URINE 



127 



Deposit of Cystm.— Cystin (C6H,2N2S204) is recognised by its 

 colourless six-sided crystals (fig. 50). These are rare: they occur 

 only in acid urine, and they may form concretions or calculi. Cystin- 

 uria (cystin in the urine) is hereditary. 



Deposit of Phosphates. — These occur in alkaline urine. The 

 urine may be alkahne when passed, due to fermentative changes 

 occurring in the bladder. All urine, however, if exposed to the air 

 (unless the air is pei-fectly pure, as on the top of a snow mountain), 

 will in time become alkaline owing to the growth of the micrococcus 

 urea. This forms ammonium carbonate from the urea. 



CONjH, + 2H2O = (NH4)2C03 



[nrea] [water] [ammoniam 



carbonate] 



The ammonia renders the urine alkaline and precipitates the 

 earthy phosphates. The chief forms of phosphates that occur in 

 urinar}' deposits are — 



1, Calcium phosphate, Ca3(P04), ; amorphous. 



Fig. 51. — Triple phosphate erystalsw 



Fig. S3. — Crystals of phosphate of lime 

 (stellar phosphate). 



2. Triple or ammonio-magnesium phosphate, MgNH4P04 ; coflBn- 

 lids and feathery stars (fig. 51). 



3. Crystalhne phosphate of calcium, CaHPOi, in rosettes of 

 prisms, in spherules, or in dumb-bells (fig. 52). 



4. Magnesium phosphate, Mg3(P0i).>-f 22H.>0. occurs occasion- 

 ally, and crystallises in long plates. 



All these phosphates are dissolved by acids, such as acetic acid, 

 without effervescence. 



They do not dissolve on heating the urine ; in fact, the amount 

 of precipitate may be increased by heating. Ven,- often neutral or 



