DISEASES OF THE URINARY SYSTEM. 259 



Uric acid is insoluble in alcohol and ether, and very 

 feebly soluble in water. 



Hippuric Acid. — Hippuric acid (C^H^^NOg) occurs in 

 very small proportion in the urine of man (less than "1 per 

 cent.) and carnivora, but is present in abundance as 

 alkaline hippurates in that of herbivorous animals. Hippuric 

 acid is a beautiful white crystalline substance, soluble in 

 400 parts of cold water. It is also soluble in ether and 

 alcohol. 



When the quantity of urea in the urine is small, that of 

 hippuric acid is large, and vice versa. It varies from five 

 to fifteen parts in 1,000 of the urine of the horse (Bibra). 



Hippuric acid crystallizes in long, transparent, four-sided 

 prisms, and may be readily obtained by boiling the urine of 

 an herbivore and adding hydrochloric acid. 



It is noteworthy that in all animals in which the urine 

 contains much hippuric acid, as in the horse, indigo is also 

 present in relatively large quantities (Sanderson). 



Hippuric acid is said to be formed in the system from the 

 benzoic acid, or bodies which yield benzoic acid, which is 

 ingested. 



This acid is also said to appear in the urine of man and 

 herbivora whenever benzoic acid (C-HgOo) enters the 

 system, glycin (glycocoll) being taken up and water given 

 off-. 



Extractives. — The extractives found in the urine of the 

 horse are creatin, creatinin, lactic acid, benzoic acid, and 

 several others. 



Pigmentary Matter. — The pigmentary or colouring 

 matters of the urine of the horse are not of much physio- 

 logical importance. 



Inorganic Salts. — The urine of carnivora contains 

 sulphates, chlorides, and phosphates ; that of herbivora 

 contains a large percentage of carbonates, with some 



.17—2 



