1. Attempts to produce anaphylactic shock in white rats by second intravenous or subdural injections of horse serum have failed.
2. It was impossible to demonstrate either by skin reactions or by the uterine reaction that white rats can be sensitized to horse serum.
3. It was not possible to sensitize guinea pigs passively with the serum of white rats presumably immunized to horse serum.
4. In spite of the fact that the white rat could not be made anaphylactic to horse serum, the tissues of the animal reacted with the horse serum to form precipitins in fair concentration and the antigen disappeared from the circulation soon after the precipitins reached their greatest concentration in the blood.
5. These experiments would indicate that in the white rat anaphylaxis and precipitin formation are independent and represent different types of immunological processes.