In this Journal (vol. VII. p. 501) Mr J. A. Craw has recently published a very sharp criticism of my calculations based on experiments by Madsen and Walbum regarding the so-called Danysz Effect.

The phenomenon of supersensitization observed on repeated injection of alien sera has lately aroused much experimental and clinical interest. The following cases which led me some three years ago, on clinical grounds to assume the occurrence of this phenomenon, appear worth recording, especially since the reaction happened not with anti-diptheritic or anti-plague but with anti-tuberculous serum.

1. Many horses immunised against other bacteria or bacterial products will give a large local reaction to mallein, but this is usually not associated with a rise in temperature. In the case of horses injected with diphtheria toxin, the size of the swelling appears to related to the degree of immunity attained. This point has not yet been established in the case of horses immunised against other bacterial products.

2. This local reaction disappears rapidly and can thus be distinguished from the reaction in the case of glandered horses.

3. In the few cases when a rise in temperature took place (3 cases out of 56) the curve was markedly different from that obtained in the case of glandered animals.

4. Other bacterial products react similarly to mallein upon immune horses.

1. The typhoid bacillus can survive in natural soil in large numbers for about 20 days and is still present in a living condition after 70 to 80 days.

2. There is no evidence that the typhoid bacillus is capable of multiplying and leading a saprophytic existence in ordinary soil.

3. In some samples of soil, but not in all, the typhoid bacillus dies out much more rapidly (in 11 days) if the soil has previously been subjected to sterilisation by steam under pressure. This is apparently due to the production of bactericidal substances during sterilisation.

(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.

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.

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.

1. The phenol solutions used as a standard in the bacteriological testing of disinfectants should be made from pure freshly distilled phenol.

2. The actual quantity of phenol, cresylic acid and water present in commercial carbolic acids and in carbolic powders may be estimated by extracting the oils and testing their germicidal power.

3. The comparative germicidal value of disinfectant powders may be estimated by keeping the powder and organism in contact by mechanical means during the whole period of the experiment.

1. A very complete analogy exists between a chemical reaction and the process of disinfection, one reagent being represented by the disinfectant, and the second by the protoplasm of the bacterium.

2. Three classes of disinfectants were studied, (a) metallic salts (HgCl2 and AgNO3), (b) phenol, and (c) emulsified disinfectants (disinfectant “A”). B. paratyphosus and spores of B. anthracis were chosen as types of vegetative and spore-bearing organisms respectively.

3. In the case of anthrax spores, the disinfection process proceeds in obedience to the well-known equation for a unimolecular reaction, if numbers expressing “concentration of reacting substance” are replaced by “numbers of surviving bacteria”.

4. Experiments with B. paratyphosus show a departure from the simple law owing to permanent differences in resistance to disinfectants among the individual organisms. The younger bacteria were proved to be the more resistant.

5. The process of disinfection is influenced by temperature in an orderly manner, and the well-known equation of Arrhenius can be applied.

(a) Disinfection of B. paratyphosus by metallic salts is influenced by temperature to about the same degree as most chemical reactions, the reaction velocity being increased about three-fold for a rise in temperature of 10°C.

(b) For disinfection of B. paratyphosus by phenol and the disinfectant “A” there was a much higher temperature coefficient, viz., seven to eight. In the case of phenol the effect of temperature was again found to be complicated by the want of uniformity among the individual bacteria. Disinfection of the younger, more resistant bacteria, was found to possess a higher temperature coefficient than that of the less resistant forms, the coefficient varying from ten to three, or two according to the age and number of the bacteria disinfected.

6. It follows from (5) that there is a very great advantage in the use of warm solutions for practical disinfection.

7. Experiments, made with varying concentrations of disinfectant, and using similar groups of bacteria from cultures of B. paratyphosus, showed a definite logarithmic relation, between the concentration of disinfectant and the mean reaction velocity of disinfection, to exist in the case of phenol and the disinfectant “A”.

8. In the case of silver nitrate, the same relation existed, but, in the case of mercuric chloride, numbers representing concentration of the salt had to be replaced by those representing concentration of the metallic ion. This confirms the theory that in disinfection with metallic salts the metallic ion is the real disinfecting agent.

9. This logarithmic relation is surprising in view of the simple proportionality existing in the case of chemical processes running the course of a unimolecular reaction, with which disinfection shows a close analogy.

10. Some evidence was obtained that, in disinfection with mercuric chloride, a toxic compound is formed between the metal and the substance of the bacterial cell. This compound prevents all further growth, but vitality can be restored by the administration of a large excess of soluble sulphide as an antidote.

I am glad to have this opportunity of expressing my great indebtedness to Dr C. J. Martin, at whose suggestion the work was undertaken, and who has helped me throughout, not only with most valuable advice, but also with practical assistance in many of the experiments.