_Prophylaxis by Immunization._—The best-known bacterial prophylactic is that of Haffkine. Stalactite bouillon cultures are grown in flasks for five to six weeks. The organisms are then killed by heat at 65°C. for one hour. Phenol (½%) is then added and from 0.5 to 4 cc. injected according to the age and size of the individual. Ten days later a still larger amount is injected. The reaction following these injections is apt to be quite severe. Recent reports show that of 118,148 inoculated persons the plague incidence was approximately 8 per 1000 while among 321,621 noninoculated the incidence was 34 per 1000. Statistics from Sagaing show 19 cases with 7 deaths among 4284 inoculated persons while there were 134 cases and 128 deaths among 4467 not inoculated. The plague mortality in cases which had previously been inoculated was 40% while that among the noninoculated was 78%. From the above it will be seen that incidence is reduced to about one-fourth and mortality about one-half as the result of the use of Haffkine’s prophylactic. Besides this killed culture other material has been used. Lustig and Galleotti used the nucleo-proteid from plague bacilli for subcutaneous injection. Kolle and Strong have recommended a vaccine of living but nonvirulent plague bacilli. A higher degree of immunity seems to be conferred by this living vaccine but there are certain dangers in the use of living organisms which outweigh the advantage noted above. Yersin’s antiplague serum, which is prepared by injecting horses at first with killed cultures and later with living plague bacilli, may be used as a prophylactic as well as in treatment. One point to consider is that such serum, if used immediately after taking from the horse, might contain living plague bacilli. The phenol preservative prevents this. It must be remembered that this is a passive immunization as against the active one with Haffkine’s prophylactic, hence the protection is very short, only ten days or two weeks as against the more enduring immunity of a year or so following Haffkine’s prophylactic. It must be remembered that anaphylactic manifestations may follow the repeating of the dose of Yersin’s serum. It is probably advisable for one who is to be exposed to plague for a short time only to receive an injection of the serum. As regards pneumonic plague there seemed to be little protection attaching to either active or passive immunization.