THE CHEMISTRY OF THE ANIMAL BODY 168 



itc, and the mineral matter are chiefly excreted from the 

 blood, by the kidneys and appear in the urine. 



Urine. — Urine vaiies greatly in composition, being affected 

 by the food, amount of exercise, water consumed and other 

 circumstances. In carnivorous animals it is usually acid, in 

 herbivora alkaline or neutral. The characteristic constituent 

 is urea^ or carhamlde, C0(NH2)a, of which there is usually more 

 in the urine of carnivora than in that of herbivora. 



Uric acid, H2C6H2N4O3, occurs very largely in the excre- 

 ments of birds and reptiles, also in the urine of carnivora, and 

 to a small extent in that of herbivora. In certain diseases — 

 e.g., gout and rheumatism — deposits of mic acid aiid urates 

 are formed in the body. 



In the mine of herbivorous animals, uiic acid is replaced 

 by hijypuric acid (benzoyl-amino- acetic acid), C9H9NO3, which 

 occurs to the "extent of about 2 per cent, in the mine of horses 

 and catt'e. By hydrolysis (taking up of water) hippuric acid 

 readily p isses into benzoic acid, CeHs.COOH, and amino- 

 acetic acid, or glycocoU, CH2(NH2).COOH : 



C6H5CO.NH.CH2.COOH + H2O 

 =C«H6.C00H +CH2(NH2).COOH. 



