That many epidemics of enteric fever have been caused by contamination of central water-supplies is beyond dispute, but evidence is accumulating that makes it difficult to attribute its widespread prevalence in endemic form in India and elsewhere to this cause. It is necessary, however, to guard against assuming that therefore the disease is not water-borne. There are in India innumerable chances of water, when stored for domestic use, being contaminated, besides the same possibility in the case of food, feeding utensils, and cloths used for cleaning them. And when it is claimed that dust or flies play an important rôle in its dissemination, it is not necessary to assume that the bacillus is taken into the mouth or respiratory passages directly, but rather that it is conveyed to water, &c., by means of dust or flies.

Finally I wish to draw particular attention to the following facts:—

1. The striking diminution in the case-mortality at the Mile End Hospital which followed the systematic use of antitoxin.

2. The subsidence of the epidemic during the season when diphtheria is commonly most prevalent.

3. The opening of the schools in September without any increase in the prevalence of the disease.

4. The persistence of diphtheria bacilli for long periods in certain of the convalescents and contacts.

5. The success of preventive measures based upon the belief that diphtheria is spread mainly by personal contact, and through the inter-mediation of healthy persons and other who by the means usually employed are not recognised to be suffering from the disease.

In this outbreak of diphtheria certain individuals suffered from diphtheria, and others from sore throat probably diphtheritic. These individuals obtained their milk supply from two cows. Members of one household who did not drink milk, or who used it only after sterilisation, escaped infection. The cows yielding the milk were found to be suffering from an eruptive disease of the udder, and both from the lesions and from the milk cultures of virulent diphtheria bacilli were isolated. The pathological condition in the cows preceded, by a short interval, the onset of the disease in the patients. Having regard to Power's epidemiological investigations, and to Klein's experimental work, this observation was of the greatest interest and naturally suggested the hypothesis that the lesions were due, primarily, to a specific diphtheritic infection of the cow. Further investigations weakened this view, for it must be noted:—

(1) That in a cow intentionally submitted to infection from the diseased cows and in which there occurred the eruptive condition of the udder, neither in the vesicular nor in the ulcerative stage of the disease could diphtheria bacilli be demonstrated.

(2) That in calves infected with the eruptive disease no diphtheria bacilli could be demonstrated.

(3) That in a calf, in spite of the fact that it had received 10, 000 units of diphtheria antitoxin, the vesicular eruption was experimentally produced. The last is probably the strongest point in support of the dual nature of the condition in the cows.

It is conceivable that pathological lesions in the cow such as those described, if infected with the diphtheria bacillus, might form a suitable nidus for its growth and permit of the infection of large quantities of milk over a considerable period. Though we have as yet no evidence on the subject it is possible that a profound change in the virulence of the diphtheria bacillus for the human subject might be effected by such passage through the cow1.

The disgusting habit the milkers in this part of England have, of spitting on their hands before milking, would easily account for the infection of the lesions, even in the absence of obvious diphtheria in the cowman; knowing, as we now do, that apparently healthy individuals are not uncommonly the hosts of the diphtheria bacillus.

The experiments made with the view of ascertaining whether the eruptive condition was genuine cowpox, are opposed to that view; for two calves, and one cow successfully infected with the eruptive condition and subsequently vaccinated with vaccine lymph, developed a typical vaccinia.

The somewhat limited time and material available have prevented us from investigating the matter so fully as we should have wished, or on a scale proportionate to its interest and practical importance. We hope at some future time to go further into the matter.

Our best thanks are due to Mr Sidney Villar, F.R.C.V.S., for bringing the outbreak to our notice, and for his help in the veterinary side of the question; and to Dr Carson Smyth for his kindness in allowing us facilities for taking cultures from the throats of his patients.

Shanghai is situate in the sub-tropical zone and has a climate of wide variation of temperature, but is broadly tropical during the summer quarter and temperate for the rest of the year. Lying on the alluvial flat of the Yangke delta the conditions of soil and sub-soil are uniform in all parts of the Settlement. The ground water-level is about five feet below the surface.

The following notes are to serve as a postscript to the paper which appeared under the above title in the preceding number of the Journal of Hygiene (pages 1—42).

The primary object of these papers is to attempt to give a brief review of the present state of opinion regarding the many questions involved in the subject of immunity,—a review intended chiefly for those whose work is concerned with other fields of hygienic research. The carrying out of this aim has necessitated the re-statement of many facts familiar to bacteriologists, in order that the continuity of the discussion might be maintained. Wherever it has been considered advisable the details of the data which have formed the basis of theory have been given, but as a rule the leading results have been alone dealt with, partly because details might obscure the general principles it was intended to emphasise, partly because considerations of space have made an exhaustive treatment of the subject impossible.