638 COLLECTED STUDIES IN IMMUNITY. 



The other amboceptor is present in much smaller amount, and is the 

 amboceptor for which the horse complement is dominant. This 

 explains how a small amount of amboceptor binds complement, and 

 how haemolysis is effected only with a considerable excess of immune 

 serum. The relations existing between weak and strong concen- 

 tration of amboceptor in the immune serum are to a certain extent 

 analogous to those existing between horse and ox amboceptor in the 

 haemolysis of guinea-pig blood. There is, however, an important 

 difference. In the haemolysis of guinea-pig blood the affinity of the 

 ox amboceptor to the horse complement exceeds that of the horse 

 amboceptor. When both amboceptors are present, therefore, 

 haemolysis occurs. In the haemolysis of the prepared ox blood, 

 however, it is not sufficient that both amboceptors are present, for 

 under these circumstances, apparently, the complement is still 

 anchored by the amboceptor for which it is not dominant. In order 

 that the complement may lay hold of the other amboceptor, the 

 cooperation of the inactive ox serum is necessary. This serum, as we 

 have seen, must have direct relations with the horse serum. The 

 only way in which we can conceive of this relation is to assume 

 that the ox serum binds a horse serum constituent of complement 

 character which directs the effective horse complement toward the 

 amboceptor unsuited for producing haemolysis. The principle 

 underlying this explanation is not new, similar relations having been 

 studied by Ehrlich and Marshall. 1 In a combination described by 

 these authors, it was shown that the union of a certain non-dominant 

 complement did not occur until after another complementophile 

 group of the amboceptor had bound the particular complement 

 which was dominant in this case. It is possible that we are here 

 dealing with an analogous phenomenon. 



If we succeed, therefore, in removing the constituent of horse 

 serum which causes the effective horse complement to combine with 

 the unsuited amboceptor (and this, as we have seen, is accom- 

 plished by the action of ox serum) , we permit the horse complement 

 to unite with the other, effective, amboceptor and haemolysis can 

 occur. In this case, however, it follows that the binding of the horse 

 complement to the weakly prepared ox blood will not occur if the 

 horse serum constituent which brings about this binding is rendered 



1 Ehrlich and Marshall, Berliner klin. Wochenschrift, No. 25, 1902. See 

 also this volume, page 226. 



