84 THE NATURE AND ORIGIN OF LIFE 



certain point of view, the law of assimilation might seem 

 exact enough. 



It is no longer the same thing when we use the injected 

 colloid as a reagent. Then we can always verify that the 

 animal has undergone a modification with reference to the 

 nature itself of the colloid, a modification which is so specific 

 with reference to this colloid that it is commonly irresponsive 

 to any other colloid. 



A few examples are needed to establish so general a law, 

 which seems, at first sight, to put aside and finally to con- 

 demn the law of assimilation pure and simple. 



Sheep Anthrax 



A first example may be taken from the history of the 

 sheep cured of anthrax. This sheep, inoculated with anthrax 

 bacteridia, was diseased (the period of struggle against the 

 microbe we call disease). But, at last, after several days, 

 all the bacteridia with which it had been inoculated disap- 

 peared from its interior medium. Now they had not been 

 eliminated by the kidneys or other organs of excretion care 

 was taken in the laboratories to make sure of this. There- 

 fore they were killed and assimilated by the sheep, for which 

 they served as a food a food not agreeable, dangerous 

 even, but, in spite of all, a food, since the bacteridia were 

 transformed into the substance of the sheep. 



But after the cure, in spite of appearances, the sheep is 

 not what it was before ; it has become refractory to anthrax. 

 If after a certain time you inoculate it again with anthrax 

 bacteridia, it will not get sick as before ; it will assimilate 

 the bacteridia and not be troubled by them. Now it is 

 Only with reference to anthrax bacteridia that it has acquired 

 such immunity. It is still liable to any other disease what- 

 soever that is peculiar to the species sheep. This fact may 



