H^EMOLYSINS. 17 



may have a hundred times the amount necessary 

 for their solution. 



On What the Specificity Depends. From the pre- 

 ceding it follows that the specific action of the 

 haemolytic sera, and, I may at once add, of the bac- 

 tericidal sera also, is due exclusively to the immune 

 body. This possesses a combining group which is 

 specific for the cells with which the animal was 

 treated; e.g., the combining group of an immune 

 body produced by treatment with rabbit blood 

 will fit only to a certain group in the blood-cells of 

 rabbits; an immune body produced by treatment 

 with chicken blood will fit only to parts of the red 

 cells of chickens; one produced by treating an ani- 

 mal with cholera bacilli will fit only to this species 

 of bacteria and combine only with the members of 

 it. Keeping to the well-known simile of Emil 

 Fischer, the relation is like that between lock and 

 key, each lock being fitted only by a particular 

 key. 



To repeat for the point is of the greatest im- 

 portance the role of the immune body consists in 

 tying the complements of normal serum, which 

 have no affinity for the red cells or for the bacteria, 

 indirectly to these cells so that their solution and 

 digestion may be effected by the complements. 

 In other words, the immune body serves to con- 

 centrate on the corpuscular element to be dis- 

 solved all the widely distributed complement found 

 in normal serum. 



