84 PROPERTIES OF ILEMOLYTIC SERA 



them by an immune-body. But, in addition, there is, 

 unlike the two previous cases, a deficiency also in the com- 

 bining power of complement beyond a certain point, or, in 

 other words, only a small proportion of the molecules of 

 the red corpuscles combined with immune-body (R + IB 

 molecules) take up ox's complement. 



The fact that in the case just described, only some of 

 the R + IB molecules take up complement is of considerable 

 theoretical importance. It is to be noted that almost all 

 the R -[- IB molecules capable of taking up complement are 

 present after the addition of one dose of immune-body, 

 and that the subsequent addition of the same immune- 

 body molecules scarcely increases the amount of comple- 

 ment taken up, though these molecules combine with the 

 receptors of the red corpuscles. It would therefore appear 

 that the failure on the part of an R + IB molecule to combine 

 with complement is due in some way to the receptors and 

 not to the immune-body. According to Ehrlich's theory 

 the amboceptor (immune-body) has practically no affinity 

 for complement in the free state, but acquires that affinity 

 when combined with the tissue or bacterial molecule. But 

 the result above stated would, according to .the amboceptor 

 hypothesis, imply that only some molecules capable of 

 combining with immune-body give the latter affinity for 

 complement. According to the view that the immune- 

 body renders the tissue molecule capable of taking up com- 

 plement, the explanation would simply be that some of 

 the molecules of the ox's corpuscles have no combining-group 

 for the ox's complement, though they enter into combina- 

 tion with immune-body. It is not possible on theoretical 

 grounds to establish either of these hypotheses by the 

 exclusion of the other, but whichever may be ultimately 

 established, the importance of the nature of the tissue 

 molecule or receptor in determining whether complement 

 will be taken up or not is brought out with sufficient clearness. 



