332 



FUNCTIONS OP NUTRITION. 



fying its color. 



FIG. 80. 



They, however, decompose its urates ; and the uric acid 

 thus set free is slowly deposited 

 in the crystalline form. If ni- 

 tric or hydrochloric acid be added 

 to fresh filtered urine, in the pro- 

 portion of about 2 per cent, by 

 volume, and the mixture al- 

 lowed to remain at rest for 

 twenty-four hours, the sides and 

 bottom of the vessel become cov- 

 ered with a thin deposit of uric 

 acid crystals. These crystals 

 are usually transparent rhom- 

 boidal plates, with their obtuse 

 angles rounded off, and tinged 

 of a yellowish hue by the col- 

 oring matter of the urine. They 



CRYSTALS OF URIC ACID; deposited from urine, after are frequently arranged in radl- 

 the addition of nitric acid. , 



ated clusters, or small spheroi- 

 dal masses, which vary in size and regularity, according to the time 

 occupied in their formation. 



When the urine is scanty and concentrated, with a specific gravity of 

 1030 or 1035, but without abnormal ingredients, if mixed with half its 

 volume of nitric acid and exposed to a low temperature, it will soon 

 become filled with an abundant crystallization of nitrate of urea. In 

 urine of this specific gravity, the water is still sufficient to hold the urea 

 in solution, but allows a separation of nitrate of urea on the addition of 

 nitric acid. This never takes place in urine of normal specific gravity. 



Alkalies. The addition of an alkali or alkaline carbonate to normal 

 urine diminishes its acid reaction, and, when the point of saturation is 

 reached, produces a turbidity, owing to precipitation of the earthy phos- 

 phates. These are the only ingredients of the urine liable to be thrown 

 down by an alkali. 



Mineral Salts. Solutions of barium chloride, barium nitrate, or tri- 

 basic lead acetate, added to healthy urine, decompose its sulphates, pro- 

 ducing a dense precipitate of the corresponding metallic salts. Solu- 

 tions of silver nitrate produce a precipitate with the sodium and 

 potassium chlorides, forming the insoluble silver chloride. Tribasic 

 lead acetate and silver nitrate also throw down mucus and coloring 

 matters. 



Abnormal Ingredients of the Urine, 



The abnormal ingredients which appear in the urine are either : 1st. 

 Foreign substances accidentally present in the blood and eliminated by 

 the kidneys, such as glucose, biliary matters, medicinal and poisonous 

 substances; or 2d. The albuminous constituents of the blood, discharged 

 with the urine owing to disturbance of the renal circulation. 



Glucose. The presence of glucose in the urine is characteristic of 



