268 STUDIES IN IMMUNITY. 



fully with experiment. The explanation is unquestionably ingen- 

 ious but the existence of certain of the substances, particularly 

 of toxons, is purely hypothetical. The question, then, is still an 

 open one. 



MODE OF ACTION OF ANTI-ALEXIN ON ALEXIN. 



We might have expressed the preceding elementary ideas some 

 time ago. In fact, they were suggested to us by some experiments 

 we did on the neutralization of alexin by anti-alexin in 1900 at the 

 Pasteur Institute (Professor MetchnikofFs service). But it seemed 

 well to render the study more complete by considering the effect 

 of certain other toxins on their antitoxins. We have not as yet 

 been able to carry out this work. We shall therefore limit our- 

 selves here to a consideration of the facts we obtained some time 

 ago so as to obviate their future consideration. 



We may consider, then, the effect of a suitable anti-alexin; that is 

 to say, the serum (heated to 55 to 56 degrees) of an animal of species 

 B that has received two or three injections of fresh serum from 

 species A, on the alexin in the fresh serum of A.* 



Having mixed these two antagonistic sera we need a reagent 

 capable of detecting whether or not free alexin is present. For this 

 purpose we use red blood bells well sensitized by a specific hemolytic 

 serum (55 degrees). We know that alexin is absent when these 

 cells remain intact. 



Such an experiment naturally comprises a control mixture con- 

 taining the same factors as the preceding mixture, but with heated 

 serum from a normal animal of the same species as the one that 

 furnished the anti-alexic serum. 



As may be imagined, our first experiments are to determine 

 whether the reactions of our antagonistic sera will give the "Ehrlich 

 phenomenon," which is so difficult to reconcile with the hypothesis 

 of neutralization according to fixed proportions. In the following 

 experiments certain precautions must be taken to avoid experi- 

 mental error. In the first place only a single antitoxic effect, namely, 

 the one against the alexin under consideration, must be allowed to 



* An anti-alexic serum must be heated to 55 degrees to destroy its proper alexin, 

 in a study of this sort. The only alexin in the experiment should be in the form 

 of the fresh serum of the animal against which the antiserum is active. (See 

 " Homolytic sera, their antitoxins, etc," p. 186.) 



