56 THE CHEMISTRY OF CATTLE FEEDING 



Occurrence. Some of the amino compounds mentioned in 

 the tables, e.g. betaine, asparagine, glutamine, are probably 

 not formed by animals ; others, e.g. urea, uric acid, guanine, 

 are not known to occur in plants. Leucine, tyrosine, and some 

 others are commonly found in the juices of both kinds of 

 organism. They are known to be amongst the most impor- 

 tant products of the putrefactive decay of proteins, and they 

 are probably also formed as intermediate products in the 

 process of digestion of these compounds by animals. 



Sarcosine occurs in the juice of flesh. Betaine is produced 



QTT 



by the oxidation of choline, QH^/r \ It has 



been found in cotton seeds, malt, and malt coombs. It occurs 

 in larger quantities in sugar beet, and may be recovered from 

 the molasses. 



Leucine is produced by pancreatic digestion of fibrine and 

 other proteins. It occurs normally in the spleen and lymph- 

 glands. Isomeric forms are present in many plants, and may 

 be obtained from conglutin the globulin of lupines. 



Asparagine was so called because it was first obtained from 

 asparagus. It occurs also in beetroot, peas, beans, vetches, 

 and, generally, in all sprouting and young vegetable tissues. 

 The asparagine and aspartic acid found in sprouting seeds is 

 probably derived from the protein compounds which are thus 

 transferred to the growing points and re-elaborated. It has 

 been asserted that the proteins of plants are mainly formed by 

 condensation of asparagine aldehyde. It is tolerably certain, 

 however, that other amino compounds, e.g. tyrosine, trypto- 

 phane, etc., which contain benzene rings take part in these 

 reactions. Cystin or other sulphur containing molecules are 

 also necessary to complete the process. 



Urea or carbamide, the amide of carbonic acid, CO(OH) 2 , 

 was originally discovered in urine of which it is the chief 

 nitrogenous constituent. This means that the metabolic 

 products resulting from the oxidation of the nitrogenous tissues 

 are excreted chiefly in the form of urea. An adult man 

 excretes about 30 grams of urea, over i oz. per day. Urea was 

 subsequently prepared from ammonium isocyanate a reaction 



