HEMOLYTIC SERA AND THEIR ANTITOXINS. 215 



neutralize either of the other mixtures. Let us add, then, to the 

 most strongly hemolytic mixture, namely sensitizer plus guinea-pig 

 alexin, some of our heated antitoxin (0.8 of a cubic centimeter). 

 The mixture becomes harmless for rabbit corpuscles. The addition 

 of the same amount of antitoxin to either of the other mixtures con- 

 taining rabbit or rat alexin does not produce any neutralizing effect. 

 This result, then, is contrary to a logical deduction from Pfeiffer's 

 theory.* On the contrary, the results are quite explicable: the 

 different alexins act directly on the sensitized corpuscles to destroy 

 them. And the antitoxin, being specific for guinea-pig alexin, nat- 

 urally affects the activity of this alexin only. 



With this we conclude our remarks on the theories of the cytolytic 

 sera. To sum up, our theory, offered in 1895, explains all the facts 

 observed and is in disagreement with none of them. From a general 

 standpoint this theory and facts on which it is founded contains 

 three general ideas : 



1. Artificial immunization simply renders the cytolytic mani- 

 festations of normal serum specifically more intense. This con- 

 ception we demonstrated by showing that both normal and immune 

 serum (cholera serum) produce a similar effect on the cholera vibrio, 

 which effect, however, is of unequal intensity in the two instances. 

 This conception has been confirmed by our being able to exalt the 

 hemolytic activity of a given normal animal's serum by vaccinating 

 the animal against red blood cells. 



2. The immunized animal does not have its cytolytic substance 

 increased over normal, but simply produces a large amount of the 

 specific substance which favors the activity of the cytolytic sub- 

 stance, f 



3. A reaction of immunity, consisting in the production of an 

 antibody, noted in an animal injected with harmless cells, such as 

 red blood corpuscles, is identical with the reaction shown by an 

 animal to an infective agent, for purposes of protection. 



* Such an experiment naturally comprises suitable controls containing heated 

 normal rabbit serum instead of the antitoxin. Hemolysis occurs in all the control 

 mixtures and most markedly in the one containing guinea-pig alexin. 



t The mechanism by means of which the sensitizing substance favors activity 

 has recently given rise to interesting studies. Among them may be mentioned, 

 in particular, the researches of Ehrlich and Morgenroth, which have been discussed 

 in the present article. 



