During the last two years we have encountered from time to time in the course of our work of immunization against scarlet fever, both by the hypodermic and by the intranasal method, reactions that appeared inconsistent and strikingly at variance with what had been anticipated. In our1 publication on the subject we endeavored to account for such unexpected results by advancing the hypothesis that in some individuals the level of immunity to scarlet fever may vary from time to time, under the influence of factors beyond our knowledge. In the last six months the conviction has been forced on us that other factors play a part in the causation of these unexpected reactions. The experiences that led to this conclusion deserve, we believe, to be set forth in detail.
During November and December of 1934 we obtained from the use of one particular batch of Squibb's Dick Toxin uniformly