With the increasing interest in prophylactic typhoid vaccine inoculations, the question frequently arises as to what is the best method of judging the protective power created in the serum of the vaccinated individual. It has been claimed by Leishman1 that there is a certain relation between the appearance of the agglutinating and the bactericidal power in the serum of vaccinated individuals. Therefore, the agglutinating power of a serum is probably some indication of its protective power. The work on which this paper is based has consisted of the study of the agglutinating power in the serum of typhoid fever patients, the development of typhoid agglutinins in rabbits' serums, and the effect of their serums on that of other rabbits.
In Osler's "Modern Medicine," it is stated that almost all cases of typhoid fever sooner or later develop in their serum the power to agglutinate the Bacillus