CELLULAR THEORY OF IMMUNITY 317 



or else if they did have these powers, they were without 

 apparent relation to the resistant or vaccinated state 

 of the animal. For the conservation of immunity, the 

 same criticisms apply as to the theories of Pasteur and 

 Chauveau. A chemical action, whatever it may be, 

 cannot be lasting in an organism in which all the chemi- 

 cal elements are constantly being renewed. There is 

 only the cell which lasts, because it lives. It is more 

 likely that the explanation of immunity lies in the 

 cellular theories than in the humoral theories which we 

 have just briefly reviewed. 



X 



CELLULAR THEORY OF IMMUNITY 



Pasteur, who in his heart was indifferent to theories 

 and asked of them only that they suggest experiments 

 to him, held for a long time a purely cellular conception 

 of microbial disease. It was by a struggle between the 

 red blood corpuscles and the bacteridium that he ex- 

 plained in 1878 the resistance of the living fowl to anthrax, 

 and we see him at every instant, in that period, having 

 recourse to vital resistance, and saying: "Among the 

 lower forms of life, still more than in the higher species 

 of plants and animals, life prevents life." Again, it was 

 this same sentiment which guided him in the experiments 

 which we have seen him making, to prevent the develop- 

 ment of the anthrax bacteridium by inoculating at the 

 same time with some common bacteria. Pasteur, how- 

 ever, was conscious of not having laid hold of the vital 

 point of the mechanism of the resistance of the organism, 

 and it is perhaps for that reason that when he heard of 

 the researches of Metchnikoff on phagocytosis, he gave 



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