URINE 115 



in which he passed strong alternating currents through solutions of 

 proteid-like materials. Such alternating currents are certainly 

 absent in the body, but their effect, which is a rapidly changing series 

 of small oxidations and reductions, is analogous to metabolic pro- 

 cesses ; under such circumstances the carbon atoms are burnt off as 

 carbon dioxide, the nitrogen being split off in the form of ammonia, 

 and by the union of these two substances ammonium carbonate is 

 formed. 



The following structural formulae show the relationship between 

 ammonium carbonate, ammonium carbamate, and urea. 



^=^<0.NH4 ^-^<0.NH4 ^-^NHa 



[ammoniam carbonate] [ammoniam carbHmate] [urea or carbamide] 



The loss of one molecule of water from ammonium carbonate pro- 

 duces ammonium carbamate ; the loss of a second molecule of water 

 produces urea. 



THE INORGANIC CONSTITUENTS OF URINE 



The inorganic or mineral constituents of urine are chiefly chlorides, 

 phosphates, sulphates, and carbonates ; the metals with which these 

 are in combination are sodium, potassium, ammonium, calcium, and 

 magnesium. 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 13 grammes per diem. These substances 

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

 result of metabohc processes. The chlorides and most of the phos- 

 phates come from the food ; the sulphates and some of the phosphates 

 are a result of metabolism. The salts of the blood and of the urine 

 are much the same, with the important exception that, whereas the 

 blood contains only traces of sulphates, the urine contains abundance 

 of these salts. The sulphates are derived from the changes that occur 

 in the proteids of the body ; the nitrogen of proteids leaves the body 

 as ure^ and uric acid ; the sulphur of the proteids is oxidised to form 

 sulphuric acid, which passes into the urine in the form of sulphates. 

 The execretion of sulphates, moreover, runs parallel to that of urea. 

 The chief tests for the various salts have been given in the practical 

 exercises at the head of this lesson. 



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 decomposed to form the 

 hydrochloric acid of the gastric juice. The salt, in passing through 



i2 



