Since the demonstration1 (Dicks) in filtrates of scarlatinal streptococci of a toxin which causes a skin reaction in certain persons apparently susceptible to scarlet fever and none in others apparently immune, there has been a tendency to draw a close analogy between the interpretation of Dick tests in relation to scarlet fever and that of the Schick test in connection with diphtheria. It has been assumed that a negative Dick test shows a true antitoxic immunity to scarlet fever; this has been supported by the presence of an antitoxin in serums from patients convalescing from scarlatina and from others in whom the Dick tests were negative which, when added to toxin, neutralizes its toxic action in the skin of a susceptible person. The nature of the skin reaction, its relation to immunity, antitoxin and streptoccocic infection, and the identity of their apparent analogies to the known pathologic processes in