Neave (Bull. Ent. Res., 1912, iii, p.217) records it from ulcers in a native at LourenÇo Marques in 1908, and at the same time from ulcers in a dog, and that it is a severe pest to man in Mozambique and parts of the Transvaal. It seems to be more abundant in North Rhodesia and Nyasaland than to the north (Neave, Bull. Ent. Res., 1912, iii, p.310). It is also recorded in Zanzibar, German East Africa, Uganda, East Tropical Africa (Neave).
[Simpson (Bull. Ent. Res., iii, p.170) records a Muscid larva taken from the breast of a European in South Nigeria that was probably Cordylobia.
[It is not known how infection takes place. Neave (Bull. Ent. Res., iii, p.310) says:
[Gedoelst has described another species, C. rodhani, and Austen a third species, C. prÆgrandis, from Nyasaland, Cape Colony, Transvaal, Natal, North-west Rhodesia, and German East Africa.
[The following are some papers dealing with this subject: Proc. Ent. Soc., London, for year 1907, p. xlvii; Journ. R.A.M.C., 1908, pp.5–11, figs.1 and 2, by Austen; Journ. R.A.M.C., 1908, pp.1 and 2, by Major F. Smith; Trans. Soc. Trop. Med. and Hyg., 1910, iii, pp.223–225, by Austen.—F.V.T.]
Lund’s Larva.
Fig. 411.—Lund’s larva: on the left, the whole larva, magnified six times. On the right, the head end, much enlarged. (After Gedoelst.)
Endemic in the region of the Congo State; called after Commander Lund, from the skin of whose arm it was extracted; 12·5mm. long, 4·5mm. broad; colour yellowish, with brown rings, on account of the division of the brown spines; head cone-shaped, with two hemispherical smooth antennÆ, two thick black mouth hooks and wart-shaped bodies, between which are situate two to three longitudinal rows of dark brown chitinous laminÆ. The body segments are covered over their whole surface with irregularly distributed triangular yellow spines, the points of which are coloured dark brown. Its size increases from the second to the sixth segment, diminishes from the seventh to the ninth, at the tenth it is reduced, and at the eleventh quite small. The posterior stigmata are bean-shaped, each with three markedly tortuous openings. Duration of the larval stage unknown; the same applies to the pupal and imago stages.
Auchmeromyia luteola, Fabricius.
[This fly, the parent of the so-called Congo floor maggot,416 belongs to a nearly allied Muscid genus to Cordylobia, but which can at once be told by the great length of the second abdominal segment. The maggot occurs in numbers in the
Family. OestridÆ.
[The family of OestridÆ or warble flies are all parasitic in their larval stage, usually termed the “bot” stage. They are found as parasites in warm-blooded animals, and man is frequently attacked by them. The members of this family have the mouth rudimentary, many of them are hairy and bee-like, with large eyes and the head large, the lower part more or less swollen. The thorax is large with a distinct transverse suture, and the abdomen short and stumpy or very slightly elongated. The male genitalia are hidden, whilst the female ovipositor is often elongated. The wings may be transparent (Hypoderma) or mottled (Gastrophilus), and have muscid-like venation; the tegulÆ usually large, the legs moderately long.
[As a rule each species is confined to a particular host, but as we see recorded here those that attack animals may also attack man. The flies occur in warm weather and usually during the warmest part of the day, and have a strong dislike to shade and water. The genus Hypoderma attack oxen, sheep, goats, antelope and musk deer; Oestrus, sheep, antelope and horses; Gastrophilus, the horse and ass; Cephenomyia, the deer; Cepholomyia, the camel and buffalo; Dermatobia, dogs, cats, oxen, deer, apes and man; Cuterebra and Rogenhofera, rodents and opossums.
[Some live as parasites in the stomach and intestines (Gastrophilus); others infest the skin (Hypoderma, Dermatobia and Oestromyia, the latter on Lagomys and HypodÆus); Œdemagena tarandi also infests the skin of the reindeer in Siberia and boreal America. Oestrus lives in the nasal sinus, and Cephalomyia in the throat as well, Cuterebra and Rogenhofera, the skin or scrotum, so that we have really three groups of parasitic oestride larvÆ: (i) cutaneous, (ii) intestinal, and (iii) facial.
[No species seems confined to man, but the so-called “creeping disease,” caused by HypodermÆ, and the attack of sheep nasal fly are comparatively common, as also is the Dermatobia attack.—F.V.T.].
Cutaneous OestridÆ.
The eggs are deposited on the surface of the body; the larvÆ burrow in the skin, which they reach after somewhat long peregrination.
Genus. Hypoderma, Latreille.
Hypoderma bovis, de Geer.
The cattle fly or warble fly, which swarms during the hot season, settles on the head or on the hair of grazing cattle: through the young being licked off they gain access to the mouth and are swallowed.419 The larvÆ appear first in the commencing portion of the stomach, to escape, as some state, into the preceding sections of the alimentary canal; at any rate, they are found from July onward regularly in the submucous tissue of the pharynx, in which they travel about for several months (up to November, and in isolated cases up to February); they then penetrate the muscularis and migrate by way of the subserosa along the mediastinum, the crura of the diaphragm, the renal capsules, and the intermuscular connective tissue of the psoas muscle in the direction of the spinal canal, into which they penetrate by way of the muscles and nerves, through the intervertebral foramina. Here they stay for about two to three months, then they leave the spinal canal again through the vertebral foramina and make their way (from January to March) through the intermuscular connective tissue of the muscles of the back to the skin of the back, where sooner or later (from January to June) they arrive and enter a resting stage, which commences with penetration of the skin and terminates with outward migration from the boils due to the wound set up by the maggot. At the commencement of this period the larvÆ cast their skin, and their form, hitherto cylindrical, becomes oval. After about a month, a second moulting of the skin takes place—the third larval stage, which lasts about two and a half months (up to June). The approaching end of the same is indicated by a change of colour on the part of the larva from the hitherto yellowish-white to brown and finally to blackish-brown. When they have become mature the larvÆ leave the warbles, drop on to the ground and pass into the pupal stage in the superficial layers of the soil within twelve to thirty-six hours. After about a month the flies emerge. Irregularities with regard to the time and direction of the migrations of the larvÆ take place (Jost, H., in Zeitschr. f. wiss. Zool., 1907, xxxvi, p.644).
In a number of cases the larva of the cattle fly has been observed in the human integument, usually in the winter months, that is, during the migration period; consequently, it is not surprising that the larvÆ before they enter on the resting stage and produce a warble undergo migrations. But that this takes place subcutaneously—which does not appear to be so in the case of cattle—is perhaps explained by the fact that in man, on account of the short space that has to be traversed, the larvÆ are not sufficiently developed to enter on the resting stage simultaneously upon having obtained access to the integument. Whether the Oestrid larvÆ in Bulgaria that similarly migrate beneath the skin in man belong to the cattle fly or to another species, or even another genus, has not yet been
Hypoderma lineata, de Villers.
The larvÆ of this species, that occurs not only in Europe but in North America, live under similar conditions in the skin, very rarely in man; also migrating subcutaneously (Topsent in Arch. de Par., 1901, iv, p.609).
[In Sweden, the ox warble fly (H. bovis) is well known to attack man. Schoyen states “that over 100 years ago up to the present time cases of travelling grubs under the human skin in some districts of Sweden were well known.” The species appeared to be H. bovis, many of which he had examined. They accomplished long ramblings under the skin, always in an upward direction, previous to their appearance through an opening in a tumour on the upper part of the body, on the head, neck, or shoulders. An interesting case is recorded in Insect Life, ii, pp.238–239. A bot similar to H. diana was taken from the eye and cheek of a child at Kane, McKean County, Pa., U.S.A. It was said to have travelled in five months from the elbow to the eye. Riley later (Insect Life, iv, p.310) was inclined to think the maggot was that of H. lineata, the common American ox warble, which is also found in Europe in great numbers. I have recorded another case in England (Rept. Econ. Zool. for year ending September 30, 1910, p.128), where Dr. Menzies removed the larva of H. bovis from the upper eyelid of a patient. It caused considerable swelling of the face, much pain and distress; but the case did well, and the wound healed at once. The larva was nearly mature. Numerous other references to this so-called creeping disease will be found in the Supplement.
[It is quite probable that bovis and lineata are confused in the latter accounts. The larvÆ are, however, easily distinguished if carefully examined.—F.V.T.]
Hypoderma diana, Brauer.
In its larval stage it lives like other species of Hypoderma, attacking the red deer (Cervas elaphas) and roe deer (Cervas capreolus); it is occasionally also found in man (Joseph, in “Myiasis externa dermatosa,” Hamburg, 1800; VÖlkel, in Berl. klin. Wochenschr., 1883, xx, p.209).
Genus. Dermatobia, Brauer.
Dermatobia cyaniventris, Macq.
Syn.: Dermatobia noxialis, J. Goudot.
The genus Dermatobia represents the subcutaneous OestridÆ of Europe in warmer parts of America. Both domesticated and wild mammals are attacked, according to one statement birds also (Ramphastus), and man with fair frequency.420 It is assumed that in all cases one and the same species is concerned, for which recently a name originating from C. LinnÉ, jun. (Oestrus hominis), has been employed. Three larval stages are recognized in the skin; the two first appear to
Fig. 412.—Dermatobia noxialis, Goudot.
Fig. 413.—Larva of Dermatobia cyaniventris in its natural size and magnified. (After Blanchard.)
Fig. 414.—Larva of Dermatobia cyaniventris. Enlarged. (After Blanchard.)
[Dermatobia cyaniventris, Macquart, 1843, is said not to be the same as noxialis (vide Brauer, “Mono. Oestriden,” 1863, p.266). It is known by various other names,
[It is seldom that more than one larva is found in each individual. It is generally found in the arm and leg, but now and then the face. The perfect insect has never been bred from a larva removed from a human being, so that there is still uncertainty as to the actual species. D. cyaniventris is 11 to 12mm. long, has an ochraceous buff-coloured face, dark grey thorax, metallic dark blue to purple abdomen, and brownish wings. D. noxialis is somewhat larger.
[In the Journal of Tropical Medicine and Hygiene, January 15, 1905, viii, p.23, reference is made to this Oestrid in Trinidad, where it is called the “mosquito worm.” One case here recorded showed no fewer than four worms on the chin and one on the hand. It is here stated that the fly never attacks man or animals directly, as it is said to do by Scheube, but that the eggs are deposited on leaves and branches in wooded lands and forests, and thus man, hunting dogs and wild animals in passing through get the larvÆ deposited on them accidentally. The affection is common in Trinidad. Mention is made that a little 1 in 40 carbolic lotion syringed into the aperture in the skin over the worm quickly killed it.
[The cattle worm, or founzaia ngÓmbe, is the name given to a larva which develops beneath the skin of oxen and men in Central Africa, especially amongst the natives and stock of Unyamonezi. According to P. Dutrieux, the egg is laid by a large fly that accompanies cattle. It is unknown between the central plateau or the Ugogo and the East Coast.—F.V.T.]
Cavicolous OestridÆ.
The forms belonging to this group inhabit as larvÆ the nasal and frontal sinuses of ruminants, EquidÆ and ProboscidÆ, which they leave for the pupal stage. The larva of—
Genus. Oestrus, LinnÆus,
Oestrus (Cephalomyia) ovis, L.,
occurring in sheep, has also been observed in man in six cases in the nose and larynx (Saitta in Gaz. d. Osp. d. Clinic, 1903, No. 128). So far as is known, the eggs are deposited in the nasal cavity.
[Oestrus ovis frequently occurs in man. MM. Sergent (Ann. de l’Inst. Pasteur, 1907, pp.392–399) mention that they lay their ova on the noses, eyes and mouth of humans in Algeria whilst flying, but that they disappear after three to ten days or the inflammation produced by them. Portschinsky (Mem. Bur. Ent. Sci. Com. Cent. Bd. Land Adm. and Agric., 1913, x, No. 3, p.63) also gives cases. He doubts that ova are laid on the nose; evidently the Russian habit is anomalous, for the Sergents, Collings and myself find ova laid as a common occurrence. I have often seen them on the nose of sheep. This fly also occurs in the Argentine (Serres, in Gaceta Rural, April, 1913, vi, pp.759–761).
[The tamnÉ or thimni of the Kabyles, a human myiasis of the Tuareg mountains in the Sahara, is caused by Oestrus ovis. Here the larvÆ are said to be ejected on to the conjunctival and nasal mucous membrane of humans.
[Ed. and Lt. Sergent (Bull. Soc. Path. exot., 1913, vi, No. 7, pp.487–488) report their attack from the Ahaggar mountains, in Central Sahara. The Tuareg name for the fly, tamnÉ, is the Targui form of the word thimni used by the Kabyles.—F.V.T.]
Gastricolous OestridÆ.
The eggs are deposited on the hairs of EquidÆ, and the larvÆ escaping from them are licked up and swallowed. They pass their larval stage, according to the species, in various parts of the intestine and stomach, and when mature, pass out per anum in order to undergo the pupal stage.
Genus. Gastrophilus, Leach.
One of the most frequent species is Gastrophilus equi, Fabr.; the eggs are laid on the hairs; the larvÆ live some ten months in the stomach, living attached to the inner surface. The eggs of G. hÆmorrhoidalis, L., are deposited on the lips or the long hairs on them. The larvÆ adhere to the cardiac end of the stomach, to the stomach itself, and finally to the terminal portion of the intestine. Here, however, and elsewhere in the intestine, the larvÆ of G. pecorum, Fabr., are also met with, whilst the larvÆ of G. nasalis (so called because the eggs are deposited in the nasal orifices) almost exclusively inhabit the anterior section of the duodenum.
Cholodkowsky attributes the “wormlet” observed by Samson and Sokolew (Wratsch, 1895, Nos. 48 and 57) and others (ibid., 1896–98) to Gastrophilus larvÆ. It burrows into the epidermis of man by minute passages. This observation should, however, be verified. The phenomenon is designated as skin-mole, larva migrans, and creeping eruption.
Other Papers on Dipterous LarvÆ, etc., in Man.
(1) “Ein Fall von lebenden Fliegenlarven im menschlichen Magen,” Deutsch med. Wochenschr., Leipz. and Berl., xxiv (12), pp.193–194. Bachmann, and review of same, “Living Fly LarvÆ in the Human Stomach,” Philadelphia Med. Journ., 1898, i, 18, p.773.
(2) “Sudi una larva di dittero parassita della congiuntiva umana,” Ann. di ottal., Paira, 1895, xxiv (4), pp.329–336, 1 fig., E. Baquis.
(3) “Sur quelques diptÈres suceurs de sang, observÉ À Terre-Neuve,” Arch. de Par., Paris, 1900, iii (1), pp.202–204, E. Barret.
(4) “An Account of the LarvÆ of two Species of Insects discharged from the Human Body,” Edin. Med. and Surg. Journ., January 1, 1811, vii (25), pp.41–48, 1 pl., figs.1 to 8, T. Bateman.
(5) “Un cas de myiase par la Sarcophaga magnifica en Roumanie,” Bull. Soc. Zool. de France, Par., 1891, xvi (2), pp.25–26, R. Blanchard.
(6) “Sur les oestrides amÉricains dont la larve vit dans la peau de l’homme,” Ann. Soc. ent. de France, 1892, v, pp.109–154, figs.1–12, R. Blanchard.
(7) “Note additionnelle sur les oestrides amÉricans dont la larve vit dans la peau de l’homme,” Bull. Soc. ent. de France, Paris, 1894, xiv, pp.209–211, R. Blanchard.
(8) “Note sur des larves de Dermatobia provenant de BrÉsil,” Bull. Soc. ent. de France, Paris, 1893 (2), pp.24–27, R. Blanchard.
(9) “Larven der Wohlfahrtfliege (Sarcophila wolfahrtii) im Zahnfleische eines Menchen,” Wratsch., St. Petersburg, 1888, 5–6, E.K. Brandt.
(10) “Ueber den sogenannten Oestrus hominis und die oftmals besichteten Verirrungen von Oestriden der SÄugetheiere zum Menchen,” Verhandl. d. k. zool.-bot. Gesellsch., 1860, x Abhandl., pp.57–72, Brauer.
(11) “Ueber die Larven der Gattung Cuterebra, Clk.,” Verhandl. d. k. zool.-bot. Gesellsch., 1860, x Abhand., pp.777–786, Brauer.
(12) “Des dÉsordres produits chez l’homme par les larves de la Lucilia hominivorax,” ThÈse, Paris, 1864, 43 pp., V. Audouit.
(13) “Note on the ‘Flesh Worm,’ ” Med. Press and Circ., London, April 12, 1882, lxxxii (N.S. xxxiii), p.314, P.S. Abraham.
(14) “Larvas de la Calliphora limensis en fosas nasalis,” 1855, 18 pp., F. Aguirre.
(15) “Raro caso di parasitismo nell ’uomo dovuto alla larva di una mosca (Sarcophaga affinis, Meigen),” Boll. d. Soc. Rom. per gli Stud. Zool., Roma, 1893, iv (5–6), pp.278–289, 1 pl., 3 figs., Giulo Alessandrini.
(16) “Observations sur l’espÈce de ver nommÉ Macaque (Oestrus),” MÉm. Acad. Sci. par Hist., 1753, p.72, F. Artur.
(17) “ContribuiÇÃo ao estudo da biologia da Dermatobia cyaniventris,” Trav. do Inst. de Manguinhos, 1908.
Biting-mouthed and other Noxious Diptera which may be Disease Carriers.
[Amongst the division Brachycera (as meant in this work) we get several groups of flies which, like the fleas and mosquitoes, are partially parasitic on man, the adults, mainly in the female sex, being provided with a piercing mouth with which they extract the blood of man and animals. The importance of these parasites is not the mere fact that they feed upon our blood, but that they often carry germs from man to man (tsetse-flies and trypanosomiasis, TabanidÆ and anthrax). Amongst the most important biting-mouthed Diptera in this section are the following: TabanidÆ, or gad-flies; GlossinÆ, or tsetse-flies; and certain other MuscidÆ. Some of the exotic AsilidÆ and a few LeptidÆ also bite man.
Family. TabanidÆ (Gad-flies).
[The TabanidÆ have a broad, rather flattened body and a large head; eyes united in the male (except in some Chrysops). The antennÆ are composed of three segments, have the third joint composed of five to eight annuli—in Chrysops they are fairly long. The proboscis is projecting, and sometimes much elongated. The legs are moderately stout. The venation of the wings is shown in fig.415.
[This family of gad or horse flies contains a great number of genera, all of which may bite animals and man more or less severely. The female alone is blood-sucking, the males feed upon the juices of flowers. The females deposit their spindle-shaped white, black, or brown eggs on leaves, stems of plants that either overhang or stand in water, and amongst rushes; they are at first white, but become brown or black. The eggs are laid in rounded, flattened or conical masses composed of layers one upon the other. The larvÆ are carnivorous, feeding upon snails, worms, other larvÆ, etc., and have a distinct head; they are cylindrical, composed of eleven segments, the last with a vertical breathing pore, or the last two segments may form a breathing tube. The majority taper to a point at each end, in colour shining white or dull grey to yellowish, many of the larger specimens mottled or banded with dark brown or black. The first seven abdominal segments are encircled near the anterior margin with a ring of fleshy protuberances consisting of a transverse dorsal ridge which may be divided by a depression into two. The young larvÆ burrow into any soft vegetable substance; they live both in the water and under damp soil surrounding water, also in damp earth generally. The larvÆ are not only carnivorous, but they are cannibals, frequently devouring their own species. They may take more than a year to mature.
[The pupÆ are found close to the surface of mud and earth, and are mostly dull yellowish to brown in colour, with rows of spines on the distal third of each abdominal segment; the thorax bears a pair of ear-shaped spiracular structures, and there are also six denticles at the apex of the abdomen.
[A habit common to the adults of most of the TabanidÆ of considerable economic
[TabanidÆ are not only of importance as purely biting insects, for they may often convey pathogenic organisms from one animal to another, such as the bacillus of anthrax, which they are known to carry, and possibly also trypanosomes in regard to man. Chrysops also acts as a host of Filaria loa in South Nigeria (Leiper, Brit. Med. Journ., January, 1912, pp.39–40). Two species are incriminated, viz., C. silacea and C. dimidiata. With animals these flies play a more important part, for MM. Sergent, in Algeria, have proved that species of Tabanus are able to transmit three forms of animal trypanosomes by biting a healthy animal as long as twenty-two hours after having bitten an unhealthy one. In India they have also been shown to transmit the parasite of “surra” in dogs and rabbits by Rogers. Other observers have since corroborated these results, and Mitzmain, who has recently performed valuable work in this connection, states that T. striatus is undoubtedly the carrier of this disease in the Philippine Islands. Certain members of the genus HÆmatopota have also been shown to be capable of the direct transmission of Trypanosoma evansi. Martoglio (Ann. d’Ig. sper., 1913, xxiii, N.S., No. 3, pp.363–366) states that the trypanosome disease of dromedaries known as salaf is transmitted by TabanidÆ, especially Pangonia (P. magretti and P. beckeri) in Italian Somaliland. It is quite likely that these flies play a much greater part in the spread of such diseases than is imagined at the present time.
Fig. 415.—The ox gad fly (Tabanus bovinus, Linn.).
[The TabanidÆ are divided into two groups or subfamilies: (1) The PangoninÆ, and (2) the TabaninÆ; the former have spurs on the hind tibiÆ and usually ocelli; the latter have neither tibial spurs nor ocelli.
[The PangoninÆ contain two main genera, Pangonia and Chrysops. In the former the proboscis is much elongated, and the third antennal segment is composed of eight rings, and is never angulated or ungulated at the base. The proboscis is often very long.
[In Chrysops, the so-called blinding storm flies, all the three segments of the antennÆ are long, the third having only five annulations, and the proboscis short but very strong.
[There are many genera in the TabaninÆ, which are found in all parts of the world, of which two only are shown here—viz., Tabanus and HÆmatopota. The former has the first two segments of the antennÆ short, the third angulated at the base, sometimes spurred and composed of five annulations; the second has the second segment short, and the third composed of four annulations—never angulated nor spurred at the base—and the wings are adorned with grey or brown markings. These latter are usually called “brimps” and “clegs” in Britain, the former gad or horse flies, the seruts and mangrove flies of tropical countries.
Fig. 416.—The brimp (HÆmatopota pluvialis, Linn.).
Family. AsilidÆ (Wolf Flies).
[These flies are of little importance in regard to the subject dealt with in this book; but I have notes sent concerning the biting habits of one or more species belonging to this family from the Malay States and Africa.
[AsilidÆ, or wolf flies, are easily told by the following characters: Large or moderate-sized flies, thickly hairy; head separated from thorax by a narrow neck; eyes separated in both sexes; proboscis firm and horny, adapted for piercing; abdomen long, pointed, and composed of eight segments. Legs strong and bristly, of moderate length. Wings sometimes mottled, lying parallel over the abdomen when at rest. There are nearly 3,000 species. They live mostly upon insects, but some are said to bite animals and man. They are, however, of little importance in this respect.
Family. LeptidÆ.
[This widely distributed family of flies has a few species which suck the blood of man, and the writer has been personally badly bitten in Norway by a Leptis which was apparently Leptis scolopacea.
[The LeptidÆ have usually blotched wings and similar venation to Tabanus; they are elongated flies of moderate or large size, and of dull colours. The antennÆ are varied and consist of three segments, either with or without a terminal bristle or with the third segment compound, and in a few they may be almost nematocerous. The wing veins are distinct, very crowded anteriorly, the third long vein is furcate, basal cells large, and there are usually five posterior cells, the anal cell being open in some; the squamÆ are always small, sometimes only rudimentary.
[Four are known to be blood-suckers, namely the American Symphoromyia, Trichopalpus obscurus in Chili, and Leptis strigosa and L. scolopacea in Europe. The genus Symphoromyia has a single spur on the hind tibiÆ, none on the fore or mid tibiÆ, the third segment of the three-ringed antennÆ kidney-shaped, and a short proboscis. In the genus Leptis the hind tibiÆ have two spurs, and the third antennal segment is not reniform.
[The other biting genus Trichopalpus can be told at once by the elongated proboscis. Most of this family live upon other insects. The larvÆ live in earth, decaying wood, sand, stagnant waters, and the nests of wood-boring beetles; they are usually cylindrical and may have fleshy abdominal legs; the anal segment has a transverse cleft, and often two posteriorly directed processes and two stigmata between them. They are all predaceous, and in one genus (Vermileo) make pitfalls in sand like the ant lions (Myrmeleon).
Blood-sucking MuscidÆ.
[The blood-sucking MuscidÆ are mainly contained in the following genera: Glossina, Stomoxys, HÆmatobia, Lyperosia, Stygeromyia, PhilÆmatomyia and Bdellolarynx.
[The first is the most important genus on account of the part it plays in the spread of trypanosome diseases. Stomoxys may also serve as a disease carrier. The remainder and a few more genera cause considerable annoyance by their bites, and may also act as occasional carriers of pathogenic organisms. All these flies have their mouth parts elongated to some extent, forming a distinct proboscis, which becomes more or less strongly chitinized; the labella are usually serrated or spiny, and thus form a structure easily capable of piercing the skin. Unlike the CulicidÆ, the blood-sucking MuscidÆ have the sanguinary habit common to both sexes.
Genus. Glossina, Westwood.
Fig. 417.—Head of Glossina longipalpis, Wied. (After GrÜnberg.)
[This genus contains sixteen species,423 all of which are confined to the Ethiopian region. Glossina may be distinguished from other allied genera by the proboscis, the antennÆ, wings, and male genitalia. The proboscis projects forwards and has a swollen bulb-like base to the slender labium which holds the two structures, the needle-like epipharynx and the thread-like hypopharynx; the whole proboscis is
[Newstead has shown the importance of the study of the genitalia in separating species (vide Bull. Ent. Res., ii, pp.9–36 and 107–110, and iii, pp.355–360; and Ann. Trop. Med. and Par., vii, No. 2, pp. 331–334).
Fig. 418.—Antenna of Glossina pallidipes, male. (After Austen.)
[The tsetse-flies reproduce differently from all other MuscidÆ. The female produces at each birth a single full-grown larva, which is retained within the oviduct and there nourished by the secretion of special glands, and on being born crawls to some hiding place and at once becomes a puparium.
[The larva is a yellowish footless maggot nearly as large as the mother’s body, the skin shagreened and the anal extremity having a pair of large, black, granular prominences separated by a depression containing the breathing pores.
[The puparium is brown of various shades, the tumid lips of the larva being conspicuous, the size and shape of the lips enabling the puparia to be identified.
[These puparia are often found in masses at the base of trees, in hollows in trees and rocks just buried under vegetal debris. These insects are generally confined to definite tracts known as “fly-belts.” They usually occur in damp, hot places on the borders of rivers and lakes, and never far from water in the case of the palpalis group, although others of the morsitans group may be found a considerable distance from water. They are usually absent on grass plains, but may now and then occur there (Kinghorn, vide Hindles’ “Flies and Disease, Blood-sucking Flies,” 1914, p. 274); cover of trees, shrubs, or thick reeds is essential to them.
[Their range in Africa extends roughly from 18° N. to 31° S.
[Glossina palpalis is the chief carrier of the more prevalent type of sleeping sickness. Two distinct types of parasites can produce this disease, viz., Trypanosoma gambiense, which produces the ordinary sleeping sickness, transmitted by G. palpalis, and Trypanosoma rhodesiense the Rhodesian or Nyasaland sleeping sickness, transmitted by G. morsitans, and possibly identical with T. brucei, the parasite of N’agana. Koch has also shown that G. pallidipes, Austen, and G. fusca, Walker, can be artificially infected with the human trypanosome. It appears probable that Koch used G. brevipalpis, not G. fusca, in his transmission experiments, as at that time fusca included nearly all the large tsetses, but brevipalpis is its Eastern representative.
[A Table of Species (modified after Austen) is appended here:—
| I. | ||
| Glossina palpalis Group. | ||
| 1. | Dorsum of abdomen ochraceous buff or buff; third and following segments exhibiting sharply defined, dark brown or clove brown, interrupted transverse bands | tachinoides, Westwood. |
| Dorsum of abdomen not so marked | 2. | |
| 2. | Third joint of antennÆ pale (cream buff to ochraceous buff), clothed with long and fine hair, forming a conspicuous fringe on front and hind margins | pallicera, Bigot. |
| Third joint of antennÆ entirely dark (mouse-grey) except at extreme base on outer side, and without a conspicuous fringe of long and fine hair | 3. | |
| 3. | Dorsal surface of abdomen dark sepia brown; median paler area on second segment broad, and more or less quadrate or irregular in outline; hypopygium of ? buff or ochraceous buff | caliginea, Austen. |
| Dorsal surface of abdomen blackish-brown; median paler area cuneate (i.e., triangular in outline); hypopygium of ? grey | palpalis, Rob. Desv. | |
| II. | ||
| Glossina morsitans Group. | ||
| 1. | Hind tarsi entirely dark; small slender species; abdomen bright ochreous or reddish ochreous with dark lateral markings | austenii, Newstead. |
| Hind tarsi not entirely dark; abdomen drab-grey, buff or ochreous buff with conspicuous dark interrupted transverse bands | 2. | |
| 2. | Last two joints of front and middle tarsi with sharply defined clove brown or black tips | 3. |
| Last two joints of front and middle tarsi without sharply defined clove brown or black tips (front and middle tarsi either entirely pale or, at most, two joints of front tarsi faintly brownish at the tips), and last joint and distal half of penultimate joint of middle tarsi light brown, never so dark as to form a sharp contrast with the remaining joints | pallidipes, Austen. | |
| 3. | Third joint of antennÆ with a distinct fringe of fine hair on front margin; dark brown or clove-brown bands on abdominal segments extending close to hind margins (i.e., pale ground colour, apart from the median interspace, confined to a very narrow hind border) | longipalpis, Wiedeman. |
| Third joint of antennÆ without a distinct fringe of fine hair on front margin; dark brown or clove-brown bands on abdominal segments not extending close to hind margins | morsitans, Westwood. | |
| III. | ||
| Glossina fusca Group. | ||
| 1. | Third joint of antennÆ fringed with fine hair on anterior and posterior margins; fringe on anterior margin conspicuous under a hand lens magnifying 15 diameters (nominal) when head is viewed in profile | 2. |
| Third joint of antennÆ with fringe of fine hair on anterior margin so short as to be scarcely noticeable under a hand lens magnifying 15 diameters (nominal) when head is viewed in profile (longest hairs in fringe in length not exceeding one-sixth of width of third joint); palpi long and slender | 3. | |
| 2. | Longest hairs in fringe on front margin of third joint of antennÆ, in length equal to from one-fourth to one-third (not exceeding one-third) of width of third joint; palpi of moderate length | tabaniformis, Westwood. |
| Longest hairs in fringe on front margin of third joint of antennÆ in length equal to from one-half to three-fourths of width of third joint; palpi noticeably long and slender | nigrofusca, Newstead. | |
| 3. | PleurÆ drab-grey or isabella-coloured, hind coxÆ buff or greyish-buff | fusca, Walker. |
| PleurÆ dark grey; hind coxÆ mouse-grey | fuscipleuris, Austen. | |
| IV. | ||
| Glossina brevipalpis Group. | ||
| 1. | Dorsum of thorax with four sharply defined brown, more or less oval or elongate spots, arranged in a parallelogram, two in front and two behind the | longipennis, Corti. |
| Dorsum of thorax without such spots; proboscis bulb not brown or dark brown at tip | 2. | |
| Wings with upper thickened portion of anterior transverse vein much darker in colour than adjacent veins and thus standing out conspicuously against the rest of the wing | brevipalpis, Newstead. | |
| Wings with upper, thickened portion of anterior transverse vein not much darker in colour than adjacent veins, and thus not standing out conspicuously against the rest of the wings (wings practically unicolorous) | medicorum, Austen.424 | |
Glossina palpalis, Rob. Desv.
Fig. 419.—Glossina palpalis and puparium. (After Brumpt.)
[This is the chief carrier of sleeping sickness in Nature. It is found in places over the whole of West Africa from the mouth of the Senegal River to Angola, and extends eastwards into the Bahr-el-Ghazal. The eastern boundary follows the valley of the Nile and includes the eastern shores of Lakes Victoria and Tanganyika; from the southern end of the lake the boundary tends south-west, approximately following the frontier between North-eastern Rhodesia and the Congo Free State, and passing through the Katanga district of the latter country into Angola (Austen). It may occur up to 3,000ft.; but, according to Bagshawe, it has not been recorded above 4,000ft. It feeds on the blood of many animals, including reptiles, amphibia, birds, and even amphibious fishes, as well as all the wild mammals. It seems, however, to possess a decided predilection for man, and undoubtedly thrives better upon mammals and birds than upon cold-blooded animals.
[It is not usually found far from water, requiring a humid atmosphere and temperature of about 85°F. (shade). But a marked seasonal distribution is shown, the flies considerably extending their range during the rainy season, and thus visiting districts which are dry for the greater part of the year; as the rains diminish the fly gradually leaves the temporary haunts and returns to the more permanent ones. It bites only by day, and then only in sunny weather, and usually lives in shade.
[Roubaud has shown that the first larva produced is about three weeks after copulation, and that others are produced at an interval of nine or ten days. The puparium stage is rapidly produced after the expulsion of the larva, often in
[Bruce has shown that only a very small percentage of flies fed experimentally on infected animals ultimately become infective, and that the infectivity of this small percentage depends upon a delayed infection of the salivary glands.
[A variety, wellmani of Austen, is found in Angola, Gambia, the Katanga district of the Congo Free State, the Matondwi Islands of Tanganyika, etc.
Glossina morsitans, Westwood.
[This species has been shown by Kinghorn and Yorke, and also by Bruce, to be responsible for the transmission of Trypanosoma rhodesiense, the micro-organism producing sleeping sickness in man in Rhodesia and Nyasaland and also in parts of German and Portuguese East Africa. Fisher and Taute have demonstrated experimentally that Trypanosoma gambiense—the sleeping sickness parasite of other parts of Africa—may also be transmitted by this fly, and in addition it is known to be capable of disseminating several species of trypanosomes pathogenic to animals. Of these, T. brucei (=? T. rhodesiense), the parasite of tsetse disease, first incriminated by Bruce, is perhaps the most important.
Fig. 420.—The tsetse-fly (Glossina morsitans, Westwood).
[It is the most widely spread of all tsetse-flies; its range extends from Senegambia in the north-west to Southern Kordofan and Southern Abyssinia in the north-east, and then southwards to the Bechuanaland Protectorate, North-eastern Transvaal and Zululand. The actual localities given by Austen are Gambia, French Guinea, Gold Coast, Togoland, Dahomey, Northern Nigeria, Congo Free State, the Bahr-el-Ghazal, the Uganda Protectorate, German East Africa, and Portuguese East Africa.
[This species is confined to “belts,” often of very limited extent, and appears to prefer regions where there is sufficient vegetation for moderate but not excessive cover and a hot, moderately dry climate. It is not nearly so dependent upon
[The structure of the male genitalia of those representatives of G. morsitans occurring on the West Coast of Africa and in parts of the Soudan presents certain constant differences from that of the typical form of this species; this form is known as G. morsitans, race submorsitans, Newst.
Genus. Stomoxys, Geoffroy.
[The members of this genus which occur in temperate and tropical countries are provided with a hard, slender, shiny black proboscis which projects horizontally from beneath the head; by means of this structure they can bite severely. In general appearance they resemble house flies, but the proboscis at once distinguishes them. In many parts of Britain they are known as storm flies on account of their frequent appearance indoors previous to a storm of rain or wind, which I have invariably found to be correct; they are also called stinging flies. In colour they are greyish, dusky or brownish-grey or black, varying from 5 to 7mm. in length; the thorax has dark longitudinal stripes and the abdomen dark spots or bands. In the male the eyes are closer together than in the female. These flies usually occur in stables and farmyards, along woods and in lanes, and mainly attack mammals.
Fig. 421.—The stinging fly (Stomoxys calcitrans, Linn.).
[One species (Stomoxys calcitrans, LinnÆus) occurs practically all over the world. The female lays her eggs in moist, warm, decaying vegetation; as many as eighty may be laid by a single female. The ova are white, banana-shaped, with a broad groove on the shorter curvature; they may hatch in two or three days. The creamy-white larva tapers to a point at the head end, and is truncated at the tail end. Two black mouth hooks are plainly visible at the cephalic extremity. There are two plates on the posterior surface of the last segment which bear the respiratory pores, nearly circular in outline. It reaches maturity in fourteen to twenty-one days; when mature it is 11mm. long. The pupal stage is passed in the old larva
[This insect may act as a carrier of anthrax, and has been proved to be the agent of an extensive epidemic of malignant pustule in the Isle of Pines, New Caledonia.425
[NoÈ’s426 experiments tend to show that it is an intermediate host and transmitter of Filaria labiato-papillosa of the ox.
[Surra is generally stated to be transmitted by Stomoxys as well as Tabanus, and yet Nitzman in the Philippines obtained uniformly negative results in exhaustive experiments. Others have also been unsuccessful. Certainly Stomoxys can transmit the disease in French West Africa (Bonet and Roubaud), and mechanically has been proved to be capable of disseminating other trypanosomes (experimentally): sleeping sickness (T. gambiense); nagana (T. brucei); souma (T. cazalboui); and el debat (T. soudanense).
[S. calcitrans may also be a carrier of poliomyelitis (Rosenau and Brues, Harvard Alumni Bulletin, 1912, xv, No. 9, pp.140–142). Several species are now known (S. brunnipes, GrÜnb.; S. inornata, GrÜnb.; S. nigra, Macq.; S. omega, Newst.; S. ochrosoma, Speiser, etc.).
Genus. Lyperosia, Rondani.
[A genus of small flies which bite man and animals, but are not so far connected with the transmission of any disease in man, but in Java it appears to carry surra (P. Schat, Meeledeel Praefstation Oost-Java, 1903, 3e ser., No. 44), the species being Lyperosia exigua, Meijere. These flies can be told from Stomoxys by the palpi being broader, flattened laterally, and as long, or nearly so, as the proboscis. When not feeding the palpi enclose the proboscis, as in Glossina. They are usually about half the size of Stomoxys, and are the smallest blood-sucking MuscidÆ. They frequently swarm around and upon domesticated animals.
[The life-history of the horn fly in America (L. irritans, Linn.) is well known. It lays its ova singly in freshly dropped cow-dung, and there the maggots feed, pupating in the soil beneath.
[Patton and Cragg also give some details as to the life-history of Liperosia exigua (“Medical Entomology,” p.375) as follows: “L. exigua, whose habits have been observed in Madras, usually lays twelve eggs at a time. The flies immediately return to the cow and the process is repeated when the dung is again dropped. The larvÆ migrate from the dung when about to pupate, and the puparia are always found in the earth at some distance away or under the sides of the patch of dung. The fly usually hatches out in five days, though sometimes as late as the eighth. Weiss has studied the life-history of irritans var. weisii from Algeria; its larval stage lasts five days, and the flies hatch out of the puparia in another five days.”
[The other biting genera of MuscidÆ, HÆmatobia, HÆmatobosca, Bdellolarynx, Stygeromyia, and PhilÆmatomyia, although sometimes annoying to man, have not in any way been connected with any disease.
[The horse fly (HÆmatobia irritans, L.427) attacks cattle chiefly, but now and then man is bitten. The different species can be told from Stomoxys by the palpi being nearly as long as the proboscis.
[The genus PhilÆmatomyia, Austen, is intermediate between Stomoxys and Musca in structure, and between the non-blood-sucking Musca, as M. domestica, and the blood-sucking Musca pattoni, Austen, which feeds on the blood exuding from the bites of true blood-suckers. They occur in Central Africa and India, Ceylon and Cyprus (vide “The Life-history of PhilÆmatomyia insignis, Austen,” Ann. Trop. Med. and Par., 1912, v, p.515).
[Two flies belonging to the family AnthomyidÆ also attack man, namely:—
[HydrotÆa meteorica, L. (the meteoric fly). This fly attacks man as well as animals. They especially bite around the eyes and nostrils of animals, but are not so particular with man; the head, however, is usually chosen. LinnÆus called it the meteoric fly because it often forms clouds around horses’ heads at the approach of rain. The HydrotÆas are usually black or blue-black in colour with bare eyes and simple abdomen, the front femora peculiarly constructed. H. meteorica, L., occurs in Britain.
[The members of the genus Hydrophoria, Desvoidy, also bite man.
Pupipara or EproboscidÆ.
[The Pupipara are all blood-suckers, the majority occurring as parasites on mammals and birds, where they are more or less permanent parasites. Occasionally some may attack man. They all produce their young fully formed, and they assume the pupal stage immediately after extrusion. The puparia are large. They are mostly flat, louse-like flies which may or may not be winged. In the case of Melophagus I have found the puparia are often passed by the female. The winged forms have a short quick flight, and when disturbed will seek shelter in man’s hair or beard. Two main families occur: (1) the HippoboscidÆ, and (2) the NycteribiidÆ. The former occur on animals and birds, the latter on bats only, but may invade man. Two other families are known—the BraulidÆ (bee parasites) and the StreblidÆ (bat parasites).
[The mouth of the HippoboscidÆ is long and sharp, forming a proboscis. The thorax and abdomen are flat and leathery. The legs are stout and strong, and terminate in large dentate claws and other structures of use in holding on to the hair or feathers of their host when blood-sucking.
[Austen says it is probable that the HippoboscidÆ are descended from ancestors belonging to the MuscidÆ, which underwent modification in bodily structure as the consequence of the adoption of a parasitic mode of life.
[Two wings are present in the true HippoboscÆ, Hippobosca equina (of the horse), H. camelina (of the camel), H. maculata (of oxen), and H. capensis (of dogs), but are absent in Melophagus, the sheep tick or ked fly (M. ovinus).
[In two genera, Lipoptena and Echestypus, wings are at first present, but are lost as soon as the fly finds its permanent host.
[With regard to their biting man, such is only occasional. I have known sheep shearers to be badly bitten by Melophagus ovinus, and have more than once been attacked myself when standing where shearing is taking place. Sharp records the grouse parasite, Ornithomyia lagopodis, as once biting severely a gamekeeper in Scotland. There are also records of H. maculata biting man in Africa and India.
[Although so far not connected with any human disease, it is interesting to note Theiler has shown that Hippobosca rufipes, v. Olfers, and H. maculata, Leach, are capable of transmitting Trypanosoma theileri, Laveran, the cause of gall sickness amongst cattle in the Transvaal. It is now considered, however, that Trypanosoma theileri is non-pathogenic, and that the cause of gall sickness is a piroplasma-like organism known as Anaplasma marginale. Theiler, Laveran and
[Lynchia.—Three members of this genus have been shown to transmit the non-pathogenic (?) organism, HÆmoproteus columbÆ amongst pigeons in Algeria and S. America.
Insects and Epidemic Poliomyelitis.
[In a recent number of the Journal of Economic Entomology,428 Brues and Sheppard point out the possibility of acute epidemic poliomyelitis (infantile paralysis) being an insect-borne disease. They summarize as follows:—
[Many facts connected with the distribution of cases and the spread of epidemics of this disease with histories of insects bites, suggest at least that the disease may be insect-borne. Field work during the past summer, together with a consideration of the epidemiology of the disease so far known, points strongly towards biting flies as possible carriers of the virus. It seems probable that the common stable fly (Stomoxys calcitrans, L.) may be responsible to a certain extent for the spread of acute epidemic poliomyelitis, possibly aided by other biting flies such as Tabanus lineola. No facts which disprove such a hypothesis have as yet been adduced, and experiments based upon it are now in progress.
[If the disease should prove to be common to any species of domestic animals, as is now strongly suspected, a secondary connection of ticks in spreading the disease among such animals seems probable, as has been mentioned.
[The following is some of the more important literature on Diptera in general: Meigen, J.W., “Syst. Besch. d. bek. europ. zweiflÜgligen insecten,” 1818–1838, 7 vols.; Brauer, F., “Monographie der Oestriden,” Wien, 1863; Idem, “Nachtr. hiersu,” Wien. ent. Zeit., 1887, vi, pp.4, 71; Schiner, J.R., “Fauna austriaca: die Fliegen,” Wien, 1860–64; LÖw, Fr., “Ueber Myiasis und ihre Erzeuger,” Wien. med. Wochenschr., 1882, xxii, p.247; 1883, xxxiii, p.972; Joseph, G., “Ueb. Fliegen als SchÄdlinge und Parasiten des Menschen,” Deutsch. med. Zeit., 1885, i, p.37; 1887, iii, pp.713 and 725; Peiper, E., “Fliegenlarven als gelegentl. Paras. d. Mensch.,” Berlin, 1900; Theobald, F.V., “Monograph of the CulicidÆ of the World,” 1901–1911, 5 vols. and 1 atlas, plates; Austen, E., “A Monograph of Glossina Tsetse-flies,” 1903, 1 vol.; Van der Wulp, “Diptera neerlandica,” 1877; Walker, “Insecta Britannica: Diptera,” 1851–53 and 1856; Lundbeck, “Diptera danica,” 1907–12; Zetterstedt, “Diptera scandinaviÆ,” 1850; Theobald, “British Flies,” 1892; Aldrich, “N. American Diptera,” 1905; Loew and Osten Sacken, “Monographs of the N. American Diptera,” 1862–63 and 1869; Macquart, “Diptera exotique,” 1830–47; Rondani, “Diptera exotica et Italica,” 1863–68; Williston, “Manual of Families and Genera of N. American Diptera,” second edition; Verrall, “British Flies.” A fuller literature will be found in Peiper, as well as in Huber’s “Bibliographie d. klin. Ent.,” 1899, iii, Jena, in the Bibliography at the end of this work and in the Rev. of App. Ent. (Dulau and Co., London), where all references to modern research can be found.—F.V.T.]
ADDENDA.
Akamushi or Kedani Sickness (vide also p.487).—Schuffner (Far East. Assoc. Trop. Med., Compt. rend. Trois. Cong. Biennial, 1913, Saigon, 1914, pp.309–315) states he observed a peculiar fever in Deli, Sumatra, somewhat resembling typhoid. This he traced either to a mite or tick. He figures the possible carriers, namely, a Trombidium and CheyletidÆ. He calls this disease pseudo-typhus—a variant of Japanese kedani sickness, which, he says, also occurs in the Philippines.
Ticks.—African Tick Fever: Marzinovsky (Proc. of Conference of Bacteriologists and Representatives of Medical Sanitary Authorities on the Campaign against Infectious Diseases in connection with the War, Soc. Russ. Physicians in mem. Pirosov, Moscow, 1915, pp.56–68), states that African tick fever has been imported into Persia, and that it is there carried by Ornithodorus tholosani.
Tick Paralysis: Todd (“Paralysis and Tick-bite,” Can. Med. Assoc. Journ., 1914, iv, No. 9, pp.825–826) refers to paralysis ascribed to the bites of ticks in children, and possibly adults, in America, British Columbia and Australia. He states that a young child, perfectly well one day, has more or less complete paresis or paralysis on the next, fever, a rapid pulse, and other constitutional symptoms. The child may be dull and stupid, and may have convulsions. If the tick is not found and removed the child may die, but if it is removed, the symptoms disappear and recovery is complete in a few hours. The tick must be entirely removed.
Diptera.—PsychodidÆ: Bolt (China Med. Journ., Shanghai, xxix, No. 2, pp.78–86) states that sand-flies (Plebotomus) and the fever due to them are common in North China, May and June being the worst months. The natives of the region appear to be immune, but all others suffer. Old ruined buildings are the favourite haunts of the Phlebotomus. The species of Phlebotomus has not been determined.
PulicidÆ.—Dermatophilus (Sarcopsylla) penetrans, or the “Jigger.”—This flea (vide p.544) is believed by Lama (Giorn. Ital. Mal. Ven., Milan, 1914, xlix, pp.465–472) frequently to carry leprosy and he points out that the early lesions of leprosy usually appear on the uncovered parts of the body. This flea also attacks rats.
Brachycera.—LeptidÆ (vide p.603): White, A. (
Pycnosoma putorium: This is believed by Roubaud (“Les Producteurs de Myiases et Agents similaires chez l’homme et les animaux,” Paris, 1914, part I) to be largely concerned in the spread of amoebic dysentery in French West Africa.
Lucilia argyrocephala, Macquart: This green-bottle fly is described by Roubaud as producing myiasis in Africa (“Les Producteurs de Myiases et Agents similaires chez l’homme et les animaux,” 1914, Paris, part I). It attacks ulcers and sores in man and animals.
Auchmeromyia luteola, Fabr.: Schwetz (Ann. Trop. Med. and Par., 1914, viii, No. 3, pp.497–507), collected a large quantity of this insect at Kabinda. He placed them in flasks with sand and a few days later they pupated, and in fifteen days several flies hatched out. The larval period varies from an unknown minimum up to several months. The larva may live for at least two months without food. A female oviposited on the 17th, and on the 18th one larva hatched. The pupal stage seems to last eight to fifteen days. The larvÆ appear to bite by day as well as night according to native information.
Cordylobia anthropophaga, GrÜnb.: Roubaud (“Etudes sur la Faune parasitaire de l’Afrique occidentale franÇaise,” part I, “Les Producteurs des Myiases et Agents similaires chez l’homme et les animaux,” Paris, 1914) gives the life-history of this species. One fly laid 150 ova in a glass vessel, on the sides, and on some rotten fruit, and died the following day. He found that fifteen larvÆ just hatched placed on sand in a glass vessel with a guinea-pig gave rise to characteristic tumours on the ventral surface of the body and the anus. Other experiments failed. It thus seems that infection takes place from larvÆ which have hatched apart from the host. Infection of man is regarded as accidental; no positive infection of horses, oxen, sheep or pigs is known—it is rare in goats, and poultry never seem to be attacked. The result of experiments tends to show that the apparent choice of a host is mainly a question of body temperature. The larva, whether freshly emerged or eight to ten days old, penetrates the skin immediately, boring obliquely between the epidermis and dermis. Once removed from the tumour the maggot cannot bore again. The first moult takes place about three days after penetration, and the total period of residence in the host is seven to eight days. Upon emerging the larva falls to the ground and buries itself. In two or three days it pupates and this stage lasts no longer than twenty days. High temperatures, such as 95°F., appear to be fatal.
Myiasis.—Coates, G.M., “A Case of Myiasis Aurium accompanying the Radical Mastoid Operation,” Journ. Amer. Med. Assoc., Chicago, Ill., 1914, lxiii, pp.479–480: Apparently C. macellaria, forty to fifty coming away with the gauze after the operation.
Huber, G.U., and Flack, F.L., “An Unusual Case of Screw-worms in the Nose and Nasal Accessory Sinuses,” Journ. Amer. Med. Assoc., Chicago, 1914, lxiii, pp.2288–2289.
Auricular Myiasis.—Francaviglia, M.C., “An cora sulla myiasi auricolare,” Boll. Sedute Accad. Gioenia, Catania, 1914, No. 31, pp. 15–23. This writer mentions the following parasites in the human ear: Sarcophaga carnarÍa, L.; Wohlfartia magnifica, Schiner; Chrysomyia macellaria, F.; Calliphora vomitoria, L.; and Anthomyia pluvialis, L. He refers to a severe myiasis in Russia, due to a fly variously recorded as Sarcophaga wohlfarti, Rond.; S. ruralis, Meig.; or Sarcophila meigeni, Portsch. These are all probably synonyms of W. magnifica. Chrysomyia macellaria, in Central America and South America, is quite as harmful as S. carnaria, causing perforation of the tympanum and meningitis. Lucilia nobilis and L. cÆsar have also been incriminated. Of the sub-family AnthomyinÆ, the larvÆ of Fannia scalaris, Meig., F. canicularis, Meig., F. incisurata, Zett, and HydrotÆa meteorica, L., are chiefly associated with myiasis. He recommends, if the larvÆ are outside the tympanum, an injection of chloroform vapour by a few drops of water saturated with chloroform, by an emulsion of 5 per cent. carbon bisulphide or with benzine. When detached they may be removed with forceps or a solution of boric acid. If the tympanum has been perforated, the larvÆ must be removed at once.
Francaviglia also records the larva of Oestrus ovis in the human ear (Boll. Sedute Accad. Gioenia, Catania, 1914, No. 31, pp.23–27).
Body, Head, and Clothes Lice.—Lobaczewski (Wien. klin. Wochenschr., Vienna, 1915, xxviii, pp.373–374) recommends the impregnation of body linen with a 30 per cent. solution of oleum betÆ in 96 per cent. alcohol as an efficient method of keeping the body free of lice. But the process must be renewed each time the linen is washed and it takes fifteen minutes to carry out. On adding the oil to the alcohol, a portion of the former is precipitated, the supernatant fluid is decanted and poured over the linen, which is wrung out in it and dried. The garments retain their lice-proof properties until washed. Three days after wearing the clothes thus treated no lice remain on the body.
Portnikov, Proc. of Conference of Bacteriologists and Representatives of Medical Sanitary Authorities on the Campaign against Infectious Diseases in connection with the War, Soc. Russ. Physicians in mem. Pirosov, Moscow, 1915, p.131.
Pediculus capitis and Phthirus pubis are shown to be successfully controlled by applying spirit extract of sabadilla and both white and grey mercury ointment, solution of corrosive sublimate of a strength of 1 in 250 to 1 in 100, amyl and ethyl alcohol, benzine, chloroform, carbon tetrachloride, methane, birch tar, liquid of malinin, etc. The control of Pediculus vestimenti by the mixture of tartaric acid and sodium sulphite slightly moistened with water is advised. It is placed in small linen bags underneath the shirt; the heat of the body produces a reaction which continues for two days, giving off a large amount of SO2, which spreads beneath the shirt and kills all the parasites but does not affect the skin. Marzinovsky, in the same Proceedings (pp.56–68), gives a number of remedies for Pediculus vestimenti (called humanus), and mentions quinine or mercury, which latter the natives in Turkestan carry on their hands and legs in bracelets soaked in mercury compounds. He also mentions ethereal oils, the most effective being clove oil, eucalyptus, oil of anise and camphor. He recommends for disinfecting clothing for army purposes the chamber used by the Japanese on a large scale. Kummerfelds’ wash is advised, and is prepared as follows: 20 parts of precipitated sulphur are incorporated in a mortar with 50 parts of glycerine; 2 parts of camphor are separately ground with 50 of eau-de-Cologne and 20 of borax, and 870 parts of distilled water are added; the whole is mixed together and 3 drops of an extract of musk are added; shake in order to prevent the sulphur settling down; 50 parts of ether are added to the mixture. This sounds an expensive and troublesome preparation to make.
Shipley A.E., “Flowers of Sulphur and Lice,” Brit. Med. Journ., 1915, p.295. It is here stated by Dr. Lounsbury that the South African troops were supplied by the Government with bags of flowers of sulphur sewn in small calico bags and secured to the underclothing next the skin as a preventive of lice. The bags were 2in. square, one on the trunk and one against each leg. This is a generally accepted preventive, but is best mixed with equal parts of creosote and naphthalene.
Shipley, A.E., “Insects and War,” Brit. Med. Journ., September 19 to November 14, 1914. General advice given re lice.
