The Precipitin Reaction

Important as previous studies on hemolytic streptococci as a cause of scarlet fever may be, especially immunologic studies, convincing proof of etiologic relationship of hemolytic streptococci to scarlet fever was lacking until the Dicks produced the disease in human volunteers with pure cultures of this organism. 1 They have also developed a presumptive susceptibility test by the intracutaneous injection of filtrates of cultures containing the specific toxin, 2 a method of active immunization 3 and of producing an antitoxic serum in the horse, and a procedure for identifying scarlet fever streptococci through the neutralization of toxin in vitro with the serum of convalescents from scarlet fever and experimentally produced antitoxic serum. 4 Indeed, the problem of scarlet fever appears solved, yet the question of relationship of scarlatinal streptococci to other streptococci and the reason for the occurrence of epidemics remains unanswered. In epidemics of scarlet fever, as in other epidemic