METHODS 87 



This protean mechanism the bacteridium or any living 

 cell which continues to live directs all its activity against 

 the exterior conditions of its environment. When it finds 

 itself in the interior of a sheep, it directs its struggle against 

 the sheep ; it has become a definite mechanism a bac- 

 teridium struggling against a sheep and thus differs from 

 that other definite mechanism a bacteridium struggling 

 against a phenicated bouillon. 



Here we come to the delicate part of the exposition of 

 this fundamental question. 



Suppose some scholar endowed with knowledge wanting 

 to us were able to verify completely, at any given moment, 

 the entire structure, colloid and chemical, of a bacteridium 

 considered precisely at that moment. The mechanism 

 cannot be compared to that of a locomotive ; for the latter, 

 when it works, works always the same. In this bacteridium, 

 on the contrary, a great number of mechanisms may be 

 verified, a great number of functions are possible. These 

 functions are not determined beforehand in the structure of 

 the bacteridium ; they can be determined only by the sum 

 total B of the exterior circumstances which intervene in 

 its working. In other words, take two anthrax bacteridia 

 identically the same from every point of view at a given 

 moment and with each of them I can realize a different 

 mechanism by steeping the first in a phenicated bouillon 

 and by inoculating a sheep with the second. In fact, the 

 two mechanisms (Bacteridium x Phenicated Bouillon) 

 and (Bacteridium x Sheep) have descendants that differ. 

 Those of the phenicated bouillon undergo certain variations 

 which we can scarcely appreciate directly, since the bacteri- 

 dium never habituates itself completely to the phenicated 

 bouillon ; but the variations, if we stop the experiment 

 soon enough, show themselves by a diminution of virulence 



