CHAPTER X 



THE UTILISATION OF FOOD BY THE ANIMAL 



Food as a Source of Energy. Heat Value of various Foods. 

 Energy consumed in Digestion and Internal Work. 

 Maintenance Rations. Feeding for Rapid Work or Increase 

 of Weight. Amount of Food required for a given Amount 

 of Work. Nitrogenous Materials required to repair Tissue 

 Waste. Minimum of Protein necessary. 



So far, we have only discussed the composition of 

 various foods and the process of digestion by which 

 they reach the body ; it is now necessary to consider the 

 purposes which these foods serve, and their utilisation 

 within the body. We will begin by looking at foods 

 from the standpoint of energy : we have already 

 indicated that an animal is an organisation which has 

 to be continually fed with some external supply of 

 energy in order to maintain its warmth and its power 

 of doing work. It resembles water running down- 

 hill, in that when once started it runs on of itself; the 

 transformation of energy continues as long as the 

 material containing the energy is supplied, and during 

 the transformation there is a certain wastage through 

 change into low-grade, unusable forms of energy. The 

 food and the oxygen together contain stored-up energy ; 

 like a reservoir of water at the top of a hill, they will run 

 down into carbon dioxide and water, the energy being 

 liberated as heat, just as the water will have parted with 



185 



