THE URINARY SYSTEM. 387 



deposits may also occur in urine, and are usually indicative of abnormal 

 processes taking place either in the body or in the urine itself. The 

 nature of the deposits varies with the reaction of the urine. 



In acid urine those most frequently seen are, first, uric acid crystals, 

 which assume the form of whetstones or cylinders, and are usually, 

 though not invariably, pigmented ; and, secondly, calcium oxalate, 

 occurring as small colourless octohedra, often called " envelope " 

 crystals from their appearance under the microscope. 



Uric acid and oxalate crystals are frequently found together. Other 

 crystalline deposits, occasionally met with in acid urine, are cystine 

 (flat hexagonal colourless plates) and the acid urates of sodium or 

 ammonium, which form spheroidal masses with projecting spikes. 



In alkaline urine, the crystals most commonly met with are (1) 

 earthy phosphates, star-shaped in appearance, and (2) ammonio- 

 magnesium phosphate, NH 4 MgP0 4 . The latter, often called " triple 

 phosphate," is formed when urine becomes alkaline as a result of 

 the bacterial decomposition of urea ; the crystals are large and very 

 characteristic, resembling knife-rests or coffin lids. 



OTHER ABNORMAL CONSTITUENTS IN URINE. 



(1) Coagulable Protein. Except for a trace of nucleo-protein, 

 normal urine contains no protein. In disease of the kidney, serum 

 globulin and albumin escape from the blood into the urine, and are 

 coagulated on boiling the urine (after the addition of a drop or two of 

 dilute acetic acid). Further, when urine containing protein is poured 

 on to the surface of strong nitric acid, a precipitate forms at the junc- 

 tion of the two fluids (Heller's test). 



(2) Sugar. The conditions under which sugar occurs in urine have 

 already been dealt with (p. 350). In man the usual cause of glyco- 

 suria is diabetes, and the sugar is dextrose Lactose is sometimes 

 found during lactation, even in healthy women. In rare cases the 

 urine contains Isevulose or pentose. The amount of dextrose present 

 in the urine in diabetes may vary from mere traces up to 350 to 500 

 grams daily. 



Dextrose reduces alkaline solutions of copper sulphate, yielding 

 cuprous oxide. The solutions generally used in testing for dextrose 

 are (1) Fehling's solution, containing copper sulphate, caustic potash, 

 and Rochelle salt, which keeps the cupric hydrate in solution, or (2) 

 Benedict's solution, which contains copper sulphate, sodium carbonate, 

 and sodium citrate. The latter is more satisfactory, since, unlike 

 Fehling's solution, it is not reduced at all by uric "acid or creatinine, 



