2 Some notable exceptions are found in the work of the Bath and West of England Society, Lord Vernon's model dairy, and the Essex County Council Bacteriological Teaching Laboratory.

3 We propose throughout to use the term bacterium (pl. bacteria) in its generic meaning, unless especially stated to the contrary. It will also be synonymous with the terms microbe, germ, and micro-organism. The term bacillus will, of course, be restricted to a rod-shaped bacterium.

4 Migula has recently (1896) suggested that the Schizomycetes should be subdivided into CoccaceÆ, BacteriaceÆ, SpirillaceÆ (spirilla, spirochÆta), ChlamydobacteriaceÆ (Streptothrix, Crenothrix, Cladothrix), and Beggiatoa.

5 A one-twelfth oil immersion lens is requisite for the study of the lower bacteria.

6 A flagellum is a hair-like process arising from the poles or sides of the bacillus. It must not be confused with a filament, which is a thread-like growth of the bacillus itself.

7 A "pure culture" is a growth in an artificial medium outside the body of one species of micro-organism only.

8 Some pathogenic germs (suppuration and typhoid) can withstand freezing for weeks.

9 G. J. Romanes, Darwin and After Darwin, vol. ii., 231.

10 It will be observed that there is a marked difference between the effects of dry heat and moist heat. Moist heat is able to kill organisms much more readily than dry, owing to its penetrating effect on the capsule of the bacillus. Dry heat at 140°C. (284°F.), maintained for three hours, is necessary to kill the resistant spores of Bacillus anthracis and B. subtilis, but moist heat at fifty degrees less will have the same effect. It is from data such as these that in laboratories and in disinfecting apparatus moist heat is invariably preferred to dry heat. For with the latter such high temperatures would be required that they would damage the articles being disinfected. Koch states the following figures for general guidance: Dry heat at a temperature of 120°C. (248°F.) will destroy spores of mould fungi, micrococci, and bacilli in the absence of their spores; for the spores of bacilli 140°C. (284°F.), maintained for three hours, is necessary; moist heat at 100°C. (212°F.) for fifteen minutes will kill bacilli and their spores.

11 Water from a house cistern is rarely a fair sample. It should be taken from the main. If taken from a stream or still water, the collecting bottle should be held about a foot below the surface before the stopper is removed.

12 The cubic centimetre (cc.) is a convenient standard of fluid measurement constantly recurring in bacteriology. It is equal to 16–20 drops, and 28 cc. equal one fluid ounce.

13 The gelatine is reduced to liquid form by heating in a water-bath. Before inserting the suspected water it is essential that the gelatine be under 40° C, or thereabouts, in order not to approach the thermal death-point of any bacteria.

14 Micro-organisms in Water (1894).

15 Report on the Micro-organisms of Sewage, Reports to L. C. C., 1894, No. 216.

16 Harben Lectures, 1896.

17 Report on the Metropolitan Water Supply.

18 The methods adopted for making a quantitative and qualitative examination of sewage are precisely analogous to those used in milk research. Dilution with sterilised water previous to plating out on gelatine in Petri dishes is essential (1 cc. to 10,000 cc. of sterile water, or some equally considerable dilution), otherwise the large numbers of germs would rapidly liquefy and destroy the film. Special methods must be used for the isolation of special organisms; phenol-gelatine, Elsner medium, indol reaction, "shake" cultures, Parietti broth, etc., must often be resorted to for special bacteria. Spores of bacteria may always be numerically estimated by adding the suspected water or sewage to gelatine, and then heating to 80°C. for ten minutes before plating out. This temperature removes the bacilli, but leaves the spores untouched.

19 The bacilli of typhoid can live in crude sewage (Klein), but only for a very short period. When sewage is diluted with large quantities of water the case is very different. Bacillus coli flourishes in sewage.

20 Annual Report of the Medical Officer of the Local Government Board, 1897–98, p. 210.

21 John Tyndall, F.R.S., Floating Matter of the Air.

22 FlÜgge has lately attempted to demonstrate that an air current having a velocity of four metres per second can remove bacteria from surfaces of liquids by detaching drops of the liquid itself.

23 Hewlett and Thomson graphically demonstrated the bactericidal power of the nasal mucous membrane by noting the early removal of Bacillus prodigiosus, which had been purposely placed on the healthy Schneiderian membrane of the nose.

24 Pathological Society of London, Transactions, 1897.

25 Annali d'Igiene Sperimentale, vol. v. (1895), fasc. 4.

26 Public Health, vol. x., No. 4, p. 130 (1898).

27 FlÜgge, Grundriss der Hygiene, 1897.

28 Zeitschrift fÜr Hygiene, vols. xxiv.-xxvi.

29 Annales de Micrographie.

30 E. A. SchÄfer, F.R.S., Text-book on Physiology, vol. i., p. 312.

31 The unorganised ferments are frequently otherwise classified than as above, not according to the locality, but according to the function. The chief are these:—amylolytic, those which change starch and glycogen (amyloses) into sugars, e. g., ptyalin, diastase, amylopsin; proteolytic, those which change proteids into proteosis and peptones, e. g., trypsin, pepsin; inversive, those which change maltose, sucrose, and lactose into glucose, e. g., invertin; coagulative, those which change soluble proteids into insoluble, e. g., rennet; steatolytic, those which split up fats into fatty acids and glycerine, e. g., steapsin.

32 A chemical change obtained by the action of sulphuric or some other acid, or by the influence of diastase.

33 Bacteriology and Infective Diseases, Appendix.

34 E. C. Hansen, Studies in Fermentation (Copenhagen), p. 98.

35 Proc. Royal Soc. of Edin., xxxvii., pt. iv., p. 759.

36 E. A. SchÄfer, Text-book of Physiology, vol. i., p. 25 (W. D. Halliburton).

37 "Denitrifying" means reducing nitrates.

38 R. Warington, M.A., F.R.S., Journ. Roy. Agricultural Soc. Eng., series iii., vol. viii., pt. iv., pp. 577 et seq.

39 The saltpetre beds of Chili and Peru are an excellent example of the industrial application of these facts. Nitrates are there produced from the fÆcal evacuations of sea-fowl in such quantities as to form an article of commerce. A like form of utilisation of the action of these bacteria was once practiced on the continent of Europe. Economic application is also seen in the treatment of sewage referred to elsewhere.

40 The course of nitrification may be followed by means of chemical tests. 1. The disappearance of ammonia. 2. The appearance of nitrite. 3. Its disappearance. 4. Appearance of nitrate.

41 Professor Warington, in Report IV. (p. 526) of his admirable series of papers on the subject, draws attention to MÜntz's criticism that the nitrifying organisms only oxidise from nitrogenous matter to nitrites, and not from nitrites to nitrates. MÜntz held that the conversion of nitrite into nitrate is brought about by the joint action of carbonic acid and oxygen. Professor Warington's experiments, however, clearly illustrate that the production of nitrates from nitrites in an ammoniacal solution can be determined by the character of the bacterial culture with which the solution is seeded, and that in a solution of potassium nitrite conversion into nitrate can be determined by the introduction of the nitric organism. Professor Warington still adheres to the opinion, in favour of which he has produced so much evidence, that the formation of nitrates in the soil is due to the nitric organism which soil always contains.

42 British Association for the Advancement of Science, Bristol, 1898, Presidential Address.

43 British Association for the Advancement of Science, Bristol, 1898, Presidential Address.

44 Sir John Lawes and Sir Henry Gilbert (Times, December 2, 1898), have pointed out that the addition of nitrates only would be of no permanent use to the wheat crop. They rely upon thorough tillage and proper rotation of crops as the means of improving the nitrogen value of the soil.

45 Geddes, Nature, xxv., 1882.

46 Sir Henry Gilbert, F.R.S., The Lawes Agricultural Trust Lectures, 1893, p. 129.

47 Ibid., p. 140.

48 This has been denied recently in the official report by the chemist of the Experimental Farm to the Minister of Agriculture at Ottawa (Report, 1896, p. 200).

49 It has already been pointed out that the nitrifying bacteria, though able to live on organic matter, do not require such either for existence or for the performance of their function.

50 Lehmann and Neumann, p. 305.

51 The conditions requisite for an outbreak of enteric fever were, according to Pettenkofer, (a) a rapid fall (after a rise) in the ground water, (b) pollution of the soil with animal impurities, (c) a certain earth temperature, and lastly (d) a specific micro-organism in the soil. These four conditions have not, particularly in England, always been fulfilled preparatory to an epidemic of typhoid. Yet the observations necessary for these deductions were a definite step in advance of mere dampness of soil.

52 Supplement to the Report of the Medical Officer of the Local Government Board, 1887, p. 7.

53 Report of Medical Officer to Local Government Board, 1895–1896, Appendix.

54 H. L. Russell, Dairy Bacteriology, p. 46.

55 Bureau of Animal Industry Reports, 1895–1896.

56 British Medical Journal, 1895, vol. ii., p. 322.

57 British Medical Journal, 1895, vol. ii., p. 322.

58 Journal of Comparative Pathology, vol. x. (1897), pp. 150–189.

59 E. W. Hope, M.D., D.Sc., Report of the Health of Liverpool during 1897, p. 40.

60 S. Rideal and A. G. R. Foulerton conclude, from a series of experiments, that boric acid (1–2,000) and formaldehyde (1–50,000) are effective preservatives for milk for a period of twenty-four hours, and that these quantities have no appreciable effect upon digestion or the digestibility of foods preserved by them (Public Health, May, 1899, pp. 554–568).

61 Report from Wisconsin Agricultural Experiment Station, 1896.

62 Jenner Institute of Preventive Medicine (First Series Transactions).

63 Centralblatt fÜr Bakteriologie, etc., II. Abteilung.

64 A Manual of Bacteriology, Clinical and Applied, p. 397.

65 Hewlett asserts that butter may contain from two to forty-seven millions of bacteria per gram.

66 Such pure cultures for such purposes are in the United States termed "starters," because they start the process of special ripening. For the sake of convenience the term will be used here.

67 The Essex County Council is one of the few public bodies in England which have undertaken pioneer work in this department of industry. Under the leadership of Mr. David Houston, a course of elementary instruction in dairy bacteriology as applied to modern dairy practice is given in the County Biological Laboratory at Chelmsford.

68 Report of Storr's Agricultural Experiments Station, State of Connecticut, 1895.

69 "Observations on Cheddar Cheese Making," Reports of Bath and West and Southern Counties Society, 1898, pp. 163–171. Mr. Lloyd's Reports to the West of England Society since 1892 contain various points respecting the application of bacteriology to cheese-making.

70 Journal of Bath and West of England Society, 1893, 1895, and 1897.

71 New York Medical Record, 1894.

72 British Medical Journal, 1896, ii., p. 760 et seq.

73 Special Report of the Medical Officer to the Local Government Board on Oyster Culture, etc., 1896.

74 Royal Commission on Tuberculosis, Report, 1895, pt. i., p. 13.

75 Ibid., p. 18.

76 British Medical Journal, 1895, vol. ii., p. 513.

77 It should be distinctly understood that this table is merely schematic and provisional. The details of toxin production and its effect are still open to revision and amendment.

78 Sidney Martin, M.D., F.R.S., F.R.C.P., Croonian Lectures delivered before the Royal College of Physicians, June, 1898.

79 It is impossible here to enter into a detailed consideration of the various views held with regard to the formation of antitoxins. It is needless to remark that the whole matter is one of abstruse technicality and intricacy. These antitoxic bodies gradually increase in the blood and tissues, and their action falls into two groups: (a) antitoxic, which counteract the effects of the poison itself; and (b) antimicrobic, which counteract the effects of the bacillus itself. "In one and the same animal the blood may contain a substance or substances which are both antitoxic and antimicrobic, such, for example, as occurs in the process of the formation of the diphtheria and tetanus antitoxic serums" (Sidney Martin).

80 Types of bodies possessing positive chemiotaxis for bacteria are the salts of potassium, peptone, glycerine.

81 Negative chemiotaxis is illustrated in alcohol, and free acids, and alkalies.

82 The friend of Addison and Pope, who married Mr. Edward Wortley Montagu in 1712, and on his appointment to the ambassadorship of the Porte in 1716 went with him to Constantinople. They remained abroad for two years, during which time Lady Wortley Montagu wrote her well-known Letters to her sister the Countess of Mar, Pope, and others.

83 Crookshank, History and Pathology of Vaccination.

84 An exhaustive account of vaccine may be found in the Milroy lectures delivered in 1898 at the Royal College of Physicians by S. Monckton Copeman, M.D.

85 Crookshank, Bacteriology and Infective Diseases; Virchow, The Huxley Lecture, 1898.

86 To shorten this period Dr. Cartwright Wood has adopted a plan by which time may be saved, and 200 cc. injected say within the first two or three weeks. This is accomplished by using a "serum toxin" (containing albumoses, but not ferments) previously to the broth toxin, an ingenious method which we cannot enter into here.

87 At the conclusion of the operation the cannula is removed from the jugular vein, and the wound is closed by the valvular character of the slit in the skin and vein and the elasticity of the wall of the vein. No stitching or dressing is required. Indeed, it is striking to observe in the horse an entire absence of pain throughout the proceedings.

88 The term unit is used as a standard measurement. This means the amount of antitoxin which will just neutralise ten times the minimum fatal dose of the toxin in a guinea-pig (250 grams toxin to kill on the fourth day). If 1 cc. of the antitoxic serum is required for this, one unit is contained in 1 cc.; if 0.01 cc. is sufficient, then 100 units are contained in the cc. Not less than 1500 units should be administered for a dose, and repeated every twelve hours. In severe cases two or three times this amount may be given.

89 The value of antitoxin treatment in diphtheria is discussed in the Brit. Med. Jour., 1899, pp. 197 and 268, by E. W. Goodall, M.D.

90 A detailed study of tuberculosis from its pathological and bacteriological aspect will be found in La Tuberculose et son Bacille, pt. i., Straus, Professeur À la FacultÉ de MÉdecine de Paris.

91 For differences of virulence between these conditions of pulmonary tubercle see Lingard, Local Government Board Report, 1888, p. 462.

92 Centralblatt. f. Bact. und Parasit., vol. vii., p. 9.

93 Animal Tuberculosis, p. 129.

94 See the Harben Lectures, November, 1898, by Sir Richard Thorne Thorne, Medical Officer to the Local Government Board; also the Report of the Royal Commission on Tuberculosis, 1896–98.

95 1. Tuberculosis is a disease mainly affecting the lungs (consumption, decline, phthisis) of young adults and the bowels of infants (tabes mesenterica). It may affect any part of the body, and its manifestations are very various. It also affects animals, particularly cattle, by whom it may be transmitted to man.

2. Its direct cause is a microscopic vegetable cell, known as the Bacillus tuberculosis, discovered by Koch in 1882. This fungus requires to be magnified some hundreds of times before it can even be seen. When it gains entrance to the weakened body it sets up the disease, which is an infectious disease, though different in degree to the infectiousness of, say, measles.

3. Trade influence and occupation, in some cases, undoubtedly predispose the individual to tubercle. Cramped attitudes, exposure to dampness or cold, ill ventilation, and exposure to inhalation of dust of various kinds, all act in this way. In support of the evil effect of each of these four conditions much evidence could he produced.

4. Overcrowding has a definite influence in propagating tubercular diseases. The agricultural counties without big towns, like Worcestershire, Herefordshire, Buckinghamshire, and Rutland, are the counties having the lowest mortality from tuberculosis; whilst the crowded populations in Northumberland, South Wales, Lancashire, London, and the West Riding suffer most. Speaking more particularly, the overcrowded areas of London, such as St. Giles', Strand, Holborn, and Central London generally, show very high tubercular death-rates.

5. Tuberculosis is not increasing. During the last thirty years it has shown, with few exceptions, a steady decline in all parts of England. "Consumption" is most fatal in comparatively young people (fifteen to forty-five years), whilst "tabes" and other forms of tubercle are fatal chiefly to young children. These forms have not declined so much as the lung form. The mortality in consumption of males has since 1866 been in excess of that of females. The age of maximum fatality from consumption is later than in the past, which is probably due to improved hygiene and treatment.

6. This decline has been due, not to any special repressive measures—for few or none have been carried out—but to a general and extensive social improvement in the life of the people, to an increase of knowledge respecting tuberculosis and hygiene, to an enormous advance in sanitation, and to more efficient land drainage.

7. Not all persons are equally liable to consumption, some being much more susceptible than others. We have mentioned the predisposing influence of certain trades. There is also heredity, which acts, as we have said, in transmitting a tubercular tendency, not commonly the actual virus of the disease; there is, thirdly, the debilitating effect of previous illness or chronic alcoholism; there is, fourthly, the habitual breathing of rebreathed air; and, fifthly, there are the conditions of the environment, like dampness and darkness of the dwelling. Such influences as these weaken the resisting power of the tissues, and thus afford a suitable nidus for the bacillus conveyed in milk or by the inspiration of infected dust.

8. Consumption is curable if taken in time. In cases where the lungs are half gone, and consist of large cavities, it is obvious that curability is out of the question. But if the disease can be properly treated in its earliest stages, there is considerable likelihood of recovery.

9. The breath is not dangerous, as far as we know, but there is danger from discharges of any kind from any infected part, whether lungs or bowels; for such discharges, when dry, may readily pollute the air, and either the bacilli or spores be inhaled into the lungs.

10. The chief channels of personal infection or the spread of the disease amongst a community are two: (a) dried tubercular sputum (or other tubercular discharges); (b) infected milk or meat. So long as the former remains wet or moist, infection cannot take place. It is, of course, better to destroy it completely. As for milk and meat, boiling the former and thoroughly cooking the latter will remove all danger.

11. The expectoration is infective. This is one of the commonest modes of infection, and to it is held to be due the large amount of respiratory tuberculosis (consumption, phthisis). The expectoration from the lungs must contain, from the nature of the case, a very large number of bacilli. As a matter of fact, a single consumptive individual can cough up in a day millions of tubercle bacilli. When expectoration becomes dry, the least current of air will disseminate the infective dust, which can by that means be readily reinspired. Expectoration on pavements and floors, as well as on handkerchiefs, may thus become, on drying, a source of great danger to others. The discharges from the bowels of infants suffering from the disease also contain the infective material.

12. Milk, though a much more likely channel for conveyance of tubercle than meat, is only or chiefly virulent when the udder is the seat of tuberculous lesions. The consumption of such milk is only dangerous when it contains a great number of bacilli and is ingested in considerable quantity. Practically the danger from using raw milk exists only for those persons who use it as their sole or principal food, e. g., young children. All danger is avoided by boiling or pasteurising the milk.

At the same time there is an increasing amount of evidence forthcoming at the present time which goes to prove that milk is not infrequently tainted with tubercle (see p. 195). The tuberculin test should be applied to all milch cows, and the infected ones isolated from the herd. Milk supplies should be more strictly inspected even than cowsheds.

13. There are several methods by which meat infection can be prevented. In the first place, herds should be kept healthy, and tubercular animals isolated. Cowsheds and byres should be under sanitary supervision, especially as regards overcrowding, dampness, lack of light, and uncleanliness. Public slaughter-houses under a sanitary authority would undoubtedly be most advantageous. Meat inspection should also be more strictly attended to; efficient cooking, and avoidance of "roll" meat which has not been thoroughly cooked in the middle.

14. Consumptive patients may diminish their disease. Dr. Arthur Ransome95a has laid down five axioms of hygiene for phthisical patients which, if followed, would materially improve the condition of such persons. At Davos, St. Moritz, Nordrach and other places where they have been practised, the beneficial change has been in many cases extraordinary:

(1) Abundance of light, nutritious, easily digested food, which must comprise a large allowance of fat; small meals, but frequent;

(2) An almost entirely open-air life, with as much sunshine as can be obtained;

(3) Suitable clothing, mostly wool;

(4) Cleanliness and bracing cold-water treatment;

(5) Mild but regular exercise.

15. Consumptive patients may also assist in preventing the spread of the disease. In the first place, they should follow the hygienic directions just mentioned, because such conditions fulfilled will materially lessen the contagiousness of such patients; next, the expectoration must never be allowed to get dry. A spitting-cup containing a little disinfectant solution (one teaspoonful of strong carbolic acid to two tablespoonfuls of water) should always be used, or the expectoration received into paper handkerchiefs which can be burnt. Spoons, forks, cups, and all such articles should be thoroughly cleaned before being used by other persons. The patient should not sleep in company with another, but occupy, if possible, a separate bedroom.

Isolation hospitals for consumptives, as for patients suffering from diphtheria, are now being established.

16. House influence has some effect, both directly and indirectly, upon tubercular diseases. Damp soils, darkness, and small cubic space in the dwelling-house exert a very prejudicial effect upon tubercular patients. Sir Richard Thorne[95b] has described the favourable house for such persons as one built upon a soil which is dry naturally or freed by artificial means from the injurious influences of dampness and of the oscillations of the underlying subsoil. The house itself should be so constructed as to be protected against dampness of site, foundations, and walls. Upon at least two opposite sides of the dwelling-house there should be enough open space to secure ample movement of air about it, and free exposure to sunlight. Lastly, it should be possible to have free movement of air by day and night through all habitable rooms of the house. It is clear that many inhabited houses could not stand to these tests; but effort should be made to approach as near to such a standard as possible.

17. Sunlight and fresh air are the greatest enemies to infection.

18. Disinfection is necessary after death from phthisis, and should be as complete as after any other infective disease. Compulsory notification of fatal cases and compulsory disinfection have been officially ordered by the Prussian Government. In this country also absolute disinfection should always be insisted upon after phthisis. Walls, floors, carpets, curtains, etc., should be strictly sterilised. Professor DelÉpine recommends spraying with 1–100 solution of chloride of lime.

[95a] Arthur Ransome, M.D., F.R.S., Treatment of Phthisis.

[95b] Practitioner, vol. xlvi.

96 Journal of State Medicine, vol. iv. (1896), p. 169.

97 For a fuller statement see Trans. Jenner Institute (First Series), pp. 7–32.