Bacteriology as a science is a development of the latter half of the nineteenth century. It may be said to have begun in the decade between 1870 and 1880, due largely to the wide circulation given to Koch’s work in proving that Bacillus anthracis is the cause of Anthrax in 1876, in devising new culture methods and in demonstrating that wound infections are due to microÖrganisms, 1878. Associated with this work were the great improvements in the microscope by AbbÉ and the introduction of anilin dyes for staining bacteria by Weigert. These results attracted workers throughout the world to the “new science.” Nevertheless, this work of Koch’s was preceded by numerous observations and experiments which led up to it. Certainly the most important discoveries immediately responsible were those of Pasteur. He must be considered as the greatest of the pioneer bacteriologists since he worked in all fields of the subject. Some of the antecedent work was done in attempting to disprove the old “spontaneous generation” theory as to the origin of organisms; some in searching for the causes of disease and some in the study of fermentation and putrefaction.

SPONTANEOUS GENERATION.

Speculation as to the first origin of life is as old as history and doubtless older. Every people of antiquity had its own legends, as for example, the account in Genesis. This question never can be definitely settled, even though living matter should be made in the laboratory. The doctrine of the “spontaneous origin” of particular animals or plants from dead material under man’s own observation is a somewhat different proposition and may be subjected to experimental test. The old Greek philosophers believed it. Anaximander (B.C. 610–547) taught that some animals are derived from moisture. Even Aristotle (B.C. 384–322) said that “animals sometimes arise in soil, in plants, or in other animals,” i.e., spontaneously. It can be stated that this belief was general from his day down through the Dark and Middle Ages and later. Cardano (A.D. 1501–1576) wrote that water gives rise to fish and animals and is also the cause of fermentation. Van Helmont (1578–1644) gives directions for making artificial mice. Kircher (1602–1680) describes and figures animals produced under his own eyes by water on plant stems.

However, many thinkers of the seventeenth century doubted the truth of this long-established belief. Francesco Redi (1626–1698) made a number of experiments which tended to prove that maggots did not arise spontaneously in meat, as was generally believed, but developed only when flies had an opportunity to deposit their eggs on the meat. It seems that by the latter part of this century the idea that organisms large enough to be seen with the naked eye could originate spontaneously was generally abandoned by learned men.

The work of Leeuwenhoek served to suspend for a time the subject of spontaneous generation, only to have it revived more vigorously later on. He is usually called “The Father of the Microscope,” though the compound microscope was invented probably by Hans Zansz or his son Zacharias, of Holland, about 1590. Leeuwenhoek used a simple lens, but his instruments were so much more powerful that they opened up an entirely new and unknown world. (Fig.1.)

Anthony van Leeuwenhoek (1632–1723) was apprenticed to a linen draper and accumulated a comfortable fortune in this business. He became interested in the grinding of spectacle lenses, then an important industry in Delft, Holland, where he lived, and did a great deal of experimental work in this line, mainly for his own enjoyment. Finally he succeeded in making a lens so powerful that he could see in water and various infusions very minute living bodies never before observed. Leeuwenhoek contributed 112 papers to the Royal Society of Great Britain, the first in 1673, many of them accompanied by such accurate descriptions and drawings, for example a paper submitted September 12, 1683, that there is no doubt that he really saw bacteria and was the first to do so (Fig.2). Rightly may he be styled “The Father of Bacteriology,” if not of the microscope. He says in one paper: “With the greatest astonishment I observed that everywhere through the material I was examining were distributed animalcules of the most microscopic dimness which moved themselves about in a remarkably energetic way.” Thus he considered these living objects to be animals, from their motion, and this belief held sway for nearly two hundred years.

Leeuwenhoek was a pure observer of facts and made no attempt at speculation, but his discoveries soon started the theorists to discussing the origin of these minute organisms. Most observers, as was probably to be expected, believed that they arose spontaneously. Needham, in 1749, described the development of microÖrganisms around grains of barley in water. Bonnet, in 1768, suggested that probably Needham’s animalcules came from ova in the liquid. The Abbot Spallanzani, in 1769, called attention to the crudeness of Needham’s methods and later, in 1776, attempted to disprove spontaneous origin by heating infusions of organic material in flasks and then sealing them. His critics raised the objections that heating the liquids destroyed their ability to support life, and that sealing prevented the access of fresh air which was also necessary. The first objection was disproved by the accidental cracking of some of the flasks which thereafter showed an abundant growth. This accident seemed also to support the second objection, and Spallanzani did not answer it. Though Spallanzani’s experiments failed to convince his opponents, they led to important practical results, since FranÇois Appert, in 1810, applied them to the preserving of fruits, meats, etc., and in a sense started the modern canning industry.

From Spallanzani to Schultze, there were no further experiments to prove or disprove spontaneous generation. Schultze, in 1836, attempted to meet the second objection to Spallanzani’s experiment, i.e., the exclusion of air, by drawing air through his boiled infusions, first causing it to bubble through concentrated sulphuric acid to kill the “germs” (Fig.3.). His flasks fortunately showed no growths, but his critics claimed that the strong acid changed the properties of the air so that it would not support life. This experiment of Schultze’s, though devised for a different purpose, was really the first experiment in the use of chemical disinfectants, though Thaer (page 31) had used chemicals in a practical way. Schwann, in 1837, modified this experiment, by drawing the air through a tube heated to destroy the living germs (Fig.4). His experiments were successful but the “spontaneous generation” theorists raised the same objection, i.e., the change in the air by heating. This was the first experiment in which the principle of “dry heat” or “hot air” sterilization was used. Similar arguments were brought forward, also to the use of cotton plugs as filters by Schroeder and Dusch in 1859 (Fig.5). This was the first use of the principle of sterilization by filtration. It remained for Chevreuil and Pasteur to overcome this objection in 1861 by the use of flasks with long necks drawn out to a point and bent over. These permitted a full access of air by diffusion but kept out living germs, since these cannot fly but are carried mechanically by air currents or fall of their own weight (Fig.6.). Hoffman, the year before (1860), had made similar experiments but these remained unnoticed. The Pasteur flasks convinced most scientists that “spontaneous generation” has never been observed by man, though some few, notably Dr. Charlton Bastian, of England, vigorously supported the theory from the early seventies until his death in November, 1915.

John Tyndall, in combating Bastian’s views showed that boiled infusions left open to the air in a closed box through which air circulated did not show any growth of organisms provided the air was so free of particles that the path of a ray of light sent through it from side to side could not be seen (Fig.7). Or if such sterilized infusions were exposed to dust-free air, as in the high Alps, the majority showed no growth, while all infusions in dusty air did show an abundance of organisms. Tyndall’s experiments confirmed those of Pasteur and his predecessors and showed that the organisms developed from “germs” present in the air falling into the liquids and not spontaneously.

While Tyndall’s experiments were of great value as indicated, they probably were harmful in another way. These “germs in the air” were considered by bacteriologists as well as laymen to include necessarily many disease germs and to indicate the very general, if not universal, presence of these latter in the air. This idea led to many erroneous practices in sanitation and disinfection which even to this day are not eliminated.

CAUSATION OF DISEASE.

The transmission of disease from person to person was recognized by the ancients of European and Asiatic countries. Inoculation of smallpox was practiced in China and India probably several thousand years ago and was introduced by Lady Mary Wortley Montague into England in 1721, from Constantinople. These beliefs and practices do not seem to have been associated with any speculations or theories as to the cause of the disease. Apparently the first writer on this subject was Varo, about B.C. 70, who suggested that fevers in swampy places were due to invisible organisms. The treatment of wounds during the thirteenth and fourteenth centuries by hot wine fomentations and by the application of plasters was based on the theory that the air brought about conditions in the wounds which led to suppuration. These practices were indeed primitive antisepsis, yet were not based on a germ theory of the conditions which were partially prevented. Fracastorius (1484–1553), in a work published in 1546, elaborated a theory of “disease germs” and “direct and indirect contagion” very similar to modern views, though based on no direct pathological knowledge. Nevertheless Kircher (mentioned already) is usually given undeserved credit for the “contagium vivum” theory. In 1657 by the use of simple lenses he observed “worms” in decaying substances, in blood and in the pus from bubonic plague patients (probably rouleaux of corpuscles in the blood, certainly not bacteria in any case). Based on these observations and possibly also on reading the work of Fracastorius, his theory of a “living cause” for various diseases was published in 1671, but received little support.

The discoveries of Leeuwenhoek which proved the existence of microscopic organisms soon revived the “contagium vivum” idea of Kircher. Nicolas Andry in a work published in 1701 upheld this view. Lancisi in 1718 advanced the idea that “animalcules” were responsible for malaria, a view not proved until Laveran discovered the malarial parasite in 1880.1 Physicians ascribed the plague which visited Southern France in 1721 to the same cause, and many even went so far as to attribute all disease to animalcules, which brought the theory into ridicule. Nevertheless the “contagium vivum” theory survived, and even Linnaeus in his Systema NaturÆ (1753–6) recognized it by placing the organisms of Leeuwenhoek, the contagia of diseases and the causes of putrefaction and fermentation in one class called “Chaos.” Plenciz, a prominent physician and professor in the Vienna Medical School, published in 1762 a work in which he gave strong arguments for the “living cause” theory for transmissable diseases. He taught that the agent is evidently transmitted through the air and that there is a certain period of incubation pointing to a multiplication within the body. He also believed that there was a specific agent for each disease. His writings attracted little attention at the time and the “contagium vivum” theory seems to have been almost lost sight of for more than fifty years. Indeed, Oznam, in 1820, said it was no use to waste time in refuting hypotheses as to the animal nature of contagium.

Isolated observers, were, however, keeping the idea alive, each in his own locality. In 1787 Wollstein, of Vienna, showed that the pus from horses with glanders could infect other horses if inoculated into the skin. Abilgaard, of Copenhagen, made similar experiments at about the same time. In 1797 Eric Viborg, a pupil of Abilgaard’s, published experiments in which he showed the infectious nature not only of the pus but also of the nasal discharges, saliva, urine, etc., of glandered horses. Jenner in 1795–98 introduced vaccination as a method of preventing smallpox. This epoch-making discovery attracted world wide attention and led to the overcoming of this scourge which had devastated Europe for centuries, but contributed little or nothing to the question of the causation of disease. Prevost’s discovery of the cause of grain rust (Puccinia graminis) in 1807 was the first instance of an infectious disease of plants shown to be due to a microscopic plant organism, though not a bacterium in this case.

Doubtless one reason why the work on glanders and grain rust attracted little attention among the practitioners of human medicine was owing to the prevalent belief in man’s complete separation from all lower forms of life. The evolutionists had not yet paved the way for experimental medicine.

In 1822 Gaspard showed the poisonous nature of material from infected wounds by injecting it into animals and causing their death. Tiedemann (1822), Peacock (1828) described “little bodies” in the muscles of human cadavers which Hilton (1832) considered to be parasitic in nature. Paget (1835) showed that these bodies were round worms and Owen (1835) described them more accurately and gave the name Trichina spiralis to them. Leidy (1846) found organisms in the muscles of hogs which he considered to be the same as Owen’s Trichina and paved the way for the work of Zenker (1860) in showing the pathological relation between the Trichina of pork and human Trichinosis. Bearing on the “contagium vivum” theory was the rediscovery of the “itch mite” (Sarcoptes scabiei) by Renucci (1834), an Italian medical student. This had been declared several hundred years before but had been lost sight of. Chevreuil and Pasteur, in 1836, showed that putrefaction did not occur in meat protected from contamination, and suggested that wound infection probably resulted from entrance of germs from without. Bassi, investigating a disease of silkworms in Italy, demonstrated that a certain mold-like fungus (Botrytis bassiana) was the cause in 1837. This was the first instance of a microscopic vegetable organism proved to be capable of causing disease in an animal.

Boehm, in 1838, observed minute organisms in the stools of cholera patients and conjectured that they might have a causal connection with the disease. Dubini of Milan in 1838 discovered the Ankylostoma duodenale which later was further described by Omodei in 1843 and shown to be the cause of Egyptian chlorosis by Griesinger (1851). The fungous nature of favus, a scalp disease, was recognized by SchÖnlein in 1839, and the organism was afterward called “Achorion schoenleinii.” Berg, in 1839–41, showed that thrush is likewise due to a fungus, “Oidium albicans.”

These discoveries led Henle, in 1840, to publish a work in which he maintained that all contagious diseases must be due to living organisms, and to propound certain postulates (afterward restated by Koch and now known as “Koch’s postulates” p.233) which must be demonstrated before one can be sure that a given organism is the specific cause of a given disease. The methods then in vogue and the instruments of that period did not enable Henle to prove his claims, but he must be given the credit for establishing the “contagium vivum” theory on a good basis and pointing the way for men better equipped to prove its soundness in after years.

In 1842–43 Gruby showed that Herpes tonsurans, a form of ringworm, is due to the fungus Trichophyton tonsurans. Klencke, in 1843, produced generalized tuberculosis in a rabbit by injecting tuberculous material into a vein in the ear, but did not carry his researches further. In 1843, Doctor Oliver Wendell Holmes wrote a paper in which he contended that puerperal fever was contagious. Liebert identified the Peronospora infestans as the cause of one type of potato rot in 1845. The skin disease Pityriasis (tinea) versicolor was shown to be due to the Microsporon furfur by Eichstedt in 1846. In 1847 Semmelweiss of Vienna recommended disinfection of the hands with chloride of lime by obstetricians because he believed with Holmes in the transmissibility of puerperal fever through poisons carried in this way from the dissecting room but his theories were ridiculed.

Pollender, in 1849, and Davaine and Rayer, in 1850, independently observed small rod-like bodies in the blood of sheep and cattle which had died of splenic fever (anthrax). That Egyptian chlorosis, afterward identified with Old World “hookworm disease,” is caused by the Ankylostoma duodenale was shown by Greisinger in 1851. In the same year the Schistosomum hematobium was shown to be the cause of the “Bilharzia disease” by Bilharz. KÜchenmeister discovered the tapeworm, TÆnia solium, in 1852, Cohn, an infectious disease of flies due to a parasitic fungus (Empusa muscÆ) in 1855, and Zenker showed the connection between trichinosis of pork (“measly pork”) and human trichinosis (1860) as indicated above. The organisms just mentioned are, of course, not bacteria, but these discoveries proved conclusively that living things of one kind or another, some large, most of them microscopic, could cause disease in other organisms and stimulated the search for other “living contagiums.” In 1863 Davaine, already mentioned, showed that anthrax could be transmitted from animal to animal by inoculation of blood, but only if the blood contained the minute rods which he believed to be the cause. Davaine later abandoned this belief because he transmitted the disease with old blood in which he could find no rods. It is now known that this was because the bacilli were in the “spore” form which Davaine did not recognize. He thus missed the definite proof of the bacterial nature of anthrax because he was not familiar with the life history of the organism which was worked out by Koch thirteen years later. In 1865 Villemin repeatedly caused tuberculosis in rabbits by subcutaneous injection of tuberculous material and showed that this disease must be infectious also. In the same year Lord Lister introduced antiseptic methods in surgery. He believed that wound infections were due to microÖrganisms getting in from the air, the surgeon’s fingers, etc., and without proving this, he used carbolic acid to kill these germs and prevent the infection. His pioneer experiments made modern surgery possible. In this year also, Pasteur was sent to investigate a disease, Pebrine, which was destroying the silkworms in Southern France. He showed the cause to be a protozoan which had been seen previously by Cornalia and described by NÄgeli under the name Nosema bombycis and devised preventive measures. This was the first infectious disease shown to be due to a protozoan. In 1866 Rindfleisch observed small pin-point-like bodies in the heart muscle of persons who had died of wound infection. Klebs, in 1870–71, published descriptions and names of organisms he had found in the material from similar wounds, though he did not establish their causal relation. Bollinger, in 1872, discovered the spores of anthrax and explained the persistence of the disease in certain districts as due to the resistant spores. In 1873 Obermeier observed in the blood of patients suffering from recurrent fever long, flexible spiral organisms which have been named SpirochÆta obermeieri. LÖsch ascribed tropical dysentery to an ameba, named by him Amoeba coli, in 1875. Finally, Koch, in 1876, isolated the anthrax bacillus, worked out the life history of the organism and reproduced the disease by the injection of pure cultures and recovered the organism from the inoculated animals, thus establishing beyond reasonable doubt its causal relationship to the disease. This was the first instance of a bacterium proved to be the cause of a disease in animals. Pasteur, working on the disease at the same time, confirmed all of Koch’s findings, though his results were published the next year, 1877. Bollinger determined that the Actinomyces bovis (Streptothrix bovis) is the cause of actinomycosis in cattle in 1877. Woronin in the same year discovered a protozoan (Plasmodiophora brassicÆ) to be the cause of a disease in cabbage, the first proved instance of a unicellular animal causing a disease in a plant. In 1878 Koch published his researches on wound infection in which he showed beyond question that microÖrganisms are the cause of this condition, though Pasteur in 1837, had suggested the same thing and Lister had acted on the theory in preventing infection.

These discoveries, especially those of Koch, immediately attracted world-wide attention and stimulated a host of workers, so that within the next ten years most of the bacteria which produce disease in men and animals were isolated and described. It is well to remember that the first specific disease of man proved to be caused by a bacterium was tuberculosis, by Koch in 1882.

Progress was greatly assisted by the introduction of anilin dyes as suitable stains for organisms by Weigert in 1877, by Koch’s application of special technic and gelatin cultures for isolation and study, 1881, and the great improvements in the microscope by Prof. AbbÉ, of Jena.

Laveran’s discovery of the malarial parasite in 1880 turned attention to protozoa as the causes of disease and led to the discovery of the various piroplasmoses and trypanosomiases in man and the lower animals.

Pasteur’s protective inoculations in chicken cholera and anthrax directed attention to the possibility of using bacteria or their products as a specific protective or curative means against particular diseases. This finally led to the discovery of diphtheria antitoxin by Behring, and independently by Roux, in 1890, a discovery which opened up the wide field of immunity which is so persistently cultivated at the present time.

While the causation of disease by bacteria has probably attracted most attention, especially in the popular mind, it should not be forgotten that this is but one of the numerous ways in which these organisms manifest their activities, and in a sense it is one of their least-important ways, since other kinds are essential in many industries (dairying, agriculture) and processes (sewage purification) and are even indispensable for the very existence of all green plants and hence of animals, including man himself.

PUTREFACTION AND FERMENTATION.

The idea that there is a certain resemblance between some infectious diseases and the processes of putrefaction and fermentation seems to have originated during the discussion on spontaneous generation and the “contagium vivum” theory which followed Leeuwenhoek’s discoveries. Plenciz (1762) appears to have first formulated this belief in writing. He considered putrefaction to be due to the “animalcules” and said that it occurred only when there was a coat of organisms on the material and only when they increased and multiplied. Spallanzani’s experiments tended to support this view since his infusions did not “spoil” when boiled and sealed. Appert’s practical application of this idea has been mentioned.

Thaer, in his Principles of Rational Agriculture, published in the first quarter of the nineteenth century, expressed the belief that the “blue milk fermentation” was probably due to a kind of fungus that gets in from the air, and stated that he had prevented it by treating the milk cellars and vessels, with sulphur fumes or with “oxygenated hydrochloric acid” (hypochlorous acid).

In 1836 Chevreuil and Pasteur showed that putrefaction did not occur in meat protected from contamination. In 1837 Caignard-Latour, in France, and Schwann, in Germany, independently showed that alcoholic fermentation in beer and wine is due to the growth of a microscopic plant, the yeast, in the fermenting wort. C.J. Fuchs described the organism which is commonly called the “blue milk bacillus” in 1841 and conjectured that the souring of milk was probably bacterial in origin. It remained for Pasteur to prove this in 1857. During the following six or seven years Pasteur also proved that acetic acid fermentation, as in vinegar making, butyric acid fermentation (odor of rancid butter and old cheese) and the ammoniacal fermentation of urea, so noticeable around stables, were each due to different species of bacteria. Pasteur also, during the progress of this work, discovered the class of organisms which can grow in the absence of free oxygen—the anaËrobic bacteria. There is no question that Pasteur from 1857 on did more to lay the foundations of the science of bacteriology than any other one man. Influenced by Pasteur’s work von Hesseling, in 1866, stated his belief that the process of cheese ripening, like the souring of milk, was associated with the growth of fungi, and Martin also, in 1867, stated that cheese ripening was a process which was akin to alcoholic, lactic and butyric fermentations. Kette, in 1869, asserted the probability of Pasteur’s researches furnishing a scientific basis for many processes of change in the soil. In 1873 SchlÖsing and MÜntz showed that nitrification must be due to the action of microÖrganisms, though the discovery of the particular ones remained for Winogradsky in 1889. Thus the belief that fermentation and putrefaction are due to microÖrganisms was as well established by the early eighties of the last century as that similar organisms are the causes of infectious diseases.

STUDY OF FORMS.

An important part of the scientific knowledge of living organisms is dependent on a study of their forms and relationships. As has been stated, Leeuwenhoek considered bacteria to be “animalcules” because they showed independent movement. But little attention was paid to the natural history of these animalcules for nearly a hundred years after Leeuwenhoek. During the last quarter of the eighteenth century, however, workers busied themselves chiefly with the discovery and description of new forms. Among these students were Baron Gleichen, Jablot, Lesser, Reaumur, Hill and others. MÜller, of Copenhagen, in 1786 published the first attempt at classification, a most important step in the study of these organisms. MÜller introduced the terms Monas, Proteus and Vibrio, which are still in use. Ehrenberg, in his work on Infusoria, or the organisms found in infusions, published in 1838, introduced many generic names in use at present, but still classed the bacteria with protozoa. Joseph Leidy, the American naturalist, considered that the “vibrios” of previous writers were plants and not “animalcules.” He seems to have been the first to have made this distinction (1849). Perty (1852) recognized the presence of spores in some of his organisms. Ferdinand Cohn (1854) classed the bacteria among plants. NÄgeli (1857) proposed the name “Schizomycetes” or “fission fungi,” which is still retained for the entire class of bacteria. Cohn in the years 1872–1875 established classification on a modern basis and added greatly to the knowledge of morphology and natural history of bacteria. He described spore formation and the development of spores into active bacteria, and showed the close relationships as well as differences between the bacteria and the lower algÆ. Robert Koch was a pupil of Cohn.

An examination of the accompanying chronological table will show how the investigations and discoveries in connection with “spontaneous generation,” the “contagium vivum” theory and putrefaction and fermentation must have been mutually suggestive: