172 NUTRITION, DIETETICS AND ANIMAL HEAT 



Metabolism. By metabolism is meant those processes in 

 the body whereby food products are appropriated, their 

 stored-up energy utilized, and the waste discarded. 



Metabolism is divided into, (i) anabolism, and (2) kata- 

 bolism. Anabolism is the process of building up tissue by 

 cell appropriation of food stuffs. Katabolism is the process 

 of destroying tissue in order to set free energy that the or- 

 gans of the body may perform their various functions. 



When the anabolic processes are equal to the katabolic 

 there is no excessive storage of material, but an individual 

 remains of uniform size, weight, and strength. If the ana- 

 bolic are in excess of the katabolic processes, the excessive 

 products are stored up in cells and an individual increases in 

 size, weight and strength. If the katabolic processes are in 

 excess of the anabolic there is a call on the tissues for the 

 matter already stored there and there is a decrease in 

 strength, weight and size. 



Death. As long as a cell appropriates enough to supply 

 the deficit caused by the destruction of material in the ex- 

 penditure of energy, the cell will live; but when the intake 

 cannot make up for the output lost the cell ceases to func- 

 tionate and this is called death. 



Problems Involved in the Nutritive Process. Since the 

 actual changes occurring and the method of their produc- 

 tion cannot be understood, the question of nutrition resolves 

 itself into a consideration of the final fate of the various 

 aliments, of their relative value in nutrition, of conditions in- 

 fluencing the process, and of the explanation of certain 

 facts connected with the destruction of the food stuffs, par- 

 ticularly the production of heat. 



The change which the foods finally undergo in the body 

 is one of oxidation. It is therefore chemical changes which 

 give rise to physical activity. Oxidation is accompanied by 

 the production of heat. The same sum total of heat is de- 

 veloped when a piece of iron rusts completely away in five 

 years as when it is consumed in an atmosphere of oxygen in 



