Scarlet Fever Toxin in Preventive Immunization

After the production of experimental scarlet fever, 1 it was demonstrated that Berkefeld W filtrates of the hemolytic streptococcus, used in the successful inoculations, contain a toxic substance. When injected intracutaneously, in the proper dilution, this substance gives skin reactions that can be used to determine susceptibility to scarlet fever. 2 It was also shown that the toxicity of the filtrate is neutralized by addition of convalescent scarlet fever serum; and that persons who show positive skin tests before passive immunization with convalescent serum give negative tests afterward. These results suggest that we are dealing with a toxic substance specific for scarlet fever, and that it might be used in the production of active immunity. After a number of preliminary tests to determine what amounts of the filtrate, injected intramuscularly, might be expected to give a reaction, the following attempts at immunization were made: Experiment 1. —A healthy girl, aged