THE CELL AND PROTOPLASM. 57 



occurs in the chemist's laboratory, or even in a bit 

 of dead protoplasm, it simply gives rise to heat ? 



One of the primary questions to demand atten- 

 tion in this search is whether we are to find the 

 explanation, at the bottom, a chemical or a mechani- 

 cal one. In the simplest form of life in which vital 

 manifestations are found are we to attribute these 

 properties simply to chemical forces of the living 

 substance, or must we here too attribute them to 

 the action of a complicated machinery ? This 

 question is more than a formal one. That it is 

 one of most profound significance will appear 

 from the following considerations : 



Chemical affinity is a well recognized force. 

 Under the action of this force chemical com- 

 pounds are produced and different compounds 

 formed under different conditions. The proper- 

 ties of the different compounds differ with their 

 composition, and the more complex are the com- 

 pounds the more varied their properties. Now it 

 might be assumed as an hypothesis that there 

 could be a chemical compound so complex as to 

 possess, among other properties, that of causing 

 the oxidation of food to occur in such 'a way as 

 to produce assimilation and growth. Such a com- 

 pound would, of course, be alive, and it would be 

 just as true that its power of assimilating food 

 would be one of its physical properties as it is 

 that freezing is a physical property of water. If 

 such an hypothesis should prove to be the true 

 one, then the problem of explaining life would 

 be a chemical one, for all vital properties would 

 be reducible to the properties of a chemical com- 

 pound. It would then only be necessary to show 

 how such a compound came into existence and 

 we should have explained life. Nor would this 



