39 



munizing process. The""iiic Jea^eT affects solely the 

 immune body. It is therefore possible to have a 

 serum which contains more immune body than 

 complement to satisfy it, and if we withdraw such a 

 serum from an animal we shall find that it contains 

 some free immune body. This serum can only then 

 exert its full power when the full amount of comple- 

 ment is present, i.e., when some normal serum is 

 added. If we treat a rabbit with the red cells of an 

 ox, as v. Dungern did, we shall obtain a serum which 

 is haemolytic for ox blood. 0.05 c.c. of this freshly 

 drawn serum suffices to dissolve 5.0 c.c. of a 5% 

 mixture of ox blood. If now we add to this haemo- 

 lytic serum a little normal rabbit serum, we shall 

 find that only one-tenth of the amount of serum is 

 required; i.e., only 0.005 c - c - to dissolve the same 

 quantity of ox blood. This means that through 

 the addition of the rabbit serum, which, of course, 

 is not haemolytic for ox blood, a sufficient amount 

 of complement was added to enable all the immune 

 body of the specific serum to act. This specifically 

 increased power of the immune serum to act on 

 certain definite cells depends on the fact that the 

 immune body resulting from the immunizing 

 process concentrates the action of the comple- 

 ment scattered through the serum, on cells for 

 which it has definite affinities. If 2 c.c. of normal 

 guinea-pig serum are able to dissolve, we will say, 

 5 c.c. of a 5% defibrinated rabbit-blood mixture, 

 and if we find that after the immunizing process 



