CH. XXX1X.J URINARY DEPOSITS 599 



acid. It is soluble with difficulty in hydrochloric acid. Calcium 

 oxalate calculi are the commonest kind of stones in the kidney. 



FIG. 335. Crystals of calcium oxalate. FIG. 386. Crystals of cystin. 



Deposit of Cystine. Cystine (C 6 H 12 N 2 S 2 4 ) is recognised by its 

 colourless six-sided crystals (fig. 386). These are rare: they occur 

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

 Cystinuria (cystine in the 'urine) is hereditary. 



Deposit of Phosphates. These occur in alkaline urine. The 

 urine may be alkaline when passed, due to fermentative changes 

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

 (unless the air is perfectly pure, as on the top of a snow mountain), 

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

 urece. This forms ammonium carbonate from the urea. 



CON 2 H 4 + 2H 2 .. (NH 4 ) 2 C0 3 . 



[Urea.] [Water.] [Ammonium 



carbonate.] 



The ammonia renders the urine alkaline and precipitates the 

 earthy phosphates. The chief forms of phosphates that occur in 

 urinary deposits are 



(1) Calcium phosphate, Ca 3 (P0 4 ) 2 ; amorphous. 



(2) Triple or ammonio-magnesium phosphate, MgNH 4 P0 4 ; coffin- 

 lids and feathery stars (fig. 384). 



(3) Crystalline phosphate of calcium, CaHP0 4 , in rosettes of 

 prisms, in spherules, or in dumb-bells. 



(4) Magnesium phosphate, Mg 3 (PQ 4 ) 2 + 22H 2 0, occurs occasion- 

 ally, and crystallises in long plates. 



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

 without effervescence. 



A solution of ammonium carbonate (1 in 5) eats magnesium 

 phosphate away at the edges ; it has no effect on the triple phosphate. 

 A phosphate of calcium (CaHP0 4 + 2H 2 0) may occasionally be 



