Fleas that have fed on septicaemic blood are capable of conveying infection to fresh animals on which they feed. This capability is associated with the presence of plague bacilli in the stomach, intestine and faeces.

Henle (1889) found that “Creolin”, an emulsion of tar acids, was a more efficient disinfectant than could be explained from observations upon each of its constituents separately, and concluded that the extra efficiency was connected with the emulsified form. Henle's conclusions do not appear to us to be necessarily justified by his observations.

1. The time in which an animal or man exposed to compressed air becomes saturated with nitrogen varies in different parts of the body from a few minutes to several hours. The progress of saturation follows in general the line of a logarithmic curve and is approximately complete in about five hours in man and in a goat in about three hours.

2. The curve of desaturation after decompression is the same as that of saturation, provided no bubbles have formed.

3. Those parts of the body which saturate and desaturate slowly are of great importance in reference to the production of symptoms after decompression.

4. No symptoms are produced by rapid decompression from an excess pressure of 15 pounds, or a little more, to atmospheric pressure, i.e. from two atmospheres absolute to one. In the same way it is safe to quickly reduce the absolute pressure to one-half in any part of the pressure scale up to at least about seven atmospheres: e.g. from six atmospheres (75 pounds in excess) to three (30 pounds), or from four atmospheres to two.

5. Decompression is not safe if the pressure of nitrogen inside the body becomes much more than twice that of the atmospheric nitrogen.

6. In decompressing men or animals from high pressures the first part should consist in rapidly halving the absolute pressure: subsequently the rate of decompression must become slower and slower, so that the nitrogen pressure in no part of the body ever become more than about twice that of the air. A safe rate of decompression can be calculated with considerable accuracy.

7. Uniform decompression has to be extremely slow to attain the same results. It fails because it increases the duration of exposure to high pressure (a great disadvantage in diving work), and makes no use of the possibility of using a considerable difference in the partial pressure of nitrogen within and without the body to hasten the desaturation of the tissues. It is needlessly slow at the beginning and usually dangerously quick near the end.

8. Decompression of men fully saturated at very high pressures must in any case be of very long duration: and to avoid these long decompressions the time of exposure to such pressures must be strictly limited. Tables are given indicating the appropriate mode and duration of decompression after various periods of exposure at pressures up to 90 pounds in excess of atmospheric pressure.

9. Numerous experiments on goats and men are detailed in proof of these principles.

10. The susceptibility of different animals to compressed-air illness increases in general with their size owing to the corresponding diminution in their rates of circulation.

11. The average respiratory exchange of goats is about two-thirds more than that of man; they produce about 0·8 gram. of CO2 per hour per kilogramme of body weight.

12. The mass of the blood in goats is six and a half or seven and a half per cent. of the “clean” body weight.

13. The individual variation among goats in their susceptibility to caisson disease is very large. There is no evidence that this depends directly on sex, size or blood-volume: there is some evidence that fatness and activity of respiratory exchange are important factors.

14. Death is nearly always due to pulmonary air-embolism, and paralysis to blockage of vessels in the spinal cord by air. The cause of “bends” remains undetermined; there are reasons for supposing that in at least many cases they are due to bubbles in the synovial fluid of the joints.

15. In our experiments bubbles were found post-mortem most freely in the blood, fat and synovial fluid; they were not uncommon in the substance of the spinal cord, but otherwise were very rarely found in the solid tissues.

(1) A localised epidemic of diphtheria of a clinically mild type (both as regards local and general symptoms) was associated with the prevalence in the fauces of patients and contacts of strains of B. diphtheriae of low pathogenicity for animals; 35% of these strains possessed moderate virulence for guinea-pigs, 30% low virulence and 35% were non-virulent.

(2) Prolonged nasal discharge after moderately severe diphtheria was in one case associated with a strain of B. diphtheriae which was non-virulent for guinea-pigs.

(3) Acid production in various carbohydrate media proved a valuable means of differentiating diphtheria-like bacilli, but the exact composition of the medium is of importance. Peptone water appears to be especially suitable for the basis as being least liable to variation.

(4) The agglutination test gave a fairly uniform result with most of the strains of virulent B. diphtheriae, but three virulent strains did not give a decided positive reaction to this test. Of the non-virulent strains half gave a slight, the remainder a negative result.

Bacillus pseudo-diphtheriae (Hofmann) and certain acid producing diphtheroids gave no reaction.

(5) B. fusiformis and spirochaetes occurred in large numbers on the fauces in this epidemic of diphtheria, in association with the B. diphtheriae.

(6) After all the boys had received prophylactic infections of antitoxin and after the carriers had been isolated the epidemic promptly ceased.

I have to thank Lieut.-Col. Sir Joseph Fayrer, Medical Officer of the Duke of York's School, who was at the time Acting Commandant, for his permission to publish this account.

I am very much indebted to Dr Boycott and Dr Marshall for the very large amount of help which they gave me, and to Dr Dean for his assistance throughout the investigation.

Hitherto all efforts to set up immunity against vaccinia in animals have been restricted to the vaccination of animals in the customary manner, or to the injection of vaccine lymph into them.

1. Temperature influences the rate at which glycerinated lymph deteriorates in accordance with the law of Arrhenius, expressing the effect of temperature upon chemical action; the rate of deterioration increasing three times per 10° rise in temperature.

2. Dry powdered calf vaccine in sealed glass capillary tubes still gave rise to typical vesicles after exposure to a temperature of 100°C. for from 5 to 10 minutes.

3. The vaccine virus can withstand positive osmosis for 24 hours or more, and negative osmosis for 8 weeks or more, at room temperature.

4. It appears doubtful whether the vaccine virus will pass through a Berkefeld V filter even when a stored vaccine emulsion is used for filtration. If any virus does pass through it only does so exceptionally and in small quantities.

5. When a glycerinated vaccine emulsion is filtered, white flocculi frequently form in the filtrate. These are at first minute, but subsequently adhere and form a macroscopic sediment. This sediment, when inoculated on calves, does not cause vesiculation.

Microscopically these flocculi, in hanging drop preparations, resemble the vaccine bodies described by one or more observers.

1. Both in Bombay city and in the Amritsar district of the Punjab there is a distinct seasonal variation in the number of rat fleas.

2. In these places this seasonal variation of rat fleas corresponds directly in a general way with the plague mortality. During the season when plague is epidemic the average number of fleas per rat is above the mean, while during the non-epidemic season it is below the mean. The height of the epidemic corresponds fairly closely with the season of maximum flea prevalence.

In a previous communication (1906) it was shown by Bulloch and Craw that the Doulton “white filter” prevented the direct transimmission of micro-organisms, and that the filtrates from highly contaminated waters were germ free until sufficient time had been given for the bacteria to grow through the filter mass. It was demonstrated, in fact, that the Doulton filter was at least as efficient in the retention of micro-organisms as the best material on the market, viz. the Pasteur-Chamberland filter, and excelled the latter in its rate of filtration. It was pointed out that, with the possible exception of Kieselguhr, filters, only porcelain bougies could be relied upon to prevent direct transmission of germs. During the past year we have tested the relative efficiency of porcelain and Kieselguhr filters, in particular the Doulton porcelain filter and the Berkefeld Kieselguhr filter. A few samples of the Slack and Brownlow filter (sand and porcelain mixture?) were also tested.

In a recent paper by Miss Chick on “The Laws of Disinfection”, it was pointed out that disinfection of bacteria is strictly analogous to a chemical reaction in which individual bacteria play the part of molecules. Thus, if n be the number of bacteria present at any time t during dis-infection, , where K is a constant. Also, if K1, K2 are these constants for two different temperatures is also constant, i.e. Arrhenius' formula for the temperature coefficient of chemical reactions holds good in the case of bacteria as well. In addition to this, it was found that the relation between the concentration of the disinfectant and the time of disinfection (that is, the time required to reduce the original number of bacteria by a given percentage) might abe approximately expressed by the empirical law

where C is the concentration at time t.

We have no desire to claim for the tests described above that they will be found applicable to every strain of organism belonging to any particular group. Our experiments were necesarily limited to a few races of each—many of these being probably avirulent from long subcultivation on artificial media. We merely wish to indicate the general methods we would adopt in any case of difficult bacteriological diagnosis, although as a matter of fact the only tests we found it necessary to use in the course of our work were the method of cutaneous and subcutaneous inoculation into animals and the stalactite test.

The tests referred to in this paper may be summarised thus:

1. The plague bacillus gives a fairly characteristic type of colony on neutral agar; it forms typical stalactites in neutral broth; it gives certain definite fermentation reactions.

2. B. pseudotuberculosis resembles B. pestis more closely than any other organism. The animal test on white rats is probably the best for its differentiation.

3. Bacilli of the haemorrhagic septicaemia group appear to be inhibited in their growth in media containing sodium taurocholate.

4. Bacilli of the B. enteritidis (Gaertner) group are the most readily distinguished of all; the appearance of agar cultures, the negative stalactite test, and their fairly definite fermentation sugar reactions are sufficient to mark them off from the plague bacillus.

Plagge in 1886 observed that but few water filters prevented the direct transmission of micro-organisms and that all gave contaminated filtrates after being a few days in operation. This result has been widely confirmed, especially by Woodhead and Wood (1894, 1898), and by Bulloch and Craw (1906). Plagge considered that in the case of those filters which did not permit of the immediate or direct transmission of germs the subsequent failure of the filters was due to the gradual growth of the organisms through the filter mass, a view which has been adopted by v. Esmarch (1902) and is generally accepted.

1. The trypanosome of the gold-fish has been successfully cultivated on the medium of McNeal and Novy.

2. Preparatory to division in culture, the original trypanosome as found in the blood of the fish assumes a somewhat tadpole-like appearance, the endoplasm and its contained structures being collected together in the swollen posterior end. The kineto-nucleus now lies close to, and alongside of, the tropho-uncleus, and the latter has become swollen and loose in structure with its chromatin broken up into chromidia. The anterior third or more of the trypano-some undergoes little or no change in form and does not take part in division. It is thus easily seen how the product of the preliminary division comes to have a Crithidia-like appearance.

3. The product of this preliminary division—Crithidia-like by the relative position of kineto-and tropho-nuclei—is capable of freely multiplying.

According to Brumpt it is in the Crithidia-like form that free multiplication of the eel trypanosome first takes place in the stomach of Hemiclepsis. It may well be that in this case also the Crithidia-like form is arrived at by steps such as are here figured and described.

4. Crithidia-like forms are found at all stages of the culture and along with them at various stages other forms where the body is elongated and the kineto-nucleus still close to the tropho-nucleus, and yet other forms where the kineto-nucleus until true trypanosome-like forms are reached.

5. These trypanosome-like forms (resembling mammalian trypanosomes rather than those of the fish from which they are derived) are most numerous in the later stages of the culture.

Whilst the studies of A. C. Houston and MacConkey have extended our knowledge of the characters of the bacilli found in faeces, and those of Dudgeon and Sargent have done the same with regard to colon bacilli met with in cases of appendicitis, the fermentative activities of pathogenic colon bacilli occurring in urine have not been investigated to any great extent.