Owing to the consumption of water from the ponds or tanks belonging to these villages, the inhabitants of the bustees are subject to periodic visitations of cholera. It was in one of these bustees that the first observation was made as to the effect of the cholera vaccines.
The spring is essentially the cholera season in Calcutta. About the end of March two fatal cases of cholera and two cases of choleraic diarrhoea occurred in Katal Bagan Bustee, in a population grouped around two tanks. This outbreak led to the inoculation of one hundred and sixteen persons in the bustee out of about two hundred. After the inoculation there occurred nine more cases of cholera, seven of which proved fatal, and one case of choleraic diarrhoea. All the ten cases occurred among the uninoculated portion of the inhabitants, which formed the minority, none of the inoculated suffering. The results were more interesting when analyzed in detail. Some of the cases had occurred in families in which some of the members had been inoculated and others not, and the disease selected the non-inoculated members, sparing the inoculated. Thus, in one house six members out of eight had been inoculated. The attack, a fatal one, occurred in one of the remaining two. In another house eleven members out of eighteen were inoculated. The eleven members remained free while four out of seven not inoculated were attacked.
Upon these observations the Calcutta municipality felt encouraged to vote funds for the continuance of the inoculations in an experimental farm, and appointed for that purpose a special staff. In 1896 the result of two years' observations were embodied by the health officer in a report to the Calcutta Municipal Corporation. It recorded a most satisfactory state of affairs. During the time under observation some eight thousand persons were inoculated. Cases of cholera occurred in seventy-seven huts in which some members of the family had been previously inoculated and others not. Comparing the incidence of the disease in the two groups, a striking advantage was found to be with the inoculated. I made an analysis of the cases according to the time which had elapsed between inoculation in each of these huts and the occurrence of cholera in them, and the following results were found. During the first four days after inoculation, apparently before the vaccine had time to produce its full protective effect, there were proportionately 1.86 times fewer deaths among the inoculated than among the non-inoculated members of the families. In a second period, extending from the fifth to the four hundred and twenty-ninth day—i. e., for fourteen months—there were 22.62 times fewer deaths among the inoculated; while in the last period—that is, between the four hundred and thirtieth and seven hundred and twenty-eighth day after the inoculation—there were only 1.54 fewer deaths among the inoculated, the immunity having evidently gradually disappeared. The net