THEORIES OF IMMUNITY. 



protecting the body against the attacks of the 

 spores, and on the other the spores overcame 

 the action of the leucocytes and overwhelmed 

 the tissues. (Yirch. Arch., 1884, T. XCYL, p. 

 177.) Some time after this he published his 

 work on anthrax (Ibid., 1884, T. XCVL, p. 

 502), in which he demonstrated in the case of 

 the vertebrates, also, that the bacteria penetrated 

 the cells and set up a definite reaction between 

 themselves and these cells. 



As a result of these investigations, Metch- 

 nikoff elaborated his theory of phagocytosis 

 against bacterial invasion — based upon the 

 power of the ameboid cells to seize upon and de- 

 stroy bacterial cells, thus preventing them from 

 developing and injuring the tissues. 



He goes on to say (I. c.) that he had sup- 

 posed that the facts of absorption and in regard 

 to the leucocytes already accumulated would 

 lead the pathologists to look favorably upon the 

 theory that these leucocytes were active de- 

 fenders of the system against the attacks of the 

 bacteria. This, however, was far from being the 



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