1. B. bifidus communis, first isolated and described by Tissier, is the predominant organism in the intestinal flora of healthy breast-fed infants in the early weeks of life. In films of the faeces at this period Gram-positive bacilli may constitute almost 99 per cent. of the organisms present.

2. B. bifidus requires fairly strict anaerobic conditions for its isolation in primary culture; but thereafter it grows readily in sub-cultures in the presence of oxygen.

3. B. bifidus is a member of the acid-tolerant group of Gram-positive, faecal organisms. Although closely resembling B. acidophilus, it is distinct from the latter morphologically and also in certain of its cultural characters. The results of agglutination reactions indicate that different strains of B. bifidus are not serologically uniform.

4. Although B. bifidus is a very pleomorphic organism, no evidence was obtained in the present work that it could be changed into an aerobic, spore-bearing bacillus.

5. The predominance of B. bifidus in the intestinal flora of breast-fed infants appears to be closely related to the high degree of acidity of the faeces of these infants. It is probable that the predominance of B. bifidus over other organisms is an important factor in preserving a healthy condition of the intestinal tract in the breast-fed infant.

The “chronic irritation” theory still retains its interest, though it has not yet provided a thoroughly satisfactory explanation of the origin of that stimulus to growth which causes normal tissue to become malignant. If employed with caution, ideas borrowed from bacteriological work on “transmissible autolysis” may be contributory in the search for the explanation which is desired.

It is important to maintain a careful distinction between the initiation and the continued propagation of the malignant variant.

It seems hazardous to assume that one can apply as immediately valid for cancer those ideas about the natural and acquired resistance of the host which are current in bacteriological literature. On the other hand, it is not suggested that such ideas should be discarded but rather that they should be regarded as suggesting alternative possibilities, none of which can be definitely excluded.

Analogies with immunological reactions to foreign protein (bacterial or animal) certainly suggest the possibility that the cure of cancer may be found in discovery of “the right antibody for the right antigen”; but it is not clear how far such analogies can be accepted as being entirely appropriate; still, owing to the likelihood that new kinds of antigens and antibodies will be discovered, continued search for these factors in cancer is of high importance.

In the present article, which is a sequel to a former discussion on stimulants to bacterial variation, I have considered whether the idea of a stimulus to the production of non-viable variants may be regarded as of immunological interest in relation to the therapeutic problem of cancer.

I have endeavoured to show that this idea is worth consideration, provided that its importance is not exaggerated and that it is correlated with better established data about the principles of immunity.

Since the birth-rate is persistently diminishing, interest in the laws by which nativity is governed is steadily increasing. This interest became still more intense when, on account of the war, a large number of human lives were destroyed, causing a decrease of population in many countries. Those who fell in this war happened to be men in the prime of life, a fact which manifested itself after the war in a decreased number of births, apart from the temporary increase of births in consequence of the return of the mobilised men to their native towns.

The German social statistician Sombart rightly asserts that in many cases we obtain a sharper and better impression by limiting our investigations to the conditions prevailing in a single year-class than by taking several ageclasses together, which are always in some respects heterogeneous.

In a recent report (Topley, Wilson and Lewis, 1925) we described some observations on the rôle of the Twort-d'Herelle phenomenon in the epidemic spread of mouse-typhoid. In the experiments there recorded the lytic filtrate was administered by the mouth. The results obtained did not suggest that such administration exerted any appreciable influence on the spread of disease. It was shown, in a separate series of experiments, that intraperitoneal inoculation of such a filtrate afforded a marked degree of protection against subsequent inoculation of living cultures of B. aertrycke, provided that sufficient time had elapsed to allow of an immunising response, that no immediate protection was afforded by the inoculation of the lytic filtrate, and that neither immediate protection, nor subsequent immunisation, was afforded by the administration of the lytic filtrate by the mouth.

When diphtheria toxin is injected in a suitable form and in sufficient quantity into an animal, antitoxin will presently appear in the blood. If the injection be made into an animal that has not previously received a stimulus there is a latent period of about three weeks before any antitoxin can be detected. The amount present in the blood gradually increases, reaching a maximum about eight weeks after the injection, and then a gradual fall in level of antitoxic content is seen. If, however, the same amount of the same antigen be injected into a previously treated animal, antitoxin appears in the circulation at a far greater rate. The latent period is only three days, and the maximum antitoxin level is reached in about eight days. The maximum level reached is from 10 to 100 times that reached after an injection into a normal animal. The two types of response are illustrated in Charts 1 and 2 and also in Chart 3, which shows the antitoxic content of a horse after two separate injections of a toxin antitoxin mixture. There is a great contrast between the extent and rapidity of the antitoxic response on the two occasions.

The incidence of goitre among school-children in New Zealand has been determined by the examinations made by one of us (Hercus) and by the officers of the School Medical Service, of over 80,000 children. The proportion of men of military age who were unfitted for active service on account of goitre was ascertained during the examination of over 135,000 recruits by the Military Medical Boards in the years 1916–1918. Additional information has also been derived from hospital records, by the number of operations for goitre.

The amount of iodine has been determined in nearly five hundred samples of soil, obtained from all parts of New Zealand, together with samples of a number of waters from mineral springs and town supplies.

In order to ascertain whether any relation exists between the amount of iodine in the soil of any district (considered as a soil of plant food, and therefore indirectly of human food), we have divided the Dominion into thirty-three districts, each homogeneous as far as possible in its geological and geographical circumstances, and have ascertained the average amount of iodine in soil and average incidence of goitre among school-children within each district, utilising certain defined methods of soil-analysis and diagnosis of goitre. It is proved that the following relation is approximately true throughout: viz, percentage incidence of goitre among school-children is equal to 6 plus the quotient of 360 divided by the amount of iodine in ten million parts of soil, so long as this does not exceed 50, assuming defined methods of medical examination and chemical analysis. When the soil is abnormally rich in iodine the constant 6 must be diminished. Further (though the records are here less complete), the relation between the average amount of iodine in the soil and the percentage of military recruits medically rejected on account of goitre is of the same general nature, the latter figure being about one-twentieth of the incidence among school-children, though this proportion must also be diminished in regions in which iodine is particularly abundant.

Approximately, therefore, the incidence of the disease is inversely proportional to the amount of iodine in the soil. Further, where, though the incidence of goitre is low, the amount of iodine in the soil is abnormally low, we have proved that it is present in the water supply in greater amounts than usual, and the daily intake of iodine among the inhabitants of such a district is thereby maintained. Further, regions in which the average amount of soiliodine is low are also those in which goitre is most frequently seen amongst the domestic animals.

Though there are certain points as yet unexplained, the whole body of facts is too large, and the relationship too consistent, to be fortuitous. We believe, therefore, that the hypothesis that goitre is caused by a deficiency of iodine in the diet has been fully sustained by the present investigation. Reasons have been deduced also for believing that a relation holds between the incidence of goitre and the distribution of geological formations (as determining the nature of the soil) in New Zealand, Switzerland, and perhaps in other countries.

Further, a study has been made of the prophylactic treatment of schoolchildren in New Zealand, by administering small amounts of iodine weekly. This has hitherto had fairly good results. We believe that the best method of prophylaxis, considered on physiological grounds, as well as those of efficiency and economy, would be daily ingestion of minute amounts of iodine, obtained by the utilisation for all culinary and table purposes of an iodised salt, in which 1 part of potassium iodide had been added to 200,000 of sodium chloride—the method which has been attended by such satisfactory results in Switzerland. This would afford the minimum amount of 0·005 mg. per day, which seems necessary for the functional requirements of the thyroid gland, while it would be far too small to have any ill-effects in the production of hyperthyroidism.

A consideration also has been given to the source of the iodine in soils and natural waters in the light of our own analyses and those of previous investigators, especially Dr Th. v. Fellenberg, whose work has been of the greatest assistance to us.

That the mortality from cancer shows definite variations in different parts of England is now generally believed. Various attempts have been made to ascertain whether any association exists between this variation in mortality and variations in certain features such as elevation and levelness of site, nature of soil and underlying geological formation, proximity to rivers liable to floods, etc., that characterise the several districts comprising different regions, and evidence both for and against the influence of one or other of these factors in predisposing to cancer has been brought forward at different times. An inquiry (1922) into the incidence of cancer in the registration districts in the Severn Valley for the decade 1901–10 seemed to indicate that no definite connexion existed between an excessive mortality rate from cancer and the foregoing factors. It was considered advisable, however, to continue the investigation in another part of the country to determine if the inferences drawn from the analysis of the Severn Valley data were confirmed or if any new features were brought to light. The region chosen included the districts drained by the Yorkshire Ouse, the Trent, the Cambridgeshire Ouse, and those that intervene.

In the handling of milk no single factor is of more importance than the cleanliness of the vessels used, and steam sterilisation is an essential part of correct cleansing technique of dairy utensils. Although several hundred dairy farmers have installed apparatus for steam sterilisation, the majority are still content with less efficient methods and rely upon “scalding” as the final operation in washing a utensil, although the water used for scalding is seldom at a sufficiently high temperature to kill many bacteria, and it is usually poured from one vessel to another in the hopes of efficiently finishing the cleansing processes although it is only comfortably warm to the fingers.

That the human race is extremely susceptible to the ravages of measles is well known, Brownlee not being guilty of much exaggeration when he states that, in the presence of infection, the only way to avoid this disease is to have had it. MacNalty (1918) states in his report on the subject to the Local Government Board that “the disease is so universal in this country that few children escape it,” this being particularly true in reference to the poorer urban classes. Butler (1913) found as a result of the study of the statistics for the public elementary schools of Willesden that among persons who had attained the age of 15 and upwards, only 2·7 per cent. had escaped measles. Zingher states that amongst children who have not previously suffered from the disease, and who are exposed to it, between 96 and 98 per cent. will develop it.