THEORIES OF IMMUNITY. 



metabolism of the tissue cells in which the injec- 

 tion is made are used for another purpose — 

 these are reproduced in excess, and cast off into 

 the blood stream, where they exist as substances 

 capable of aiding in the cytolytic action. 



Both sides, that which supports the "humoral" 

 and that supporting the " cellular " theory, agree 

 in supposing that two bodies are necessary for 

 the production of these reactions, but there 

 are two special points of dispute — first as to 

 whether the complement exists in the cells or out 

 of them; and second, whether it is single and 

 specific for the race of animals in which it occurs, 

 or whether it is multiple and specific only for 

 the reaction in which it appears active. 



There is no dispute as to the complexity or 

 rather multiplicity of the immune bodies, which 

 are generally acknowledged to be very numerous 

 and capable of action only in special directions 

 — on the particular bacteria or tissue cells, as the 

 case may be. 



As to the multiplicity of complement, it has 

 been shown that it is possible to reactivate a 

 serum by the addition of a little fresh serum 



80 



