362 THE URINE. 



especially extensive disease or extirpation of the kidneys, the 

 separation of urine is imperfect, the urea is found largely in 

 the blood and in most other fluids of the body. 



Uric Add. This, which is another nitrogenous animal sub- 

 stance, with the formula C 5 N 4 

 FlG - 127 - H 4 O 3 , and was formerly termed 



lithic acid, on account of its 

 existence in many forms of 

 urinary calculi, is rarely ab- 

 sent from the urine of man or 

 animals, though in the feline 

 tribe it seems to be sometimes 

 entirely replaced by urea (G. 

 Bird). Its proportionate quan- 

 tity varies considerably in dif- 

 ferent animals. In man, and 

 Mammalia generally, especially 

 the Herbivora, it is compara- 

 tively small. In the whole 



Various forms of uric acid crystals. , .1 /? > -i i ( 



tribe oi birds and 01 serpents. 



on the other hand, the quantity is very large, greatly exceed- 

 ing that of the urea. In the urine of granivorous birds, in- 

 deed, urea is rarely if ever found, its place being entirely sup- 

 plied by uric acid. The quantity of uric acid, like that of 

 urea, in human urine, is increased by the use of animal food, 

 and decreased by the use of food free from nitrogen, or by an 

 exclusively vegetable diet. In most febrile diseases, and in 

 plethora, it is formed in unnaturally large quantities ; and in 

 gout it is deposited in, and in the tissues around, joints, in the 

 form of urate of soda, of which the so-called chalkstones of 

 this disease are principally composed. 



The condition in which uric acid exists in solution in the 

 urine has formed the subject of some discussion, because of its 

 difficult solubility in water. 



According to Liebig the uric acid exists as urate of soda, 

 produced, he supposes, by the uric acid, as soon as it is formed, 

 combining with part of the base of the alkaline phosphate of 

 soda of the blood. Hippuric acid, which exists in human 

 urine also, he believes, acts upon the alkaline phosphate in 

 the same way, and increases still more the quantity of acid 

 phosphate, on the presence of which it is probable that a part 

 of the natural acidity of the urine depends. It is scarcely 

 possible to say whether the union of uric acid with the base 

 soda and probably ammonia, takes place in the blood, or in 

 the act of secretion in the kidney ; the latter is the more 

 probable opinion ; but the quantity of either uric acid or 



