CH. xxxvii.] URINARY DEPOSITS. 565 



Crystals of calcium oxalatc may be mixed with this deposit 

 (see fig. 437). 



Deposit of Calcium Oxalate This occurs in envelope 



crystals (octahedra) or dumb-bells. 



It is insoluble in ammonia, and in acetic acid. It is soluble 

 with difficulty in hydrochloric acid. 



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

 colourless six-sided crystals (fig. 438). These are rare : they 

 occur only in acid urine, and they may form concretions or 

 calculi. Cystinuria (cystin 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 

 micrococctis urece. This forms ammonium carbonate from the urea. 



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



ITJrea] [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, Ca3(P0 4 ) 2 ; amorphous. 



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

 coffin-lids and feathery stars (fig. 435). 



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

 prisms, in spherules, or in dumb-bells. 



(4) Magnesium phosphate, Mg 3 (P0 4 ) 2 + 22H 2 0, occurs occa- 

 sionally, 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. Very often neutral 

 or alkaline urine will become cloudy when boiled ; this may be 

 due to albumin or to phosphates. It is very important to dis- 

 tinguish between these two, as albuminuria is a serious condition. 

 They may be distinguished by the use of acetic acid, which 

 dissolves phosphates but not albumin. 



A solution of ammonium carbonate (i-in-5) eats magnesium 

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

 phosphate. A phosphate of calcium (CaHPO 4 + 2H 2 O) may 

 occasionally be deposited in acid urine. Pus in urine is apt to 

 be mistaken for phosphates, but can be distinguished by the 

 microscope. 



