AMBOCEPTOR, COMPLEMENT, AND ANTICOMPLEMENT. 263 



A priori, it is, of course, conceivable that in the rabbit the 

 complements A\ and B\ exist exactly in the same proportion as do 

 complements A and B in the guinea-pig, but we must admit that 

 this would be a coincidence. In all probability the development 

 of the alloiogenic anticomplement will result in a serum in which the 

 proportion of the two anticomplements is absolutely different, so 

 that, for example, anticomplement B will be present in much smaller 

 amount than in the isogenic anticomplement serum. The behavior 

 of this will then be as follows: A certain quantity of the isogenic 

 anticomplement serum produced by guinea-pig serum (presupposing 

 that its constitution is uniform) will neutralize guinea-pig serum in 

 such a way that complement A and complement B of this mixture 

 are neutralized at the same time. If we proceed to do the same 

 with the alloiogenic anticomplement serum, we find that in the mix- 

 ture of anticomplement and guinea-pig serum, complement A is 

 completely neutralized, but that a larger or smaller excess of com- 

 plement B is still unsaturated. In those cases in which comple- 

 ment A is the dominant complement both mixtures will prove neutral; 

 when amboceptors are employed for which B is the dominant com- 

 plement, only one of the mixtures will be neutral, the other will still 

 be active. 



Now we shall assume that with the employment of large amounts 

 of amboceptor, a partial amboceptor comes into action which is 

 present in the immune serum in relatively small quantity. This partial 

 amboceptor is complemented by complement B contained in guinea-pig 

 serum, whereas the preponderating amboceptor is sensitized by comple- 

 ment A. Complement B finds a plentiful amount of anticomple- 

 ment in the isogenic immune serum, but not in the alloiogenic serum. 

 In the latter case, therefore, disproportionately much serum contain- 

 ing B anticomplement will be required in order to inhibit the com- 

 plement action when large quantities of amboceptor are present. If 

 the difference becomes so great that the anticomplement against 

 complement B is present only in very slight amounts, we shall have 

 a condition like that described by Marshall and Morgenroth (see 

 page 222). They found an ascitic fluid which was effective only 

 against a particular complement of a serum, while it was entirely 

 inert against another serum of this same species. 



We have endeavored to establish this point of view on a wider 

 experimental basis. With this end in view we first used small amounts 

 of amboceptor, adding various multiples of the complementing dose 



