FOODS IN NUTRITION 1 73 



piece of iron rusts completely away in five years as when it is con- 

 sumed in an atmosphere of oxygen in five minutes. In both 

 cases it is oxidized In the cell oxidation is continually going 

 on with the production of heat and of certain excrementitious 

 (oxidation) products depending on the kind of food-stuffs. 



Fate of Different Foods in the Organism. In the first 

 place, the foods may be divided, into (I) those which pass through 

 the organism unchanged and (II) those which lose their identity 

 and are discharged as bodies different from those which entered. 

 The first class includes the foods furnishing no energy; the second 

 those furnishing energy. 



Only a few foods undergo in the body reactions which alter 

 their identity. They may be regarded as already digested and, in 

 fact, when dissolved, ready for discharge from the body. They 

 are, however, useful and necessary constituents of the body, and 

 if they do not take a considerable active part in nutrition, their 

 favorable influence on that process makes them essential to 

 health. The foods producing no energy may be dismissed with 

 a repetition of the statement that they are largely introduced in 

 connection with the proteid foods from which they cannot be 

 separated without destruction of the proteid molecule. Indeed, 

 all the proteid food introduced, whether animal or vegetable, 

 contains inert constituents as a part of the molecule, and these 

 seem as necessary to nutrition as do the energy furnishing con- 

 stituents. The foods furnishing energy and those furnishing no 

 energy enter, are deposited, and seem to be discharged both 

 together. The few reactions which the inert foods undergo in 

 the body do not materially affect the supply of energy. 



(II) The proteids, carbohydrates and hydrocarbons are all con- 

 sumed in the organism, none (unless they have accidentally 

 escaped digestion) being discharged as they entered. 



i. The nitrogenous foods are changed into peptones in the 

 alimentary canal, undergo some unknown change in their ab- 

 sorption therefrom, appear in the blood as the proteid constitu- 



