80 



in urine (cold and hot), and in acetic acid. It 

 is soluble in ammonia, from which solution it 

 may be obtained by evaporation in the peculiar 

 crystalline form (fig. 82), visible with the 

 microscope only. Cystin is soluble without 

 effervescence in nitric acid ; from this solution 

 silky crystals of aciculated shape and brilliant 

 white colour may be obtained by evaporation. 

 Treated with nitrate of potass, the sulphur (26 

 per 100 nearly) contained in the cystin passes 

 to the state of sulphuric acid, discoverable by a 

 salt of baryta. Cystin exhales a peculiar phos- 

 phorus-like odour when burned on platina. 



The crystalline form of cystin is the hexa- 

 gonal prism ; the crystal is transparent, more 

 or less regular, and varies considerably in size 

 (fig- 82V 



Fig. 82. 



PRODUCTS, ADVENTITIOUS. 



The neutral phosphate of ammonia and mag- 

 nesia (the only one observed in urine at the 

 moment of emission) occurs in white trans- 

 parent crj-stals of perfectly regular forms, re- 

 ferable to the right rectangular prism (fig. 83). 



Fig. 83. 



Crystals of cystin : some are of much larger size than 

 those represented. 



5. The phosphate of ammonia and magnesia 

 calculus (triple phosphate) is generally of oval 

 or rounded shape, but may be of irregular 

 form ; when constituting the entire substance 

 of a calculus (which is rare), it is of small 

 size usually ; its external colour is whitish ; 

 its surface uneven and crystalline. Internally 

 it is generally granular and opaque, though 

 occasionally laminated and somewhat trans- 

 parent ; in the former case of porous texture, 

 in the latter compact and dense, and of dirty 

 white colour. 



6. The neutral phosphate of lime calculus, 

 remarkable for the smoothness of its exterior, 

 is of pale brown colour, moderate size, and 

 great rarity, so much so that to the chance 

 experience of Dr. Wollaston almost alone are 

 we indebted for what is known of its charac- 

 ters. It is composed of laminae, easily separ- 

 able from each other, and striped trans versely. 



7. The phosphate of ammonia and magnesia 

 and phosphate of lime (mixed phosphates or 



fusible) calculus is of irregular shape, often of 

 large size, white colour, and roughish surface. 

 In the majority of cases its section looks like 

 a piece of chalk of loose texture, being homo- 

 geneous, non-laminated, and minutely porous ; 

 in other instances it is lamellar, and between 

 the laminae minute shining crystals of triple 

 phosphate may often be detected. It marks 

 the fingers or other bodies like chalk. 



Phosphoric acid exists in healthy urine in 

 combination with ammonia and magnesia, in 

 such proportion as to form a perfectly soluble 

 salt. If the proportion of base increases, the 

 salt becomes insoluble, and, according to the 

 amount of excess, is deposited either as the 

 neutral or a bibasic triple phosphate. 



Neutral phosphate of ammonia and magnesia ; crystals 

 of spontaneous formation. 



These crystals are often mixed with amor- 

 phous powder, commonly composed of phos- 

 phate of lime, rarely of urate of ammonia. 

 They are instantaneously soluble in weak 

 acids, and the solution is precipitable by am- 

 monia in the form of the bibasic phosphate. 



The bibasic phosphate of ammonia and mag- 

 nesia does not appear to exist in urine, even 

 the most strongly alkaline, at the moment of 

 emission. But its crystals are developed with 

 the progress of decomposition, and may be 

 obtained from any urine by rapidly adding 

 large quantities of ammonia. Microscopically 

 (fig. 84) these crystals appear aciculated and 

 grouped at angles of 60, so as to resemble 

 a pinnate or bipinnate leaf. 



Fig. 84. 



Bibasic phosphate of ammonia and magnesia. 



Phosphate of lime occurs as an amorphous 

 powder ; very soluble in acids, it does not 

 effervesce under their action, like the urate of 

 ammonia, nor, like that salt, furnish crystals 

 of uric acid under the same circumstances; 

 when the phosphate has been dissolved in an 

 acid, ammonia precipitates a white amorphous 

 mass from the solution. 



8. The xanthic oxide (uric oxide, xanthin, 

 urous acid) calculus is of extreme rarity ; four 

 examples only (analysed by Marcet, Laugier, 

 Stromeyer, and Dulk,) have as yet been met 

 with. The external surface is described as 

 smooth and polished, and of light brown co- 

 lour. Some fragments of the calculus analysed 

 by Stromeyer are preserved in the University 

 College Collection ; their fracture is sharp, 

 their colour pinkish brown ; they are com- 

 posed apparently of easily separable concen- 

 tric laminae, and are very hard ; they become 

 waxy-looking when rubbed. Marcet's speci- 

 men weighed 8 grains, that of Stromeyer 338 

 grains, that of Dulk 7 grains ; those examined 

 by Laugier were very small. In Dulk's case 



