J4 8 APPENDIX. 



loses its solvent power by exposure to heat, say to 

 55 C. Investigations showed that the solvent 

 action could be restored to these sera by the addi- 

 tion of small quantities of a fresh normal serum, 

 i.e. of a serum which by itself had no solvent power 

 whatever. The inactive serum had thus been 

 reactivated. The original specific dissolving serum 

 therefore contained two substances, one of which 

 is very labile and the other stable. The stable 

 substance is specific for the blood cells against 

 which it is directed, i.e. against the cells used for 

 immunizing the animal. It is called the " immune 

 body," or the "amboceptor." The labile sub- 

 stance, as we have seen, is present in all fresh sera, 

 and is spoken of as the " complement." The action 

 of the immune body seems to consist in bringing 

 the solvent action of the complement to bear on 

 the given cells. We must conceive that the com- 

 plement possesses the solvent power, but has no 

 way of laying hold of the cell to be dissolved. The 

 immune body merely effects this combination. 

 Ehrlich's diagram on page 64 will serve to make 

 this conception clear. 



All that has been said regarding immune bodies 

 and complement for the solution of blood cells, 

 holds for the substances which effect destruction of 

 bacteria when bacteria are used for immunization. 

 In fact, the process is the same, no matter what 

 cells are injected into the animal. The immune 

 body is always directed specifically against the 

 cells injected, and against no others. 



