URIC ACID, ETC. 403 



Uric acid is readily converted into urea by oxidation, and is 

 probably one of the steps in the formation of urea which com- 

 monly occurs in the body during the gradual oxidation of the 

 proteid bodies. 



The presence of uric acid may be recognized by the murexide 

 test. The substance to be tested is gently heated in a flat cap- 

 sule with some nitric acid. A decomposition occurs, N and CO 2 

 going off, urea and alloxan remaining as a layer of yellow fluid. 

 If this be cautiously evaporated, and a drop of ammonia added, 

 a striking purple-red color is produced, which the addition of 

 potash turns violet. 



The amount of uric acid normally follows pretty closely the 

 variations in urea, but is usually only about 8 grains (.5 gramme) 

 per diem. In certain diseases the quantity may be much in- 

 creased. For the quantitative estimation, which is seldom de- 

 cided by the practitioner, the student must consult the text-books 

 of physiological chemistry. 



Kreatinin (C 4 H 7 N 3 O) is always present in urine, probably 

 being formed from kreatin by the loss of one molecule of water. 

 About 15 grains (1 gramme) is excreted per diem. 



Xanthin (C 5 H 4 N 4 Oj) also occurs in urine, but in extremely 

 small quantities. 



Hippuric acid (C 9 H 9 NO 3 ) is a normal constituent of human 

 urine, occurring, however, in very small quantities. On the other 

 hand, it is one of the most important nitrogenous constituents of 

 the urine of the herbivora, where it takes the place of uric acid. 

 Its presence depends on the existence of certain ingredients (ben- 

 zoic acid, etc.) in the food, which are capable of combining with 

 glycin, and forming a conjugated acid, a molecule of water being 

 formed at the same time, thus : 



Benzole acid. Glycin. Hippuric Acid. Water. 



C 7 H 6 2 -f C 2 H 5 N0 2 = C 9 H 9 NO + H 2 O. 

 The amount of hippuric acid increases with increased con- 

 sumption of vegetable food, in the cellulose of which the mate- 

 rials exist that are required for its formation. It is in the liver 

 that the union between the glycin and the benzoic acid takes 

 place, as is proved by the removal of that organ, when benzoic 



