In a former communication (1) we showed that a substance acting as complement is present in milk under both normal and abnormal conditions, and that this substance displays characteristics which lend a certain amount of doubt as to its true complementary nature. Expression was also given to the idea, that the haemolytic system—heated ox-serum + guinea-pig corpuscles—is of a peculiarly sensitive character in regard to ox-complement in the presence of milk.

This subject was first considered statistically by the late Dr Farr. It is one of the brilliant attempts to extract the real meaning of figures so frequent in his work, but though this theory has not shared in the complete neglect that has been the lot of his attempt to put a quantitative measure to the course of epidemics, it has suffered as much from the kind of patronage with which it is usually discussed. On at least one of the great medical officers of health of his time, however,— the late Dr J. B. Russell—the theory exercised a strong fascination. My own copy of Fare's Vital Statistics came from Dr Russell's library, and the whole passage referring to the law is lined with his characteristic nervous pencil marks, while in much of his work on vital statistics the influence can easily be traced.

This is a particularly difficult branch of the subject to investigate. It might be thought at first sight that the death rates at different age periods might be compared, and this is often done; but when it is noted that the death rates at different age periods are organically connected, it is obvious that such a comparison is statistical or actuarial and completely neglects the biology of the subject. To illustrate the problem a diagram is given. This is constructed on a principle open to objection, but, if that is remembered, it illustrates a number of points. The healthy district life table H2 has been taken as a standard of comparison. Now a healthy district life table labours under certain disadvantages. A district may, as the Register General says, be excluded because it contains an institution drawing its inmates from a wider district. This is not a serious objection. A more serious objection is the fact that whether deaths which might be considered to belong to the district are returned to it or not, the result is equally unsatisfactory. Everyone who has had practical experience knows many instances in which it is impossible to allocate a death to the district to which it properly belongs. When all is balanced, I think that probably on the whole the healthy districts get credit for more than their share of deaths, that is, for more deaths than would occur if there was no process of intermingling of town and country. For one death the town gets credit for, the country gets credit for another, in the one case some old person dying of a cancer in a hospital, in the other, some poor young person, who having tried city life, returns broken, to die of phthisis or some similar disease. Thus a healthy district life table is open to objection as a criterion. It is, however, for the purpose at present required, the only one at our disposal.

In recent years it has been found that in vitro many ferments, etc., lose their power of action at a rate corresponding to the monomolecular reaction, i.e. if the amount of the substance present at the beginning is denoted by unity, and, if after a certain period of time only one half of the substance remains active, then it may be predicted that at the end of an equal period of time, one half of one half, or only one quarter of the original amount, will still retain its power of a.ction. It is not necessary to give examples, they are sufficiently well known.

In a large number of cases the curves which describe the rate at which ferments, antibodies, etc., disappear in the body accord in form with the equations of physical chemistry, but not so as to be readily interpretable. If one molecule, two molecules, etc., take part in a reaction then it is clear that the indices in the equations must bear certain relations to whole numbers. Failure to conform to these relations seems at first sight to imply that a fraction of a molecule takes part in a reaction, but this is not necessarily the case. Such a failure has been found to appear when the curves of many vital phenomena, e.g. the disappearance of agglutins in an organism, are fitted to physico-chemical equations. A possible meaning, however, can easily be seen.

1. A fresh emulsion of tubercle bacilli in salt solution when used as the antigen will give about 90 % of positive results in cases of pulmonary tuberculosis, whilst in healthy persons the result is negative.

2. In cases suspected of pulmonary tuberculosis, the results of this test conform closely to those given by a combination of the opsonic index test with injections of tuberculin, and so may be of value in diagnosis.

3. Diseases other than tuberculosis have always been negative, but only a small number of such cases have been examined.

4. An emulsion of tubercle bacilli when used as an antigen must be freshly prepared immediately before use, and should be made from a young subculture.

5. Owing to the differences in complements, they should always be titrated in the presence of the antigen, and probably also in the presence of both antigen and normal serum.

6. Exercise does not seem to affect the result of the reaction in any way, but a course of tuberculin treatment leads to an increase in the complement-fixing bodies of the serum in some cases.

The object of this paper is to draw attention to the need of a further supply of sound dairy stock. Three main arguments in favour of this proposal have occupied our minds: (1) that the loss to the dairy industry through tuberculosis in cattle amounts to a considerable sum each year, (2) that there is serious loss in human lives due to bovine tuberculosis, (3) that, owing to their dearth in the country, there should be sufficient demand for sound dairy stock to place a farm devoted to the rearing of such cattle on a sound financial basis. The last part of this paper deals with a proposal to carry out this scheme.

The present notes have been written in connection with official correspondence regarding the prophylactic inoculation against plague and the study of this and other health problems in India.

1. One hundred lepers were examined by Browning, Cruickshank and McKenzie's modification of the Wassermann reaction with positive results in 22 cases. The amount of complement deviated was in some cases exceptionally large.

2. In a control group of 110 non-leprous persons there were 11 positive reactions.

3. In only one of the lepers was there visible evidence of former venereal disease but 33 of the lepers admitted that they had suffered from syphilis or from chancres, and of these 33, 13 reacted positively, while only nine of the remaining 66 gave positive reactions.

4. In the control group, 21 admitted former syphilitic infection and, of these, eight reacted positively; among the remaining 89, who denied syphilis, there were three positive reactions.

5. There were 12 positive reactions among 44 cases of tubercular leprosy and 10 positive reactions among 56 cases of the anaesthetic type.

6. The average duration of the disease, among the 22 lepers who reacted positively, was four years and eight months, as compared with an average of three years and eight months for the 78 patients who reacted negatively; but among the latter there were many old-standing cases.

7. Seventeen of the 22 positive cases were in an advanced stage of leprosy and in some of them the disease was progressing; but among those lepers who reacted negatively there were also many advanced and progressing cases.

8. Serum from the lesions in 10 of the lepers who reacted positively was examined by dark-ground illumination, but in no case was the Treponema pallidum found.

9. The luetin test was applied to 21 lepers, with negative results in every instance; 13 of these cases gave positive and eight gave negative Wassermann reactions. The test was also applied to a control group of non-leprous persons selected because they were likely to be latent syphilitics. In this group there were 11 positive luetin reactions.

It has been already shown by Darwin and others that reproduction is a function of environment and that unfavourable conditions of life are likely to increase the number of seeds formed or offspring produced; hence so many are reproduced that the chance of the species being perpetuated is maintained, despite the unfavourable conditions for survival. To extend this idea, and say that a dying species tends to reproduce faster than one actively evolving, is a suggestion worthy of enquiry. It has been argued that the varying birth rates in man may to some extent reflect the future biological possibilities of his race. In so far as all environments are really functions of time, or, to put it another way, we measure the nature of an environment by the length of time it takes to produce a certain result, it is quite a natural sequence to consider the effect of time, that is, age on fertility. Dr Matthews Duncan and others have dealt with the immediate effect of time, that is personal age, and the question of the transmitted effect, if any, remains to be considered. If the idea that a species which is dying out tends to reproduce more rapidly, holds good for man, then our previous finding, that the later born do not on the average live so long as the earlier born, would suggest that they might possess as compensation an enhanced fertility. To solve this problem we must correlate the number of offspring produced by each unit with the age of the parents when he or she was born, the reproductive period being made constant.

A vaccine may, in general, be denned as a standardised suspension of killed bacteria. It is true that in a few instances living organisms are employed as vaccines as in the case of the Haffkine prophylactic for Cholera and the sensitised vaccines of Besredka. Notwithstanding these few exceptions it is suspensions of killed bacteria which are in most general use therapeutically as vaccines. According to Wright's method the bacteria employed in the preparation of a vaccine are killed by heat, the temperature actually employed ranging from 53° C. to 65° C. for one half to two hours. This method of sterilising vaccines has been largely employed, but has recently been subjected to much criticism. It has been stated that employment of heat in the sterilisation of vaccines has impaired the value of the vaccine, the heat coagulating albumin, increasing the toxicity and diminishing the immunising properties of the vaccine.