WASTE IN FUNCTIONAL METABOLISM 81 



in the food do not correspond exactly with the substances 

 of which they are to make their protoplasm, they will 

 have to pick and choose the things which they can use 

 and reject the balance. This gives rise to an accumula- 

 tion of unused materials in connection with growth. 

 Some of these may be serviceable in connection with 

 basic or functional metabolism, others may be wholly 

 wasted. Growing boys often eat as much as twenty-five 

 pounds of food a week, although during that time they 

 may not gain more than a pound in weight, and their 

 combined basic and functional metabolism will not nearly 

 account for the other twenty-four pounds. The best way 

 to explain the great surplus of food which growing chil- 

 dren regularly eat is by supposing that the growth metab- 

 olism is wasteful, so that in putting together a pound 

 of body substance a good deal more than a pound of food 

 is required. 



Waste in Functional Metabolism. — As we have 

 already tried to make clear, the essential difference be- 

 tween functional metabolism and growth metabolism is 

 that in the former the liberation of energy is the import- 

 ant feature, a feature which is secured by the burning of 

 fuel. We are all familiar with the fact that wherever 

 fuel is burned waste products are formed. Since burning 

 is really the chemical process of oxidation, namely, the 

 combining of oxygen with food, there are bound to be 

 produced as a result of this combination substances of 

 which the energy value has been exhausted and which 

 are, therefore, from the standpoint of the tissues, waste 

 products. Chief among these is carbon-dioxid, one of 

 the materials which,, as we saw in an earlier chapter, 

 serves as the raw material for the manufacture of sugar. 

 Besides carbon dioxid, water, and various other less well- 

 known waste products are formed in connection with 

 functional metabolism. 



Waste Must Be Gotten Rid of if Metabolism is to 

 Continue. — The furnace fire cannot be kept going if 



