In a Memorandum circulated through the Colonial Office, the Cancer Committee of the Ministry of Health expressed a desire for any available information as to the incidence of cancer upon persons of different races living under similar conditions. While there are a good many parts of the world in which considerable numbers of people of different races live side by side, in few of such places are records available for the purpose of a statistical enquiry.

It is the thesis of this paper that Mendel's principle of varitaion, formed from the study of the genetics of higher plants and animals, can be applied also to bacteria, and that acquired virulence in bacteria is the result of Mendelian variation.

The life tables that have been constructed from the recorded mortality in England and Wales as a whole at more or less regular intervals since registration of death was introduced in 1837, and those that have been prepared for special districts and cities at various times since that date, afford accurate information regarding the average length of life at different periods during the greater part of last century. There is still comparatively little known, however, about the mean duration of life, and the conditions of health on which it so largely depends, amongst those who lived in the British Isles in pre-registration times and the present paper contains the results of and attempt to supplement existing knowledge on this subject. The data on which the paper is based have been derived from two sources, namely, the Index and Epitome of the Dictionary of National Biography and Burke' Peerage and Baronetage. In the first of these are records of the dates of birth and death with brief summaries of the life histories of persons who were selected as being wminent in various spheres of life in the British Isles and the Colonies from the earliest historical period; in the second are given the genealogical histories of members of the different titled families.

Pasteurisation at 62.8° C. (145° F.) for 30 minutes leads to a marked reduction in the total bacterial content of milk, varying for different specimens from 94 to 99·8 per cent., when the process is carried out under the most exact conditions. At lower temperatures, e.g. 60° C., the percentage reduction may vary widely—from 51·6 to 97·4 per cent. The percentage reduction has been found to be slightly less when the same specimens of milk are pasteurised in a large scale apparatus than when treated in small quantities under laboratory conditions, the average reduction being 91·2 per cent, in the former case and 98·4 per cent, in the latter. The reasons for this are discussed.

An effectively pasteurised milk should not contain lactose-fermenting bacilli in 1 c.c, and the B. coli content is a valuable index of the efficiency of a pasteurising process.

Milk containing B. tuberculosis, when pasteurised at 62·8° C. for 30 minutes (1) in tubes in a water bath in the laboratory, and (2) on a large scale by a commercial plant, is rendered non-infective to guinea-pigs. By laboratory pasteurisation, even at 60° C. for 30 minutes, milk containing tubercle bacilli is rendered non-infective.

The “Radiation Integrator in Vacuo” is an instrument designed by a biologist, to assist in the study of solar radiation, as received on the surface of the earth. The principle of the instrument is that a black bulb in vacuo is exposed to the sun's rays; the bulb, which contains alcohol, is connected to a graduated stem maintained at shade temperature; radiant heat from the sun causes alcohol to distil over the bulb into the stem where its volume is measured. In Samoa the shade temperature is practically constant throughout the year, but one believes on theoretical grounds that more radiation is received from the sun between September and March than at the other season, and that the radiation has two maxima, in October and February. This instrument, which has been observed for 12 months, confirms the expectation. The daily mean distillate, the distillate per hour of sunshine (Campbell Stokes) and the mean distillate for the three hours before noon, all show the same seasonal changes.

The instrument has been standardized against Gorczynski's pyrheliometer, so that the readings in c.c. of alcohol can be converted into calories. The instrument is not difficult to make or read, and it can be left in the open in all weathers. It integrates its results and requires to be read once a day in Samoa.

Comparatively few speciallised investigations of the physical development of school children seem to have been made in this country. The most comprehensive British investigation is that made by Arthur Greenwood. This enquiry, based on the published annual reports of the various Educational Authorities, as well as those that preceded it, did not touch the main problem of the present study; viz. the relation between physique and mentality. Miss E. M. Elderton, a year later, made a careful biometric study of the school populatin of Glasgow.

(1) Mice can be readily infected with many strains of B. tuberculosis, both of human and bovine type, by intraperitoneal inoculation with a dose of 0·75 milligramme of moist culture. But, with a fairly virulent culture of bovine type, doses of 0·005 milligramme produced infections of almost the same duration as the larger doses.

(2) The investigation of seven cultures of human and six of bovine type showed that in general the animals infected with the bovine strains survived. for a shorter time than those infected with the human strains. Also, several human cultures failed to produce infection, whereas no failure occurred with the bovine cultures. But no constant difference was found between the duration of infections with the two types of bacilli. Thus rapidly fatal infections were produced by certain cultures of both types.

(3) The period of survival of infected animals depends partly on the particular culture used for inoculation, and partly on the individual resistance of the animal and, in the case of nearly full-grown mice, is independent of their weight at the time of inoculation.

(4) The effect of repeated passage of tuberculous material from mouse to mouse without interposing cultivation of the bacilli on artificial media was investigated with eight strains, the series of passages numbering from three to eight. Increase of virulence was repeatedly observed, but such increase was never maintained in subsequent passages. The evidence indicates that the individual host plays an important part in modifying the virulence of the organisms for other members of the same species.

(5) As regards maintenance of virulence, comparatively constant results were obtained with different subcultures of the same strain. But repeated tests over a period exceeding five years have given indications that the virulence of a strain may become altered spontaneously from time to time.

In a previous paper (Stewart, 1926), we have seen that the mutabile form of B. neapolitanus Emmerich is a heterozygote with a Mendelian formula IiFF, in. which F represents a unit character for the fermentation of a particular sugar, e.g. lactose, I represents a factor for the inhibition of F, and i represents the absence of I in a pair of allelomorphs. Similarly paracolon has a formula IIFF.

The problem which we shall discuss in this communication is of great importance, is perhaps the most important of all epidemiological problems, and we are far indeed from supposing that we have solved it. We think, however, that the work we have done is certainly useful in enabling us, and others, to state the problem correctly, and possibly useful in suggesting a first approximation to its solution.