FOODS IN NUTRITION 175 



nitrogenous supply which is built up into a part of the cell has 

 been called "tissue proteid" Whether any given molecule of 

 proteid food pass through the system as circulating or tissue 

 proteid is only an accident provided the supply be above the 

 demand of the cells for tissue proteid; these demands are the 

 first to be supplied by the nitrogenous material at hand. 



From this it is not to be inferred that the exigencies of nutrition 

 will be met as well without as with circulating proteid. When 

 the diet consists of just enough proteid to supply the tissue wastes 

 and of ample carbohydrate and hydrocarbon materials, the nu- 

 tritive process is impaired. It seems necessary to perfect health 

 that the supply of nitrogenous food be sufficient to allow for 

 the oxidation of some of it as circulating proteid in a manner 

 analogous to oxidation of the non-nitrogenized materials. Life 

 can be maintained on nitrogenous food alone, but it is obvious 

 that when this is done the amount of circulating proteid must 

 be enormously increased so that it may be oxidized to furnish 

 energy for the body; for those substances, the oxidation of 

 which corresponds to oxidation of the circulating proteids and 

 which furnish the main supply of energy for doing work (viz., 

 the carbohydrates and hydrocarbons), are now withdrawn from 

 the economy. It follows, conversely, that the ingestion of car- 

 bohydrates and hydrocarbons lessens the amount of proteid 

 necessary to nutrition. 



The albuminoids, such as gelatin (not meant to be included 

 under the term . " nitrogenous" foods, though they contain nitro- 

 gen), cannot take the place of tissue proteid; they may be burnt 

 in lieu of the circulating proteids and supply energy just as the 

 carbohydrates and fats do. 



It is to be remembered that any excess of proteid or albumin- 

 oid food is not discharged as such in the excreta, but undergoes 

 oxidation, the end products of which are always the same, water, 

 carbon dioxide and urea, or related substances; the develop- 



