the plague prophylactic the activity of the microbes is arrested before it is inoculated, and the effect can be regulated, as mentioned above, by simply measuring up the doses in the same way as is done with any chemical drug. The expectation formed when devising the plan for the plague prophylactic has been very fortunately justified, and an advance on the results from the cholera vaccines was obtained; but I can not yet say certainly whether this favorable result is indeed due to the particular provisions which I had made for obtaining it. The effect of the plague prophylactic was first tested at the Byculla Jail, in Bombay, when the epidemic reached that establishment. From the first day after the inoculation till the end of the outbreak there were in the jail twelve cases and six deaths among one hundred and seventy-two uninoculated inmates, and two cases, with no deaths, among one hundred and forty-seven inoculated. A year later, almost exactly a similar result was observed when the plague attacked the so-called Umarkhadi Common Jail, in Bombay. In this case after the inoculation there were ten cases and six deaths among one hundred and twenty-seven uninoculated inmates, and three cases, with no deaths, among one hundred and forty-seven inoculated. These and other observations show that the vaccine for the plague begins to exercise its effect within some twenty-four hours after inoculation; that it is useful even in the case of persons already infected; that it is therefore applicable at any stage of an epidemic. Numerous further observations were soon collected on the working of the system.