THEORIES OF IMMUNITY. 



deprived of their toxines; that the phagocytes 

 contain the bactericidal cytases and produce the 

 fixatives; that the phagocytes absorb the toxic 

 substances. The great contradiction between the 

 occurrence of the bactericidal property and the 

 non-occurrence of immunity is to be explained by 

 the fact that the bactericidal substances in the 

 living tissues remain in the leucocytes and do not 

 escape except when the cells have received some 

 injury. The fact brought out by Gengou, that 

 the blood plasma has no bactericidal property, 

 has given the " coup de grace " to the bacteri- 

 cidal theory of the body fluids. 



This work of Gengou (Ann. de l'Inst. Past., 

 1901, T. XV., p. 231) is one of the strongest 

 supports of Metchnikoff's theory. In it he at- 

 tempted to determine whether the properties of 

 the shed blood are actually the same as those of 

 the blood in the body. The general results 

 were of great importance in showing that in 

 blood received under conditions preventing the 

 appearance of coagulation there would appear 

 no, or almost no, bactericidal properties, while 



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