204 ORGANIC AGRICULTURAL CHEMISTRY 



into body protein. It seems probable that part of the protein 

 is oxidized immediately and never forms body protein. This 

 may take place with the entire blood protein molecule, or it is 

 possible that in being synthesized into the various forms of 

 body protein certain groups of the blood protein are unadapted 

 for the synthesis of the body protein and these portions then 

 become oxidized. 



While we cannot therefore follow with any definiteness the 

 conversion of food protein into body protein or state definitely 

 whether katabolized protein is body protein or blood protein 

 (food protein), we can follow in certain detail the results of the 

 katabolism of protein in the body. 



Katabolism of Proteins. — We have thus far discussed, 

 though without a much to be desired definiteness in detail, the 

 conversion of food protein into body protein. It remains to 

 consider the reactions and results of the katabolism or degrada- 

 tion of protein and the oxidation by which it, like carbohydrates 

 and fat, yields energy to the animal body. For a long time it 

 was held that protein alone was the material of the body from 

 which muscular energy was derived. This is not now considered 

 as true, for it has been shown that both carbohydrates and fats 

 contribute to the supply of muscular energy. 



Katabolic Products. — In considering the katabolic or tear- 

 ing down changes of protein it is necessary to remember that 

 proteins, because of their containing nitrogen as well as carbon, 

 hydrogen and oxygen, may be looked upon as consisting of two 

 parts, viz. (i) a carbon, hydrogen and oxygen part, which acts 

 like the carbohydrates and fats and on oxidation yields carbon 

 dioxide and water as the products, (2) a nitrogen-containing 

 part, also containing carbon, hydrogen and oxygen, which on 

 oxidation yields distinctly different products. It is not meant 

 that in the protein molecule there are two separate portions united 

 together, but simply that by their oxidation two classes of prod- 

 ucts are formed. It is through a study of these end products of 

 protein katabolism that we gain an insight into the process itself. 



When protein is oxidized in an excess of oxygen, as in a calo- 



