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470 or intramuscular injection. I believe to be of great value the method worked out by Pfeiffer for comparing all such varieties with one selected as typical, which he employed for the preparation of an antitoxic serum. This method will be found of efficient help in distinguishing specimens of the greatest affinity with the average cholera comma. But once such specimens are selected and their particular properties studied, they begin to change from the first day they are introduced into the laboratory, and no calculation based on these studies is possible. In a case quoted by Metchnikoff, the proportion of the initial power of the microbe, and the strength it showed at a later trial, was as 75 to 1, the microbe having gradually sunk to 1/75 of its initial virulence." These remarks, by so great a master of the subject, whilst they indicate a way of reconciling many apparent discrepancies in matters of fact and differences in the conclusions arrived at by different bacteriologists, and whilst they indicate a key to many of the clinical features of cholera, teach us caution in accepting as proved the causal relationship of the cholera vibrio to the disease with which it is so invariably associated.

Symptoms.— An attack of cholera commences in one of two ways: either it may supervene in the course of what appears to be an ordinary case of diarrhœa, or it may come on suddenly and without any well-marked prodromal stage. During cholera epidemics diarrhœa is unusually prevalent. It is a common observation that at such times an attack of this latter nature, after a day or two, may assume the characters of true cholera. The preliminary looseness in such cases is called the "premonitory diarrhœa." Whether this looseness is specifically related to the subsequent attack, or is of an ordinary catarrhal or bilious type and acts simply by predisposing to the specific disease, has not been determined. Possibly, owing to a catarrhal condition— in itself non-specific —the resisting power of the mucous membrane is impaired; possibly, in diarrhœa, the large amount of fluid in the gut affords a favourable medium