444 STUDIES IN IMMUNITY. 



is present in bovine serum a particular substance which is neither an 

 amboceptor, an agglutinin, nor an alexin, and which consequently 

 differs from the active substances that have been previously recog- 

 nized in studies on immunity. This substance has the property of 

 combining with corpuscles that have already been laden with sen- 

 sitizer and alexin, and this combination generally favors hemolysis. 



Two preliminary ideas are necessary in order that the facts may 

 be clearly understood. The first is that horse alexin is very weak 

 in so far as producing hemolysis is concerned. Corpuscles that have 

 been strongly sensitized by a heated immune serum show little or 

 no hemolysis on the addition of horse serum.* Consequently, 

 when horse alexin is used, an absence of hemolysis does not prove 

 that the corpuscles concerned are not sensitized, that is to say, 

 have not fixed the amboceptor. 



The second point is, that fresh horse serum contains a relatively 

 strong amboceptor for guinea-pig corpuscles which produces a good 

 alexin fixation. The fact, then, that fresh horse serum does not 

 destroy the corpuscles is not due to its lack of sensitizer, but be- 

 cause its alexin is incapable of hemolyzing. If this alexin is replaced 

 by another, for example, if fresh guinea-pig serum is added to the 

 mixture of guinea-pig corpuscles and horse serum, hemolysis takes 

 place. We are forced, then, to admit in Ehrlich and Sachs' experi- 

 ment, which consists in mixing fresh horse serum and heated bovine 

 serum with guinea-pig corpuscles, the presence of two amboceptors, 

 bovine and horse, both of which produce a sensitization, but 

 either one of which suffices to produce the result. Either one 

 of these amboceptors may indeed be used alone without changing 

 the result of the experiment. This fact, to be sure, is scarcely accept- 

 able to Ehrlich and Sachs, according to whom the amboceptor in 

 their experiment is furnished entirely by the bovine serum. And 

 when these authors find on treating bovine serum with guinea-pig 

 corpuscles that the serum still retains its property of rendering horse 

 serum hemolytic for new corpuscles, their conclusion is, as we have 

 seen, that the bovine amboceptor has remained free in spite of 

 contact with the corpuscles. 



* For example, bovine corpuscles sensitized by rabbit antibovine immune 

 serum. The hemolytic weakness of horse alexin is not the same with all species 

 of corpuscles. 



