THE MECHANISTIC CONCEPTION 21 



microscopical appearances within the egg during the 

 period of cell division are such as to suggest that quite 

 definite physicochemical processes have been set 

 in train by the action of the sperm. There are 

 numerous indications, which need not be put for- 

 ward, that specific enzymes are concerned in promi- 

 nent and even determining ways with the entire 

 mechanism of cell division. The very narrow limits 

 within which these processes of cell division occur 

 make it extremely difficult to investigate the chemi- 

 cal aspect of the problem. Yet even here there 

 are signs of progress, and it seems not unreasonable 

 to hope that human ingenuity will one day provide 

 the conditions for the serious study of the chemical 

 forces inseparably bound up with this problem. In 

 other words, we may say that despite our present 

 ignorance, the reproductive process in the cell shows 

 morphological and other signs of resting on physico- 

 chemical forces. How far these or other natural 

 forces will be shown to be responsible for cell divi- 

 sion no one can say, but it is reasonable to expect 

 great advances in the direction of an increasingly 

 refined and more adequate understanding of these 

 forces. 



A fourth distinctive feature of the animal organism 

 is its capacity to grow. A highly noteworthy thing 

 about this capacity to grow is the evidence of defi- 

 nite regulation of the growing parts. This regula- 

 tion is so orderly and precise as to excite wonder and 

 admiration. How does it happen that the various 



