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N a previous paper I reviewed briefly the history of preventive inoculation and described the results of my attempts to secure a 'virus fixé' in the case of cholera. It will be remembered that the two vaccines finally obtained protected guinea pigs successfully against all possible forms of cholera infection.

It was now necessary to ascertain whether the same protection could be given to man which was observed in animals. For this purpose it was essential to first of all prove the perfect harmlessness of the operation. This was established by very careful observations of medical men and scientists who were inoculated in Europe soon after the results of the above investigations were published. The inoculation causes a rise of temperature and general discomfort, which lasts one or two days, and some pain at the seat of the injection, which disappears in a few days. The fever and discomfort induced are, on the whole, shorter in duration, though often more intense, than those caused by vaccination against smallpox. The effect disappears within a few days and the individual returns to his usual condition of health.

The next and all-important stage was to devise an experiment or a series of experiments on man so as to test the efficiency of the method against cholera attacks. This part of the investigation could only be done in a cholera-stricken country, where opportunities would arise of comparing the incidence of the disease in inoculated and uninoculated. Such opportunities are limited. Except in certain parts of India and China, cholera appears in localities unexpectedly and does not last long. In the places where the disease is endemic the cases are scattered over large areas. These features rendered the demonstration of the effect of the vaccine a matter of particular difficulty. In 1893 I went to India, and in the course of a year inoculated some twenty-three thousand people in the northern parts of the country; but no cholera appeared in their midst to show whether the vaccine was of value or not. In the spring of 1894 the inoculations were introduced into Bengal, and, with the assistance and co-operation of Prof. W. J. Simpson, of King's College, London, at that time Health Officer of Calcutta, and of his staff, efforts were made to induce the inhabitants of the bustees of Calcutta to get themselves inoculated. These bustees are isolated villages consisting of groups of mud huts inhabited by the poorer class.