1. The type-specific carbohydrates (haptens) of Pneumococcus Types I, II and III, when isolated in protein-free form, are devoid of the property of inducing active anaphylactic sensitization in guinea pigs.
2. The bacterial carbohydrates of Pneumococcus, of which the Type II and Type III substances are nitrogen-free, produce rapid and fatal anaphylactic shock in guinea pigs passively sensitized with the precipitating serum of rabbits immunized with pneumococci of the homologous type; the reactions induced are type-specific.
3. In contrast to the positive results with immune rabbit serum, there is a complete absence of anaphylactic response to pneumococcus carbohydrate in guinea pigs passively sensitized with antipneumococcus horse serum.