THEORIES OF IMMUNITY. 



IV. 



SUMMARY. 



A study of the present position of the two 

 main theories explanatory of immunity shows 

 that they are not so far apart as is generally 

 supposed. 



Both sides agree that the phenomena seen in 

 active immunity require two substances (immune 

 body or substance sensibilisatrice, and comple- 

 ment or alexine). 



One side, however, insists that these sub- 

 stances remain in the cells (phagocytes). The 

 other maintains that they exist in the blood 

 stream (although, as has been seen, cell activity 

 is necessary for the production of the immune 

 body, at least). This latter fact of itself pro- 

 hibits the belief in a purely humoral explanation 

 of immunity. 



Both sides agree that ;r immune body " (sub- 

 stance sensibilisatrice) varies, is multiple and 



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