In 1923, we succeeded in producing experimental scarlet fever with an apparently pure culture of a hemolytic streptococcus isolated from a case of scarlet fever.1 The Berkefeld V filtrate of this culture did not produce scarlet fever in a person who later developed the disease on inoculation with the unfiltered culture.
In the series of inoculation experiments in which scarlet fever was produced, only two of the ten volunteers acquired the disease. These ten volunteers were young adults who said that they had not had scarlet fever. They were all inoculated with the same culture. The failure of some to acquire scarlet fever, while others developed it in a typical form, was probably due to a difference in susceptibility.
Attempts to demonstrate immunity to scarlet fever by means of skin tests had previously been made. In 1916, we2 described the reaction occurring in convalescent scarlet fever patients on