SENSITIZING ANTIBODIES 281 



From this, Ehrlich concluded that complement did not directly 

 combine with the corpuscles, but did so through the intervention of 

 the immune body. This immune body, he reasoned, possessed two 

 distinct atom-groups or haptophores; one, the cytophile haptophore 

 group, with strong affinity for the red blood cell; the other, or 

 complementophile haptophore group, with weaker avidity for the 

 complement. Because of this double combining power, Ehrlich 

 speaks of the immune body as "amboceptor." These views are 

 graphically represented in Figs. 132 and 133. 



Thus, according to Ehrlich and his pupils the alexin, or comple- 

 ments, acts upon the antigen indirectly only through the "zwischen- 

 koerper" or "amboceptor. " These views of Ehrlich have been 

 described in more or less detail because they form an excellent 



Complement 



body 



Cell used 



FIG. 33. COMPLEMENT, AMBOCEPTOR OR IMMUNE BODY. AND ANTIGEN OR 

 IMMUNIZING SUBSTANCE. 



introduction to a study of these phenomena. We. do not believe, 

 however, that they are tenable at the present time. It was Bordet 

 particularly who has pointed out many of the uncertainties of the 

 amboceptor point of view. The only thing that we can say with 

 certainty is that alexin or complement do not go into union with 

 the unsensitized antigen, but that the action of the alexin upon 

 the antigen is made possible only by preliminary sensitization, or, 

 in other words, by union with the specific antibody. This complex 

 then is amenable to alexin action. It is neither necessary, nor is 

 it justifiable on the basis of experimental fact, to assume that the 

 sensitizing antibody is an amboceptor or a sort of bridge between 

 the antigen and the alexin. The difference is a fundamental one, 

 and all the facts are on the side of the Bordet view, as far as we 

 can see. It is better to refer to the substances involved as sensitizer 

 and alexin, instead of as amboceptor and complement. As we shall 



