THE URINE. 331 



or diminished according to its amount in various articles of diet. Its 

 discharge is usually least during the night, increases in the forenoon, 

 and is greatest during the latter part of the day. According to Yogel,* 

 both mental and bodily exertion perceptibly augment its excretion ; 

 and even water, when taken in unusual quantity, by increasing the 

 activity of the kidneys, causes a more abundant discharge of sodium 

 chloride, subsequently followed by a corresponding diminution. The 

 average amount of chlorides eliminated with the urine is about fifteen 

 grammes per day. 



Sodium and Potassium Sulphates. The sulphates in the urine are 

 derived partly from those introduced with the food. Their quantity 

 is increased by the administration of sulphuric acid or of sodium sul- 

 phate ; and the administration of sulphur or a sulphuret produces the 

 same effect. They are most abundant under a diet of animal food, 

 owing to the sulphur contained in albuminous matters, which is finally 

 eliminated in the form of sulphates. These salts are freely soluble and 

 never appear as a precipitate in the urine. Their average quantity is 

 about 3.96 grammes per day. 



Reactions of the Urine to Chemical Tests. 



The reactions of the urine to various ordinary tests form a ready cri- 

 terion for ascertaining its normal or abnormal constitution. The exact 

 quantitative determination of its ingredients requires the skill of the 

 professional chemist ; but many of its important characters may be 

 recognized by simple means. 



Application of Heat. If healthy urine, of a distinctly acid reaction, 

 be heated to the boiling point, no change in its appearance is produced ; 

 but if its acidity be very slight, it may become turbid on boiling, from 

 a precipitation of earthy phosphates. These phosphates are less soluble 

 in a hot than in a cold liquid ; and a faintly acid reaction, which may 

 hold them in solution at ordinary temperatures, becomes insufficient 

 under the application of heat, and the phosphates are precipitated. The 

 deposit from this cause is never very abundant, and is at once redis- 

 solved by the addition of any acid sufficient to restore the normal reac- 

 tion of the urine. The precipitation of the earthy phosphates by boiling 

 is, therefore, due, not to an increased quantity of these salts, but to 

 deficient acidity of the urine. 



Diseased urine may become turbid on boiling, from the coagula- 

 tion of albumen. This is distinguished from a precipitation of the 

 earthy phosphates by two facts namely, first, that it may take place 

 in urine which is distinctly acid ; and second, that the addition of nitric 

 acid, which redissolves the phosphatic precipitate, only increases the 

 turbidity due to albumen. 



Acids. The addition of mineral acids to healthy urine produces no 

 immediate visible effect, beyond increasing its acidity and slightly modi- 



* Analyse des Harns. Wiesbaden, 1872, p. 350. 



