CHAPTER IX 

 GENERAL METABOLISM 



Introduction 



Life consists physiologically of a transformation of 

 energy. Animals are dependent for their supply of energy 

 upon the potential energy present in the food, this being 

 derived in the first instance from the sun through the 

 anabohc processes characteristic of plant-hfe. The energy 

 thus presented to the animal is converted by it into a 

 form which consists physiologically of cell-activity, and 

 mechanically of work and heat. The extent of this trans- 

 formation and its relation to the degree of activity are 

 capable of estimation. The body, in other w^ords, may be 

 considered as a machine in which the energy supphed is 

 balanced by the energy liberated. 



But the body itself is not unaffected by the processes 

 of combustion w^hich take place within it. Cell-life involves 

 a constant wear and tear which has to be made good. 

 This process of disintegration and reconstruction, unlike 

 the transformation of energy, cannot be measured, nor is 

 its relation to cell-activity known. 



The food when it enters the body undergoes one of two 

 fates. In the first place it may serve merely as a supply 

 of energy; its destiny is oxidation, and any changes 

 which it may undergo other than oxidation are either for 

 the purpose of storage or of the nature of preparation for 

 combustion. In the second place the food may become a 

 part of the cell itself, an essential cog in the wheel, its 

 presence being necessary for the performance and for the 



146 



