182 PLANT PRODUCTS 



is the relative proportion of important ring compounds, 

 like indole, benzene, or purine. The reason why the so- 

 called amides have little value is that the compounds 

 which yield ammonia on hydrolysis are plentiful in the 

 products of hydrolysis of the protein in most cattle foods. 

 Compounds like aspartic and glutaminic acids will probably 

 supply twenty times as much nitrogen as substances of 

 the tryptophane type, hence the indole groupings are 

 comparatively scarce, and, therefore, valuable, whilst the 

 simple amino acids, like aspartic acid, are plentiful, and, 

 therefore, not very valuable. All these substances are 

 probably utilized by the animal, but those that are scarce 

 in amount are the ones whose supply we have to consider. 

 Under special conditions even ammonium acetate has proved 

 useful for increasing the protein laid on by beasts. Never- 

 theless, no very practical system has yet been discovered 

 to obtain a clear idea of the value of the different proteins 

 in the foods. 



The metabolic changes of the fats result in hydrolysis, 

 oxidation, and production of sugars. The sugars themselves 

 break down with the production of carbonic acid. The 

 proteins are chiefly concerned in the building up and repairing 

 of the structural part of the animal body, the fats and the 

 sugars being chiefly concerned with the production of 

 energy. 



REFERENCES TO SECTION I 



Wood and Yule, " Statistics of British Feeding Trials, and the Starch 



Equivalent Theory," Journ. Agric. Science, vi., p. 233. 



Wood and Hill, " Skin Temperature and Fattening Capacity in Oxen," 



Journ. Agric. Science, vi., p. 252. 



Hall, " Agriculture after the War," p. 39. (Murray.) 



Armsby, " The Principles of Animal Nutrition." 



Bennett, " Animal Proteids." (Bailliere, Tindall and Cox.) 



Luck, " The Elements of the Science of Nutrition." (Philadelphia.) 



