80 IMMUNE SERA 



increased by the immunizing process. The increase 

 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 complement 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. Of this freshly drawn serum 0.05 c.c. suf- 

 fice to dissolve 5.0 c.c. of a 5% mixture of ox 

 blood. If now we add to this haemolytic 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 addi- 

 tion 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 



