In 1918, Schultz and Charlton1 first reported that the intracutaneous injection of from 0.5 to 1 cc. of normal or scarlet fever convalescent serum would blanch the rash of scarlet fever at the site of injection. They also showed that the blanching substance was present in serum taken after the fourteenth day of scarlet fever, but that serum taken earlier in the disease did not have blanching power. Plain horse serum or diphtheria antitoxin failed to blanch the rash. Schultz and Charlton also made injections of a dilute solution of epinephrine hydrochloride intracutaneously, and found that the rash blanched within a few minutes. This blanching lasted five or six hours. In contrast, the reaction produced by scarlet fever convalescent serum appeared only after five or six hours and lasted several days. Schultz and Charlton expressed the belief that human serum contained some vasoconstricting factor which counteracted the vasodilating effect