INFECTION AND IMMUNITY. 607 



the immediate destructive activity of its "zymotoxic" 

 group. 



It is interesting to note in connection with this 

 hypothesis, that both " receptors " and " complements " 

 are present in normal susceptible, as well as in immune 

 animals, but that during immunization only the "recep- N / / 

 tors " are multiplied as a result of the specific stimula- 

 tion necessary to the establishment of immunity. 



THE ORIGIN OF COMPLEMENT. The origin of com- 

 plement is a question that is still unsolved. Some 

 investigators are inclined to believe that it is derived 

 from the leucocytes. This is the opinion of Metchnikoff 

 and his associates, while others believe that it is derived 

 from other cells and organs as well as from the leucocytes. 

 Again other investigators believe that it is not derived 

 from the leucocytes at all, but from certain other organ 

 cells, for instance, the spleen, pancreas, liver, and the 

 bone marrow. It is impossible with the knowledge at 

 hand at the present time to state definitely the origin of 

 the complement. 



Multiplicity of Complement. Ehrlich and his associates 

 have demonstrated that in normal serum several comple- 

 ments occur in association. These complements appar- \/ 

 ently have somewhat different functions, as indicated by 

 the influence upon blood serum when saturated with cer- 

 tain elements ; in this way removing one form of com- 

 plement, and leaving the others intact. Again, filtering 

 the serum through a porcelain filter, serves to separate 

 some complements and allows others to remain in the 

 serum. 



CONCLUSIONS. According to the nature of the intoxi- 

 cant from which the animal is immunized, the one or the 

 other of the structurally and functionally different types 



