40 FUNDAMENTAL PRINCIPLES 



66. Metabolism the Central Fact in Life. — All life activities result 

 from metabolism in the living organism, and therefore life might be 

 defined as the orderly series of metabolic changes which occur in matter 

 possessing the necessary protoplasmic organization. In last analysis all 

 of the functions of the living body may be described in terms of metabo- 

 lism. The animal organism may be conceived as an energy system, and 

 it has also been likened to a chemical machine the product of which is 

 kinetic energy. The plant organism, likewise, may be conceived as an 

 energy system and as a chemical machine, but its product is largely 

 the complex organic compounds which form the basis of the food of 

 animals. 



