THEORIES OF IMMUNITY. 



normal serum, and may be destroyed by heating 

 to 55° C. for half an hour; its presence is 

 demonstrated by such an occurrence as that 

 above mentioned, in which the hemolytic power 

 returns after the addition of a little fresh serum, 

 not of itself possessing the lytic property. This 

 substance (in the fresh serum) is called " com- 

 plement " by Ehrlich (also " addiment "), and is 

 the alexine of Bordet, Metchnikoif, and other 

 writers; it is probably also the same as the 

 " alexine " of Buchner, although there seem to be 

 some minor differences in the thought in regard 

 to their identity. 



The second substance exists in the serum of 

 an animal subjected to the process of immun- 

 ization, and can be destroyed by being subjected 

 to heat at 75° C, for one-half hour. To this 

 substance Ehrlich has given the name " immune 

 body." It corresponds as nearly as may be 

 to the " substance sensibilisatrice " of French 

 writers and supporters of the cellular theory of 

 immunity. 



In order to develop his theory of chemical 

 action in explanation of the condition of immu- 



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