CHAP, in.] ELIMINATION OF WASTE PRODUCTS. 651 



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 magnesium 

 in the form of chlorides, phosphates and sulphates. The exact way 

 in which the several bases and acids are combined 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 calcium chloride. 



Ammonia occurs in small quantity, alkaline carbonates are 

 frequently found, traces of nitrates are at all events occasionally 

 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 peculiarly 

 associated with the proteids, and partly from the phosphorus of 

 certain complex fats such as lecithin. When urine becomes alka- 

 line (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 insoluble, are precipitated, the sodium 

 phosphate remaining in solution. 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 sul- 

 phates 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 quantity, 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. 



403. Non-nitrogenous Bodies. These exist in very small 

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

 rence. 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 invariably 

 present in even healthy urine ; this however has not as yet been 

 placed beyond all doubt. The nature of the substances which 

 give to urine its characteristic odour has not been made out; 

 probably there are more such bodies than one. 



404. Pigments. Urine is always coloured, the tint varying 

 from a light to a dark yellow with an admixture of brown. In 

 the course of twenty-four hours, a not inconsiderable quantity of 

 pigment must leave the body by the urine ; but the nature of the 



