Origin of Different Kinds of Adaptations 377 



of its use may be found to be a very simple phenomenon that 

 requires no special explanation at all to account for its exist- 

 ence in the individual, further than that the muscles are of 

 such a kind that this is a necessary physical result of their 

 action. But until we know more of the physiology in- 

 volved in the process, it is idle to speculate about the ori- 

 gin of the phenomenon. 



Reactions of the Organism to Poisons, etc. 



In this case also we meet with a number of responses for 

 whose origin we can give not the shadow of an explanation. 

 On the other hand, the cases are significant in so far as a 

 number of them show quite clearly that the response cannot 

 have been acquired through the experience of the organism, 

 or the selection of those individuals that have best resisted 

 the particular poison. This is true, because in a number of 

 cases the poison is a substance that the animal cannot possi- 

 bly have met with during the ordinary course of its life, or 

 of that of its ancestors. It may be argued, it is true, that 

 in the case of the poisons produced by certain bacteria the 

 power of resistance has been acquired through the survival 

 of the less susceptible, or more resistant, individuals. Im- 

 probable as this may be in some cases, it does not, even if 

 it were true, alter the real issue, for it can be shown, as has 

 just been said, that the same power of responding adaptively 

 is sometimes shown in cases of poisons that are new to the 

 animal. 



There is no question that different individuals respond in 

 very different degrees to these poisonous substances, and it 

 is easy to imagine in the case of contagious diseases that 

 a sort of selective process might go on that would bring 

 the race up to the highest point to which fluctuating varia- 

 tions could be carried, even to complete immunity ; but even 

 if this were the case, it seems to be true that the moment 



