232 THE PRESENT EVOLUTION OF MAN— PHYSICAL 



their environment which is caused by the presence of 

 this or that toxin, and that this adaption is more readily 

 achieved when it is accomplished by degrees — i. c. by a 

 series of efforts. 



Of course it is possible that skin-cells, muscle-cells, 

 nerve-cells, leucocytes, &c. become adapted to changes 

 in the environment through a process of Natural Selec- 

 tion, through the survival of the fittest among them, and 

 that they do not really react to stimulation, but that the 

 unfittest among them perish, leaving in each succeedincr 

 cell-generation the more and more fit to continue the 

 race — i. c. that they do not transmit acquired traits any 

 more than multicellular organisms do, but undergo evo- 

 lution only through the accumulation of inborn varia- 

 tions. But this also is highly improbable, since the 

 adaptive change is often accomplished in a time which 

 is apparently too short to admit of such evolution 

 among the cells ; for instance, it is hardly possible that 

 acquired immunity against small-pox is due to evolu- 

 tion among the phagocytes owing to the continued 

 survival of their fittest. On the other hand, it is 

 possible that this adaptive change in the cells is due 

 to the survival of the fittest among their biaphors ; that 

 is, to the survival of the fittest among those hypotheti- 

 cal units winch are supposed to stand in the same rela- 

 tion to the cell as the cell stands in relation to the 

 multicellular organism. 



