THE SENSITIZERS OF SERA. 245 



alexin, no morphological change in the specific cell is necessary to 

 prove the existence of a sensitizer in a given serum. A disappear- 

 ance of the alexin from the fluid is the only essential criterion. By 

 this means Bordet and Gengou* were able to find sensitizers in 

 the majority of antimicrobial sera, as, for example, in the sera of 

 animals injected with B. pestis, the bacillus of swine plague, the 

 first anthrax vaccine, B. typhosus, B. proteus vulgaris, and in the 

 serum of convalescents from typhoid fever. If, for example, we put 

 the same amounts of plague bacilli suspended in salt solution, and 

 of alexin, in two tubes, and then add to the first a given dose of 

 normal horse serum heated to 55 degrees, and to the second the 

 same amount of heated serum from a horse vaccinated against B. 

 pestis, it will be found that sensitized rabbit corpuscles, subsequently 

 added, undergo complete hemolysis in the first tube, but remain 

 intact in the second. In other words, the alexin has remained free 

 in the first and disappeared in the second. Suitable controls show 

 that it is indeed the plague bacilli influenced by the preventive 

 serum that fix the alexin. 



The facts have not been questioned so far as we are aware; 

 Aschoff,! however, has recently criticised the method employed by 

 Bordet and Gengou on the ground that the production of hemolysis 

 does not necessarily indicate the absence of a sensitizer (probably 

 in a normal serum) ; for, as he says, " besides the alexins suitable 

 for bacteriolytic amboceptors there may be alexins fitted for hemo- 

 lytic amboceptors. " This is not the point at issue, for B. & G. have 

 not sought to establish that there is no sensitizer in normal serum, 

 but that there is one in immune serum. And, what is more, if 

 Aschoff believes in the existence of an antiplague sensitizer in 

 normal horse serum as well as in antiplague serum, how does he 

 explain that the latter fixes these "hemolytic alexins," whereas 

 the former does not? 



From this summary it is evident that hitherto sensitizers have 

 been demonstrated and studied only in such sera as act on definite 

 cells. We may go further and consider whether the substance 



* See p. 217. 



t Aschoff : Ehrlich's Seitkettentheorie und ihre Anwendung auf die kiinstlichen 

 Immunitatsprozesse. Zeitsch. f. allgem. Physiol., 1902, 3 Hft 1 ter Bd. p. 159. 



