THE MANIFESTATIONS OF LIFE 83 



When we inquire into the meaning of the continuous 

 activity of normal life, as contrasted with the temporarily 

 suspended activity of fatigue and the permanently 

 suspended activity of death, we find it explainable 

 through a study of the nutritive or self-sustaining power 

 of the organism. 



Ordinary activity, exaggerated activity, exhausting 

 and fatal activity, being followed by varying degrees of 

 molecular disturbance through combustion, necessitate 

 varying degrees of molecular reintegraticm; i.e., the 

 introduction of new matter to replace what has been lost. 



Such new matter constitutes the food of the organism. 

 A food may therefore be denned as any substance 

 from which a living organism is able to derive material 

 for its sustenance or increase. 



It is a common observation that organisms beginning 

 their life histories as microscopic masses of protoplasm 

 eventuate in enormous numbers of simple or in enormous 

 masses of complex kind. Increase in size is known as 

 growth; increase in number, as reproduction. Such increase 

 of numbers or size being possible only through increase in 

 the actual quantity of the living substance, it becomes clear 

 that that substance is endowed with the capacity of form- 

 ing more substance of its own kind. Metabolic activity 

 manifested by increase of the living substance is anabolic, 

 and takes place by chemical synthesis of molecular groups 

 to higher and higher compounds until protoplasm is 

 reached. Metabolic activity manifested by the analysis, 

 by oxidation, of the already formed protoplasm, is said to 

 be katabolic, and results in the liberation of the potential 

 energy in the form of force and heat. In plants anabolism 

 preponderates ;_ in animals katabolism preponderates. 

 The explanation is found in the inactivity of plants as 

 compared with animals. 



Living substance or protoplasm is the most complexly 

 compounded of all the substances known to the chemist. 

 Indeed it is so complex in chemical structure that its 

 exact composition is unknown and no correct formula 

 for it has been worked out. 



