Abstract
Introduction In a recent report from this laboratory (1), a method was described which makes possible the study of some aspects of the union between specific antigen and the skin of horse serum-immunized rabbits. The method embraces the interplay between two types of immune reactions: diphtheria toxin with antitoxin and horse serum antigen with the skin of horse serumimmunized rabbits. The method is an indirect one, being based on the observation that horse serum diphtheria antitoxin does not possess the same neutralizing range for diphtheria toxin in normal and in horse serum-immunized rabbits in vivo. If a lethal amount of diphtheria toxin and its neutralizing quantity of antitoxin are injected some distance apart into the skin of both a normal rabbit and a horse serum-immunized rabbit, the former animal will survive and the immunized one will succumb. In the normal rabbit, the toxin and the antitoxin apparently diffuse from the area of injection and neutralization of the toxin takes place in vivo.