METHODS 



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first benign attack of anthrax can victoriously resist a second 

 inoculation of bacteridia more virulent than the first. It 

 issues from this second battle more hardened than before 

 and, at last, it will be able to resist an inoculation of the 

 most virulent bacteridia we can produce after they have 

 successively conquered non-refractory sheep. 



Here there is but a single sheep the same sheep which, 

 attacked by bacteridia more and more virulent and triumph- 

 ing over them successively, has become better able to resist 

 even the most virulent bacteridia in existence. Here, then, 

 must be an instance of personal adaptation for the struggle 

 against bacteridia. We cannot look on the refractory sheep 

 as one chosen out after the fact from the great number 

 of sheep, of whom some, in the chances of variation, were 

 found less fit to resist anthrax and so died under the repeated 

 attack of the bacteridia, whereas this one which the chances 

 of variation rendered fit to resist survived. Not only this 

 way of looking at things is inadmissible in the case, since 

 there is but a single sheep concerned in it, but we can see 

 how improbable also it would be, even in the case of several 

 sheep, because of the precise character of immunity with re- 

 gard to anthrax. There are just as many special immunities 

 as there are different microbian maladies ; and we should 

 have to admit that chance always gives certain sheep just 

 those precise qualities. 



We can get out of this difficulty, and keep to the Darwinian 

 explanation, by considering the sheep, not as a single and 

 indivisible individual, but as an aggregate of cells, each of 

 which can be studied in the language we have used for 

 the bacteridia. The struggle will then no longer be localized 

 between sheep and microbe, but between the cells of the 

 sheep and the unicellular microbes inhabiting it. In this 

 case, if we suppose all the cells of the sheep to be, like the 



