Cultures of a hemolytic streptococcus isolated from a human case of erysipelas were tested for ability to produce lesions by injecting various amounts intradermally in shaved rabbits. Severe lesions could be developed at will in this way despite the fact that intravenous or intraperitoneal inoculations of large doses of the cultures failed to kill. The lesions were of two sorts, phlegmonous and erysipelas-like.
A serum capable of warding off the injurious action of the streptococcus on the skin was procured from animals receiving repeated intracutaneous inoculations of the organism. Normal serum by contrast had no protective effect.
By intradermal injections at several points in the same normal rabbit of small quantities of mixtures of equal parts of serum and various dilutions of a suspension of streptococci it proved possible to test sera for the presence of substances protective against the streptococcus.