IN view of the notable degree of protection against rabies afforded dogs by a single 5 ml. injection of commercial chloroform-treated vaccine containing 33 !3 per cent brain material, as reported in a previous paper,' it was deemed advisable to repeat this experiment. In order to eliminate, as far as possible, variability due to differences in age and batch of vaccines and test virus inoculum, such as occurs when several successive small groups of animals are used for a study of this kind, the experiment herewith reported was undertaken with a single large group of dogs. The question has arisen in regard to the chloroform-treated vaccine as to whether it was the use of this particular chemical inactivating agent or the high brain concentration which was responsible for the considerable degree of protection obtained by us in dogs vaccinated with this preparation.1 In order to answer this question we requested a commercial house to provide us with chloroformand phenoltreated vaccines of identical brain concentration. These were tested in parallel. Rabies vaccines deteriorate rapidly