THEORIES OF IMMUNITY. 



body binds the two to the blood cells — thus al- 

 lowing the L atom group of the complement to 

 exert its destructive (lytic) action. 



For the production of the hemolytic property 

 (blood immunity it may be called), there are 

 required : 



1. The blood cells that are injected. 



2. The body cells in the animal into which 

 the above are injected. 



3. Complement (present in fresh serum.) 

 The molecules of each of these and their re- 

 action upon each other may be shown thus : 



1. The blood cell molecule=H+N+X 



2. The body cell " ^H-f-^T+N+X 



3. Complement, =//+L+X 



As in the preceding case, the H group of the 

 complement is bound to the body cell by the cor- 

 responding H group, the blood cell by another. 

 The H groups of the body cell are needed for its 

 ordinary metabolism, but are taken up in this 

 way ; if the cell is to live they must be repro- 

 duced ; as the cell does live they are reproduced, 

 and as is usual, this reproduction goes on to ex- 



75 



