456 THE URIXE. 



the body, e.g., the humours of the eye (Millon), even while 

 the functions of the kindeys are unimpaired : but when 

 from any cause, 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 Acid. This, which is another nitrogenous animal 

 p- I27 * substance, with the for- 



mula C 5 N 4 H 4 O 3 , and was 

 formerly termed lithic acid, 

 on account of its existence 

 in many forms of urinary 

 calculi, is rarely absent 

 from the urine of man or 

 animals, though in the 

 feline tribe it seems to 

 be sometimes entirely re- 

 placed by urea (G. Bird). 

 Its proportionate quantity 

 varies considerably in different animals. In man, and 

 Mammalia generally, especially the Herbivora, it is com- 

 paratively small. In the whole tribe of birds and of 

 serpents, on the other hand, the quantity is very large, 

 greatly exceeding that of the urea. In the urine of grani- 

 vorous birds, indeed, urea is rarely if ever found, its place 

 being entirely supplied 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 chalk-stones of this disease 

 are principally composed. 



* Fig. 127. Various forms of uric acid crystals. 



