THE COMPOSITION AND CHARACTERS OF URINE. 407 



stance. 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 uncer- 

 tainty ; but sodium chloride is certainly present and in considerable quan- 

 tity ; 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 indica- 

 tions of salicylates 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 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 insoluble, are pre- 

 cipitated, the sodium phosphate remaining in solution. When the alka- 

 linity, 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 quantity, 

 generally have their origin in the oxidation of such salts as citrates, tartrates, 

 etc. The bases present depend largely on the nature of the food taken. 

 Thus with a vegetable diet, the excess of the alkalies in the food reappears 

 in the urine ; with an animal diet, the earthy bases in a similar way come 

 to the front. 



339. Non-nitrogenous bodies. These exist in very small quantities, 

 and many of them are probably of uncertain occurrence. 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 pres- 

 ent 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 character- 

 istic odor has not been made out ; probably there are more such bodies than 

 one. 



340. Pigments. Urine is always colored, 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 normal pigment or pigments of urine 

 is at present obscure and the subject of much controversy. The matter 

 is apparently further complicated by the presence in urine of what have 

 been called " chromogens," that is to say, bodies which are not colored 

 themselves but which readily give rise to pigments upon oxidation ; and it 

 is probable that some of these " chromogens " of the urine are reduction 

 products of the respective pigments, the reduction taking place in the 

 urine after secretion, or during or even before secretion. There is frequently 

 present in urine, especially in cases of fever, a pigment which has been 

 isolated and determined, which has a characteristic spectrum, and which, 

 being maintained by some to be a derivative of bilirubin, has been called 

 urobilin. It is not this urobilin, however, which gives to urine its ordinary 



