608 COLLECTED STUDIES IN IMMUNITY. 



A number of observations made during the course of other experi- 

 ments gives additional support to the view that the inhibiting 

 action is due to anticomplements whose action is hidden, in native 

 sreum, by the normal amboceptors. Thus, it was possible to bring 

 about inhibition by absorption, only when the serum employed 

 already contained amboceptors for the blood-cells in question. 

 Where these- amboceptors were absent, no change whatever was 

 produced by the absorption, the serum either inhibiting equally 

 well before and after absorption, or not inhibiting at all. Normal 

 rabbit serum, for example, is in no way changed when absorbed 

 with ox blood-cells, because it lacks fitting receptors for these cells. 

 Owing to the fact, however, that it contains anticomplements, 

 rabbit serum even in its native state exerts an antilytic effect on 

 ox-blood haemolysis, and this action is unaffected by absorption 

 either with ox blood or sheep blood. In this connection the indi- 

 vidual variations observed in the behavior of rabbit sera toward 

 sheep blood is most instructive. Thus, I have encountered rabbit 

 sera in which, by chance, the amboceptors for sheep blood were 

 practically absent. These sera, however, even in the native state, 

 possessed an antilytic effect on sheep-blood haemolysis, and this 

 was unaffected by treatment with sheep blood-cells. 



Finally mention should be made of a circumstance which makes 

 it highly probable that the substances in question are anticomple- 

 ments. We have seen that the inhibiting serum produces its effect 

 when guinea-pig serum is used as complement. On the other hand, 

 no inhibition will be produced if rabbit serum is used as comple- 

 ment. The amboceptors present are complemented with rabbit 

 serum just as well as with guinea-pig serum, and the failure of 

 absorbed rabbit serum to inhibit when rabbit serum is used as com- 

 plement can be readily understood if we regard the inhibition as 

 due to anticomplements as already set forth, for it is well known 

 that autoanticomplements are uncommon. 



It is, of course, impossible for us to say whether the data here 

 reported are applicable to the observations made by Pfeiffer and 

 Friedberger on bacteria. From what has been said it is apparent 

 that the specificity observed by those authors would agree very 

 well with the anticomplemenjb hypothesis. Nor is this hypothesis 

 contradicted by the fact that a certain excess of amboceptor nullifies 

 the paralyzing action of the inhibiting serum. In anticomple- 

 ment actions the quantitative relations between amboceptor, 



