METHODS 85 



be summed up as follows : the sheep has become habituated 

 to assimilating anthrax bacteridia ; and this special habit 

 expresses the modification wrought in the sheep by an 

 injection of anthrax bacteridia, which it resisted. 



Oftenest, if you select your sheep by chance and take 

 the anthrax bacteridia from the body of a sheep that died 

 of anthrax, the bacteridia with which the sheep is inoculated 

 kill it after a few days ; and then we can verify that the 

 bacteridia have multiplied beyond measure in the interior 

 medium of the sheep. In this case it is the bacteridia which, 

 developing at the expense of the sheep's substance, assimi- 

 late the sheep. 



Have they really and strictly assimilated the sheep's 

 substance ? Do they remain identically the same as they 

 were at the start ? For the most part we find that they 

 too have been modified and their modification relates to 

 sheep. We say that they have increased their virulence for 

 sheep. This means that they have become fitter to survive 

 and prosper in a new sheep and to kill it. The only case 

 in which they are not modified is when the bacteridia with 

 which the inoculation is made already have the maximum 

 virulence for sheep. In the same way, when the sheep 

 wins in the struggle, it possibly suffers no modification, that 

 is, if it already has the maximum immunity from anthrax. 

 There is a limit to acquired habit and when the limit is 

 reached, there is no longer room for further habituation. 1 



In both cases, when the sheep resists and when the 

 bacteridia win the day, we are concerned only with the 

 victor. It is only in the being which continues to live that 

 we can establish the general law of habit. 



The history of the struggle between anthrax and sheep 



1 Then, as we shall see, the law of assimilation pure and simple 

 becomes applicable. 



