Knowledge of acquired immunity has been evolved largely as a result of studies on bacterial or virus infections. In attempting to apply this knowledge to syphilis, the investigator is confronted with baffling problems. Bacterial or virus infections are usually followed by complete recovery, which opens the way for the study of acquired immunity. In syphilis, the question of complete cure is not yet fully settled, a fact that renders the problem of immunity correspondingly difficult. Furthermore, the clinical syndrome in bacterial infections is different from that in syphilis with its various stages and late manifestations. It was perhaps to be expected that the immunologic syndrome in the two types of infection would also differ.
As far as man is concerned, natural immunity in syphilis apparently does not exist. While the intensity of the reaction to syphilitic infection might vary in different persons, all appear to be susceptible. Furthermore, only man