378 THE UEINE. 



specific gravity. If a smaller quantity of water than usual be taken 

 into the system with the drink, or if the exhalation from the lungs and 

 skin, or the intestinal discharges, be increased, a smaller quantity of 

 water will necessarily pass off by the kidneys ; and the urine will be 

 diminished in quantity, while its specific gravity is increased. The 

 urine is sometimes reduced in this way to 500 or 600 cubic centimetres 

 per day, its specific gravity rising at the same time to 1030. On the 

 other hand, if the fluid ingesta be unusually abundant, or if the per- 

 spiration be diminished, the surplus quantity of water will pass off by 

 the kidneys ; so that the amount of urine in twenty- four hours may be 

 increased to 1350 or 1400 cubic centimetres, and its mean specific 

 gravity reduced at the same time to 1020 or even 1017. Under such 

 conditions, the total amount of solid matter discharged remains about 

 the same. These changes depend simply upon the fluctuating quantity 

 of water, which may pass off by the kidneys in larger or smaller quan- 

 tity, according to circumstances. In purely normal or physiological 

 variations of this nature, the entire quantity of the urine and its mean 

 specific gravity vary always in an inverse direction with regard to each 

 other ; the former increasing while the latter diminishes, and vice versa. 

 If, however, it be found that both the quantity and specific gravity of 

 the urine are increased or diminished at the same time, or if either one 

 be increased or diminished while the other remains stationary, such an 

 alteration will show an actual change in the total amount of solid ingre- 

 dients, and consequently an unnatural and pathological condition. 



Ingredients of the Urine. 



The chemical composition of the urine, as derived from the most 

 recent and numerous analyses, is as follows: 



Nitrogenous 



organic 

 substances. 



Mineral salts. 



COMPOSITION OF THE UKINE. 



Water 950.00 



Urea 26.20 



Creatinine 0.87 



Sodium and potassium urates . . . 1.45 



Sodium and potassium hippurates . . 0.70 



Sodium biphosphate ..... 0.40 



Sodium and potassium phosphates . . 3.35 



Lime and magnesium phosphates . . 0.83 



Sodium and potassium chlorides . . 12.55 



Sodium and potassium sulphates . . 3.30 



Mucus and coloring matter . . . 0.35 



1000.00 



The constitution of the urine is not invariable, but changes more or 

 less at different periods of the day, according to the rapidity of excre- 

 tion of its different ingredients. The foregoing list, however, repre- 

 sents, in an approximate manner, its average composition for the entire 

 twenty-four hours. 



