It is well known that the air of wells, mines, &c. is sometimes capable of extinguishing a flame, and recent researches have shown that this is almost always due to deficiency of oxygen, accompanied by the presence of a considerable percentage of CO21. The extinctive atmosphere is popularly known as “choke-damp” or “black-damp.” The source of the CO2 is not necessarily the same in all cases. If oxidisable organic matter is present it is reasonable to suppose that the CO2 may be derived from the carbon in this organic matter by the action on it of air; but the derivation remains a supposition. Carbonaceous materials may be oxidised and yet give no CO2. The other obvious source of CO2 is the decomposition of carbonates by an acid, the acid being produced by some process of oxidation. The commonest mineral which will yield an acid by oxidation with air is pyrites, and if direct oxidation of carbonaceous matter be ruled out, it may be assumed that the occurrence of CO2 is ultimately referable to pyrites in an easily oxidisable form, for example as marcasite.

In the preceding paper we have put forward the result of some experiments in which B. pestis was passed through a series of 26 rats by means of the subcutaneous method and without the intervention of any culture on artificial media. From this series of experiments it appeared that the virulence of the organism was not affected by passage through the ordinary rats of Bombay.

During my bacteriological investigations on the enlarged prostate gland which I am carrying out in conjunction with Mr Cuthbert Wallace, I have isolated a bacillus which presents the following characteristics and which appears to be, so far as I can ascertain, an organism which has not previously been met with.

We have previously referred to the fact that a certain number of Bombay rats were immune both to subcutaneous and to cutaneous inoculations of virulent plague bacilli. In paper V, p. 505 above, we were able to record that 59% of rats in Bombay could withstand the rubbing on scarified surfaces of emulsions of spleens of rats which had died of acute plague. The fact that a large number of rats in India, where plague had occurred, were more or less immune has been noted by Simond and Walton.

Since the publication of the Indian Plague Commission in 1901, with the exception of a short paper by Hankin (1905), comparatively little has been published in scientific journals dealing with the spread of plague in India from an epidemiological view-point. Not that this has been lost sight of in India, for there are many very valuable reports in existence in the archives of the various local Governments, containing most interesting observations made by officers of the Indian Medical Service who have dealt personally with the epidemics; but as these reports are, in the nature of things, not available for reference by the public, it has been thought advisable and useful to compile a digest of them for publication.

H. Smidt in a recent note on the reduction of methylene blue by means of milk confirmed the results of Schardinger that a mixture of formaldehyde and methylene blue is decolorised by the action of milk. This reaction depends on the presence of a ferment—a catalase—in the milk, and, as this ferment is readily destroyed by heat, serves as a very simple method of determining whether a given sample of milk is “raw” or not. By way of conclusion Smidt stated that he thought this test might be of still further utility in that it might be possible to estimate the degree of bacterial contamination of the milk by its means. If such a comparatively simple test could be employed, in an easy and effective fashion, it would be of immense service, as, owing to the rapidity with which it can be carried out, the milk could be examined before distribution.

From these two series of experiments we can conclude that a cowdung floor, grossly contaminated with a virulent culture of B. pestis, can retain its infectivity for 48 hours but not longer, and that a chunam floor, treated in the same way, does not remain infective even for 24 hours.

Phthisis (pulmonary tuberculosis) is distinguished from nearly all other infectious diseases by its protracted duration and by the prolonged disability which it imposes upon enormous numbers of the total working population. It is further distinguished by the complexity of the influences which are regarded as affecting its spread or capable of controlling its prevalence. It is therefore of the first importance that the relative values of measures for controlling phthisis should be closely studied, and that special attention should be given to those which promise the greatest yield for a given expenditure. In particular it is important to be aware of any which can be set to work without the delay and expense involved in creating a new service. The present paper is intended as a contribution to this study. The facts collected in it and others of a similar kind deserve more extended investigation than it has been possible for me to give them in the intervals of official work. They are put forward here without any illusions as to the inevitable shortcomings of their presentation but with a conviction that from the economic standpoint they are of fundamental importance in the prevention of phthisis.

In 1898 Arloing and Courmont published the results of experiments made by them on the agglutination produced by the serum of tubercular patients. For this purpose they used a strain of the tubercle bacillus isolated by the former, which produced a uniform turbidity when grown in glycerine broth. With this culture, serum from tubercular patients gave reactions at dilutions of 1 in 5, 10 or 20 in a large percentage of cases, and that from normal individuals only in a much smaller percentage and then not very strongly. From this they concluded that the agglutination reaction was likely to be of considerable use in the diagnosis of tuberculosis.

With ordinary care and cleanliness it is possible to obtain milk which, when freshly drawn, contains less than 1500 organisms per cubic centimetre.

Freshly drawn milk should not contain gas-forming organisms in at least 50 c.c.

Gas-forming organisms are present in milk owing to contamination with faecal material. Of these organisms the B. oxytocus perniciosus, the B. neapolitanus and the B. coli communis occur in greatest number in fresh milk, while the B. cloacae and B. lactis aerogenes appear at a later stage.

Out of 107 non-chromogenic lactose fermenters isolated from milk only one bacillus gave the reactions of the B. acidi lactici (Hüppe); while the B. Grünthal, B. pneumoniae (Friedländer), and the B. coscoroba have not been met with once.

Finally, I desire to enter a plea for the substitution of certain fermentation reactions in the place of some of the tests now usually employed, in the routine examination of water and food-stuffs, to identify these organisms. At present bacteriologists make use of some, or all, of the following tests:

1. Morphology.

2. Motility.

3. Staining by Gram's method.

4. Character of the growth on nutrient gelatin.

5. Liquefaction of gelatin.

6. Action on milk.

7. Foemation of indol.

8. Fermentation of glucose.

9. Fermentation of lactose.

10. Fermentation of cane sugar.

11. Action on neutral-red.

All the organisms mentioned in Tables I and II produced clotting in milk, fermented glucose, gave the neutral-red reaction, had much the same morphology, and the growths on agar and gelatin did not afford any assistance towards differentaniting between them.

I would therefore suggest that instead of five of the tests, Nos. 4, 6, 7, 8, and 11, we should substitute the following:

Fermentation of dulcit,

Fermentation of adonit,

Fermentation of inulin,

Vodes and Proskauer's reaction, as by so doing we should get a finer differentiation without increase in work and we should not be classing as B. coli organisms which may have little in common with, and have a distribution entirely different from that of the B. coli communis.

The blood of plague-infected rats may contain an enormous number of plague bacilli, even as many as 100,000,000 per c.c. having been found before death. On the other hand rats occasionally die from plague with little or no septicaemia. An insect sucking the blood of most rats shortly before death would imbibe a large number of bacilli.

While the blood of a rat may have as many as 100,000,000 organisms in a c.c. the urine may have none at all, or at least less than 10 per c.c. Plague bacilli were discovered in the urine in 29 per cent. of the cases. When the urine does contain plague bacilli they are always present in much fewer numbers than in the blood.

The faeces of rats dead of plague and the blood of which contained abundant bacteria are not highly infective and would appear to play little part in the spreading of the epizootic.

The “graphic” method of constructing a Life-Table which is ably and lucidly expounded in the paper by Drs Newsholme and Stevenson (published in the Journal of Hygiene, vol. III. No. 3, pp. 297—324), is one way of dividing up foundation figures of population and deaths, given in groups of ages, into numbers belonging to each separate year of age, so that, either directly by the fraction , or indirectly by first obtaining , and then finding the value of , the series of px values is obtained forming the connecting link between the data and the results of the Life-Table.

An investigation of the blood of 28 patients suffering from plague has been made, involving the examination of 74 specimens. The B. pestis was not found in the blood of five patients whose illness ended in recovery; nor was it found in seven of the fatal cases. The salient facts ascertained from an analysis of the remaining 16 fatal septicaemic cases may be recapitulated thus:

(1) Microscopical examination of the blood cannot be regarded as a trustworthy criterion of the degree septicaemia.

(2) A severe septicaemia may be present at a comparatively early stage of the disease and for a considerable number of hours before death.

(3) The septicaemia may be of an irregular or fluctuating type.

The use of earthenware as a filtering material for the purification of water is probably of very ancient origin, but the modern modification, the porcelain filter, according to Gautier (1890), is due to Nadaud de Buffon (1861). Earthenware filters in general serve the useful purpose of aërating the water and retaining suspended matter and are therefore valuable in rendering boiled and rain water clear and palatable. The first application of bacteriological methods of examination by pupils of Robert Koch showed, however, that the great majority of these and other water filters gave no protection against disease organisms. Hesse (1885–6) found that clays and asbestos retained micro-organisms to a marked extent, and, although Plagge (1886) confirmed this observation he demonstrated that but few filters prevented the direct transmission of bacteria and that even the best after a few days contaminated the filtrates indirectly. This indirect contamination Plagge attributed to the growth of micro-organisms within the filter mass and so pronounced is its influence that porcelain filters after being a few days in action give filtrates richer in germs than the original water. Schäfer (1893) states that porcelain filters do not allow organisms to grow through them when the water filtered is of such a character that the organisms cannot multiply in it. He points out that the waters usually filtered for domestic purposes do not allow B. typhosus and V. cholerae to grow, and that in such cases porcelain filters are efficient. Unfortunately, however, drinking waters do occur in which these organisms can multiply, and then indirect contamination is inevitable if the filter be allowed to act more than a few days without sterilisation.

(1) It is a matter of considerable interest that, with the exception of rat No. 1832, the rats were caught alive during a period when no rats with acute plague were found and when no human cases were occurring in the locality.

(2) It cannot be regarded merely as a coincidence that the lesions were in every instance situated within the abdomen. With our present knowledge it would be rash to speculate as to the method of infection in these cases, but it may be conceded that the most reasonable interpretation of the lesions involves the assumption of an intestinal infection.

(3) Examination after the animals were killed furnished no indication that their health suffered in any way; the organs were apparently normal and there was no emaciation.

(4) Although the number of cases is admittedly small and although it is difficult to estimate virulence with any degree of accuracy, yet it is noteworthy that of the animals inoculated directly from, and with subcultures of, these abscesses only one survived.