518 COMPOSITION OF URINE [BOOK n. 



proteid and other complex bodies. In the ash of urine there is 

 rather more sulphur than corresponds to the sulphuric acid 

 directly determined ; this indicates the existence in urine of 

 some sulphur-holding complex body. And there are traces of 

 iron, pointing to some similar iron-holding substance. But 

 otherwise, all the substances found in the ash exist as salts in 

 the natural fluid. 



The chief bases are sodium, potassium, calcium and mag- 

 nesium in the form of chlorides, phosphates and sulphates. 

 The exact way in which the several bases and acids are com- 

 bined is to some extent a matter of uncertainty ; but sodium 

 chloride is certainly present and in considerable quantity ; it is 

 the most abundant and important inorganic constituent. A 

 large portion of the phosphoric acid seems to exist as acid 

 sodium phosphate, the rest as soluble calcium and magnesium 

 phosphates. The remaining chief salts, occurring however in 

 smaller quantity, are potassium and sodium sulphate, and cal- 

 cium chloride. 



Ammonia occurs in small quantity, alkaline carbonates are 

 frequently found, traces of nitrates are at all events occa- 

 sionally present, as also indications of silicates and of sulpho- 

 cyanates. 



The phosphates are derived partly from the phosphates 

 taken as such in food, partly from the phosphorus or phosphates 

 pecaliarly associated with the proteids, and partly from the 

 phosphorus of certain complex fats such as lecithin. When 

 urine becomes alkaline (and, as we shall presently see, it may 

 do so by changes taking place in itself) the calcic and magnesic 

 phosphates are converted into basic salts which, being insolu- 

 ble, are precipitated, the sodium phosphate remaining in solu- 

 tion. When the alkalinity, as is frequently the case, is due to 

 ammonia, ammonio-magnesium phosphate is formed and is apt 

 to appear in crystals. The sulphates are derived partly from 

 the sulphates taken as such in food and partly from the sulphur 

 of the proteids. The carbonates, when occurring in large quan- 

 tity, generally have their origin in the oxidation of such salts 

 as citrates, tartrates, &c. The bases present depend largely on 

 the nature of the food taken. Thus with a vegetable diet, the 

 excess of the alkalis in the food reappears in the urine ; with 

 an animal diet, the earthy bases in a similar way come to the 

 front. 



323. Norirnitrogenous Bodies. These exist in very small 

 quantities, and many of them are probably of uncertain oc- 

 currence. Some of these are organic acids, the most constant 

 perhaps being oxalic acid ; to this may be added glycerin- 

 phosphoric, lactic, formic, acetic, butyric and possibly succinic 

 acids. Inosit has also been said to occur normally. It has 

 been maintained that minute quantities of sugar (dextrose) are 



