CYSTIN, LEUCIN, TYROSIN. 



503 



centimeters are evaporated in a porcelain dish. down to a few drops; then 2 drops 

 of a solution of mercuric nitrate (titration-solution according to J. v. Liebig) 

 are added. A yellow precipitate takes place. If this is spread out and further 

 carefully heated to a point beyond desiccation, a dark-red color appears, which 

 on cooling gradually disappears. 



The sugar may, in rare cases, also give rise to pneumaturia, fermentation by 

 microbes causing the development of carbon dioxid. 



CYSTIN. 



Cystin, C 6 H 12 N 2 S 2 O 4 , is a levorotatory body that occurs normally in [traces 

 in the urine and but rarely in considerable amount. It appears in the form of 

 colorless, six-sided plates (Fig. 162, A), in children also forming concretions. 

 Cystin is insoluble in water, alcohol, and ether; readily soluble in ammonia, after 

 the evaporation of which it crystallizes out. According to Baumann and Preusse, 

 there exist intermediary products 

 of metabolism that contain the 

 material necessary for the forma- 

 tion of cystin. When the metab- 

 olism is normal, these, however, 

 undergo further change ; and their 

 sulphur appears in the urine ox- 

 idized as sulphuric acid. In rare 

 cases this oxidation fails to take 

 place; and then the sulphur ap- 

 pears in the urine as cystin. In 

 cases of phosphorus-poisoning the 

 cystin is increased. 



LEUCIN, C 6 H 13 NOo, AND TY- 

 ROSIN, C 9 H n N0 3 . 



Both of these bodies, whose 

 development has been referred to 

 in the consideration of pancreatic 

 digestion, are present in traces in 

 normal urine. They occur to- 

 gether in somewhat larger amount 

 in association with derangements 

 in the function of the liver-cells 

 (acute yellow atrophy of the liver, phosphorus-poisoning) . As the elimination of 

 urea is generally diminished at the same time, it may be concluded that the liver 

 is the seat of the formation of urea. 



Leucin, which separates either spontaneously in the precipitate or only after 

 evaporation of an alcoholic extract of the inspissated urine, appears in the form 

 of yellowish-brown spheres (Fig. 163, a a) , occasionally with concentric radiation 

 or provided with fine points at the periphery. When heated dry leucin sublimes 

 without fusing. 



Tyrosin forms silky, colorless sheaves of needles (Fig. 163, b 6). If a solution 

 of tyrosin be boiled with Millon's reagent, there results at first a pretty red color, 

 and shortly afterward a deep brownish-red precipitate. If tyrosin is gently 

 heated with a few drops of concentrated sulphuric acid, it is dissolved with the 

 development of a transitory deep-red color. If it now be diluted with water, and 

 barium carbonate be added to the point of neutralization, the mixture boiled 

 and filtered, and dilute iron chlorid added to the filtrate, a violet color appears. 

 Dissolved in hot water, addition of quinone produces a red color. 



FIG. 163. a a, Lcucin-spheres; b b, tyrosin-sheaves; c, double 

 spheres of ammonium urate. 



SEDIMENTS IN THE URINE. 



Both in normal, as well as in pathological urine, precipitates may form at 

 the bottom of the vessel; and these are designated sediments. They are either 

 organized or unorganized. 



