CH. XXXIX.] SALTS OP URINE 595 



animal body, and experimental investigation shows that it is accom- 

 plished by the living cells of the kidney itself; for if a mixture of 

 glycine, benzole acid, and blood is injected through the kidney (or 

 mixed with a minced kidney just 

 removed from the body of an animal), 

 their place is found to have been taken 

 by hippuric acid. In the conversion 

 of benzoic into hippuric acid which 

 occurs in herbivora, the necessary 

 glycine comes from the kidney itself. 



The Inorganic Constituents of 

 Urine. 



The inorganic or mineral constitu- 

 ents of urine are chiefly chlorides, 

 phosphates, sulphates, and carbonates; FIG. sss. crystals of hippuric acid. 

 the metals with which these are in 



combination are sodium, potassium, ammonium, calcium, and mag- 

 nesium. The total amount of these salts varies from 19 to 25 

 grammes daily. The most abundant is sodium chloride, which 

 averages in amount 10 to 16 grammes per diem. These substances 

 are derived from two sources first from the food, and secondly as 

 the result of metabolic processes. The chlorides and most of the 

 phosphates come from the food ; the sulphates and some of the phos- 

 phates, as a result of metabolism. 



Chlorides. The chief chloride is that of sodium. The ingestion 

 of sodium chloride is followed by its appearance in the urine, 

 some on the same day, some on the next day. Some is decom- 

 posed to form the hydrochloric acid of the gastric juice. The salt 

 in the body fulfils the useful office of stimulating metabolism and 

 secretion. 



Sulphates. The sulphates in the urine are principally those of 

 potassium and sodium. Only the smallest trace enters the body with 

 the food. Sulphates have an unpleasant bitter taste (for instance, 

 Epsom salts) : hence we do not take food that contains them. The 

 sulphates vary in amount from 1*5 to 3 grammes daily. 



They are derived from the metabolism of proteins, and the 

 excretion of sulphates, though it occurs earlier than that of urea, 

 runs parallel with it. The sulphates are, therefore, like urea, the 

 result of exogenous protein metabolism. The sulphur of the protein, 

 which is endogenously katabolised, is not converted into ordinary 

 sulphates to any great extent, but reappears in the urine partly as 

 ethereal sulphates, and partly as certain obscure but not fully oxidised 

 sulphur compounds, and is usually spoken of as neutral sulphur. 



