218 THE FLUIDS. 



in practice, since the specific gravity averages not more than 1020, 

 and is generally rather less than this, according to most writers. 



Of all the constituents in solution in the urine, urea is the most 

 important. Its proportional as well as its absolute amount varies 

 extremely, the kind of food having a great influence in this respect 

 (p. 69). An increased secretion of water is also accompanied by 

 &n increased amount of urea, in the twenty-four hours. E. g. if 

 1,000 grains of urine be secreted in twenty-four hours, 33 grains 

 are urea; if 2,000 grains, about 42 grains of urea; and if 3,000 

 grains of urine, about 50 of urea. Of course the specific gravity 

 will be lowest in the last case, so that the amount of urea in one 

 thousand parts of urine will be least of all. It has been seen that 

 the urea is derived directly from the nitrogenized elements of the 

 food and of the decomposed tissues (p. 69). 



Of uric acid, from 7.7 to 13.9 grains are excreted in the urine, 

 by an adult, in twenty-four hours. Its amount depends less on the 

 kind of food taken than on the internal conditions of the organism 



(P- 64). 



Creatine and creatinine (pp. 67, 68) are normal constituents of the 

 urine, but their amount has not been determined. 



Formic acid is sometimes found in healthy urine, in very small 

 quantities. Hippuric acid is hardly more abundant than the uric. 



Lactic acid is not found in normal urine, but at once occurs in 

 those states of the organism in which the process of oxidation is 

 interfered with (pp. 60, 66). 



The chlorides of sodium and potassium are very abundant in 

 urine. An adult secretes about 162 grains of chlorine in twenty- 

 four hours. They greatly diminish, or even entirely disappear, in 

 diseases accompanied by copious exudations as in acute dropsy, 

 acute Blight's disease, acute tuberculosis, in violent diarrhoeas, cho- 

 lera, typhus, and pneumonitis. 



The sulphates are found in variable quantities. An adult ave- 

 rages 31.4 grains of sulphuric acid in twenty-four hours. They 

 are increased only by violent bodily exercise (as in convulsions and 

 delirium tremens), and in high mental excitement. 



The acid phosphate of soda (p. 57) is the principal source of the 

 acid reaction of the urine. The phosphates of lime and magnesia 

 are also found in considerable amount, and in the proportion, on an 

 average, of 15 to 7. An adult discharges, on an average, 49.4 to 

 80.2 grains of phosphoric acid in twenty -four hours, and 15.4 grains 



