NUTRITION. 



203 



containing waste). But experiment shows that increased 

 muscular action, such as mountain climbing, hardly in- 

 creases the amount of urea excreted. Such work, how- 

 ever, does largely increase the amount of carbon dioxid 

 excreted. It is thought, therefore, that our energy is 

 largely derived from carbohydrate foods and fats, and this 

 view is strengthened by the fact that our beasts of burden 

 depend chiefly on carbohydrate foods. 



ASSIMILATION^, 

 CIRCULVTION, 



ABSORPTION^ 

 DIGESTION 



VEGETABLE FOOD 



INORGANIC (MINERAL) MATTER 



Fig. 75. Life Processes. 



While increased muscular action does not very per- 

 ceptibly increase the amount of urea excreted, an addition 

 to the amount of proteid food taken does increase the 

 amount of urea. 



Metabolism. The building-up or constructive pro- 

 cesses are included under anabolism, while katabolism 

 designates the tearing down or destructive processes. All 

 the processes of nutrition, both of building up and tearing 

 down, are included in the term metabolism. 



The Indestructibility of Matter. We are agreed that 

 we cannot destroy matter. We may demolish a house, but 

 the material is all there. We may burn it, but if we could 

 gather the ashes and that part of the smoke and gases 



