THE CELL AND PROTOPLASM. 71 



activities. Why is it that the oxidation of 

 starch in the living machine gives rise to motion, 

 growth, and reproduction, while if the oxidation 

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

 bit of dead protoplasm, it simply gives rise to 

 heat 1 ? 



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 

 mechanical 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 



