38 NUTRITION OF FARM ANIMALS 



Asparagin and glutamin are respectively the amids of aspartic and 

 glutamic acids, both of which are constituents of the protein molecule. 



COOH COOH COOH COOH 



I I I I 

 CH 2 CH 2 CH 2 CH 2 



It has thus come about that the term amids has been more 

 or less commonly used as a general designation for the non-pro- 

 tein nitrogenous substances found in feeding stuffs. The usage, 

 however, is unfortunate. The word amid denotes a distinct 

 class of chemical substances of which only asparagin and glu- 

 tamin appear to be especially common in plants, while the 

 latter contain a variety of nitrogenous substances which are 

 not amids at all. The general term non-protein proposed above, 

 therefore, seems preferable. 



In addition to asparagin and glutamin there have been found 

 in feeding stuffs a large number of the cleavage products of the 

 proteins. E. Schulze 1>2)3 enumerates ten amino acids, viz., valin, 

 leucin, isoleucin, phenylalanin, tyrosin, prolin, tryptophan, 

 arginin, lysin and histidin, besides the purin bases xanthin, hy- 

 poxanthin, adenin and guanin, as well as guanidin, allantoin 

 and carnin, as having been isolated from various vegetable ma- 

 terials. Hart and Bentley 4 found that from 50 to 70 per cent 

 of the water-soluble nitrogen of a variety of feeding stuffs ex- 

 isted as amino acids or peptids, while the amid nitrogen proper 

 amounted to only 10 to 20 per cent. 



Occurrence. These substances evidently stand in a close 

 relation to the protein metabolism of the plant. They appear 

 to be in part intermediate products in the synthesis of protein 

 from nitrates and ammonium salts and in part to be formed in 

 the cleavage of proteins necessary for their translocation and 

 resynthesis during the processes of growth. They are especially 



1 Jour. f. Landw., 52 (1904), 305. 2 Ztschr. Physiol. Chem., 45 (1905), 38. 



3 Ztschr. Physiol. Chem., 47 (1906), 507. 4 Jour. Biol. Chem., 22 (1915), 477- 



