386 THE URINE. 



tals of uric acid. This deposit may be distinguished from albumen by 

 the appearance of the crystals under the microscope, and also by the 

 fact that, unlike albumen, it is not produced by the application of a 

 boiling temperature. 



When the urine is scanty and concentrated, owing to temporary causes, 

 with a specific gravity of 1030 to 1035, but without any abnormal in- 

 gredient, if it be mixed with one-half its volume of nitric acid and 

 exposed to a low temperature, a crystallization of nitrate of urea will 

 often take place in the course of half an hour or an hour. This is 

 clue simply to the diminished proportion of water, which is still suffi- 

 cient to hold 'the urea in solution, but allows a separation of nitrate of 

 urea when this salt is formed by the addition of nitric acid. It never 

 takes place when the urine has its normal specific gravity of 1020 to 

 1025. 



Alkalies. The addition of a free alkali or an alkaline carbonate to 

 normal urine diminishes its acid reaction, and, as soon as the point of 

 saturation has been reached, produces a turbidity, owing to the pre- 

 cipitation of the earthy phosphates. These are the only ingredients of 

 the urine which are thrown down by the addition of an alkali, and a 

 free acid immediately restores its transparency. 



Mineral Salts. Solutions of barium chloride, barium nitrate, or the 

 tribasic lead acetate, when added to healthy urine, decompose its sul- 

 phates, and produce a dense precipitate of the corresponding metallic 

 salts. Solutions of silver nitrate produce a precipitate with the sodium 

 and potassium chlorides, forming silver chloride which is insoluble. The 

 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, which are elimi- 

 nated by the kidneys, such as glucose, biliary matters, and medicinal 

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

 discharged with the urine owing to a disturbance of the renal circulation. 



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

 diabetes mellitus. In this disease the urine is generally increased in 

 quantity and at the same time of unusually high specific gravity, namely, 

 from 1035 to 1050. It is of a light, clear, amber or straw color, and 

 remarkably transparent ; so that it has the appearance of being dilute, 

 although it is in reality denser than usual, owing to the presence of 

 glucose in solution. The glucose is detected by the application of Trom- 

 mer's or Fehling's test, or by that of fermentation. For the latter pur- 

 pose a little yeast should be mixed with 15 or 20 times its volume of 

 water, and the mixture allowed to remain at rest in a cylindrical upright 

 glass vessel until the yeast globules have subsided in a dense homo- 

 geneous layer at the bottom. The supernatant fluid, containing the 





