CHAPTER V 



THE SOURCES OF FOOD 



WE have not yet considered all the known modes 

 of nutrition for it will be more convenient to discuss 

 some of them when dealing with the question of the 

 circulation of food-stuff in the sea. We shall not be 

 able to understand the meaning of the more obscure 

 modes of nutrition unless we have clear ideas as to 

 the assimilation of food. All organisms, whatever be 

 their mode of life, have this in common, that their 

 bioplasm continually wastes away by its own activity 

 and must be renewed ; and further, to obtain energy all 

 must oxidise or transform some substance which the 

 bioplasm associates with itself. The substance which 

 they use in order to renew their bioplasm is proteid, 

 and that which they use to obtain energy is called 

 the respirable material. The latter may be one of 

 several substances. 



In green plants and animals the respirable 

 material is some form of fat or carbohydrate, and 



