PHENOMENA OF LIFE 23 



a changeable substance should possess great specificity, yet such 

 is the case. The protoplasm of each species of organism is per- 

 fectly distinct from that of every other species. A tree of a 

 certain variety always gives rise to other trees similar to it ; 

 for example, a pear seed never develops into a peach tree, 

 but always into a pear tree of the same kind that produced it; 

 likewise the egg of a pure-bred Plymouth Rock hen never gives 

 rise to anything but a chicken of the Plymouth Rock variety. 

 Nevertheless, both the tree and the hen take their origin from 

 an apparently simple microscopic bit of protoplasm, the fertilized 

 germ cell. 



5. A PHYSICO-CHEMICAL EXPLANATION OF THE PHENOMENA 

 OF LIFE 



The efforts of the alchemist of old who wrought in the seclusion 

 of his laboratory were directed toward the solution of two prob- 

 lems: the production of an elixir of life, and the manufacture of 

 gold. His time has passed, and his problems were never solved. 

 His successor of modern times, the biochemist, has likewise 

 chosen problems of fundamental importance and great difficulty; 

 he has attempted to give an explanation of all vital phenomena 

 by means of physical and chemical laws. The scientific world 

 now contains many scholars who maintain that living organisms 

 are really machines, and are opposed to the idea of vitalism, which 

 presupposes the presence of some vital principle. One of the 

 leading investigators in this field claims that living organisms are 

 to be considered as "chemical machines, consisting essentially 

 of colloidal material, which possess the peculiarities of auto- 

 matically developing, preserving, and reproducing themselves " 

 (15, p. i). Another prominent zoologist makes the following 

 statement: " I say again, with all possible emphasis, that the 

 mechanistic hypothesis or machine theory of living beings is not 

 fully established, that it may not be adequate or even true; yet I 

 can only believe that until every other possibility has really been 



