Views as to the possibility of inducing immunity with inactive virus are still divergent. In experiments carried out by one of us (Kligler, 1932) with fowl-pox virus, the results were entirely negative. The prevailing conception based on repeated negative results is that at best only a slight or transient immunity can be induced with inactive virus. A comprehensive critical review of the literature dealing with this aspect of the problem is given by Parker and Rivers (1936). The restudy of this problem was undertaken as a result of our findings with Rickettsiae (Kligler and Aschner, 1934). In a series of experiments in which relatively large amounts of infected brain emulsions inactivated in various ways were injected into guinea pigs, the results were consistently negative; as much as 3 grams of brain tissue failed to produce more than a slight and irregular increase in the resistance of the treated guinea pigs to an infection with active virus.