A GENERAL RESUME OF IMMUNITY. 509 



I believe this is owing to the fact that in interpreting experiments 

 insufficient attention was paid to two essential points, the first of 

 which is the antagonistic power of serum, and the other that a given 

 alexin does not destroy all cells with equal facility. Gay and I have 

 given over an entire article to the study of the antagonistic property 

 of serum, and have called attention to the fact (which was likewise 

 brought out by the researches of Muir and Browning in the same 

 direction) that blood corpuscles, particularly when feebly sensi- 

 tized, may remove only a small amount of the alexin from a sur- 

 rounding fluid, even when they are present in large numbers. The 

 same idea applies, of course, to bacteria. Such a fact destroys 

 all the value of the so-called "elective complement absorption 

 method." The fact that in the presence of a sensitized cell a cer- 

 tain portion of the alexin may remain free in the surrounding fluid 

 does not in any way prove that this non-absorbed alexin differs from 

 that which has been fixed. This remark also applies to experiments 

 in which weakly sensitizing sera are used (normal sera for example), 

 experiments that have been frequently used to demonstrate a func- 

 tional multiplicity of the alexin. 



In the second place, when we note that a small dose of a given 

 alexic serum suffices to destroy sensitised corpuscles of species A, 

 whereas a larger amount of the same serum is necessary to destroy 

 sensitized corpuscles B, we are not authorized to conclude that two 

 different alexins are present, each one appropriate for only one 

 of these two species of corpuscles, and that one of these alexins 

 exists in larger amount than the other. In accordance with the 

 work of Muir and Browning, and of Gay especially, we must con- 

 clude that there is only one alexin, but that corpuscles differ in the 

 amount of this substance which they require for hemolysis. 



It is further to be noted that the partisans of a functional multi- 

 plicity of the alexin have since modified their original conception to 

 a great extent. They now admit that various amboceptors from a 

 given animal species have a uniform structure in so far as the com- 

 plementophilic group is concerned, which is equivalent to saying that 

 they absorb the same alexin. If we are to admit, then, that various 

 hemolytic or bacteriolytic sensitizers produce fixation of the same 

 alexin on various cells which they affect, we evidently admit that 

 these alexins may be used indifferently in hemolysis and bacterioly- 



