1. Intraperitoneal injections of killed and living broth cultures of a virulent pneumococcus produce in guinea pigs a high degree of active immunity and a serum with strong protective power.
2. Despite the protective power of such serum no agglutinins for the homologous organism and no precipitins for soluble derivatives were demonstrable.
3. Guinea pig immunity to pneumococcus infection produced by the method described is not attended by cutaneous allergy to derivatives of the pneumococcus used for immunization.
4. During the course of an artificially produced active immunity, anaphylaxis may at times be present and at times absent without any measurable effect upon the resistance of the animal to infection by intraperitoneal injection.
5. In the particular instance studied, the experiments indicate that anaphylaxis to pneumococcus protein has no important effect upon the resistance of the animal to infection. It appears to be a concomitant without any significant rôle in the immunity mechanism.