4i6 



CYSTIN, LEUCIN, AND TYROSIN. 



out and carefully heated, a dark red colour, which disappears on cooling, is obtained {Gallois, 

 Ktik). [Iuosit gives a green when boiled with Fehling's solution.] 



268 CYSTIN. This left-rotatory body CHi 2 N>S 2 4 , occurs very seldom in large amount 

 in urine' although it seems to be a constituent of normal urine. It may be in solution or in 

 the form of hexagonal crystals (fig. 271, A). It is insoluble in water, alcohol, and ether, but 

 easily soluble in ammonia, from which solution it may be crystallised. According to Baumann 

 and Preusse, there are intermediate products of the metabolism, from which are furnished the 

 materials necessary for the formation of cystin. During normal metabolism these materials 

 undergo further changes, and the sulphur appears oxidised in the urine as sulphuric acid. In 

 rare cases these oxidations do not take place, and then the sulphur appears in the cystin of the 

 urine (Stadthagcn). 



269. LEUCTN = C,;H 13 NO.,. TYBOSrN = C i) H n N0 3 . Both bodies occur in the urine in acute 

 yellow atrophy of the live'r, and in poisoning by phosphorus. (Their formation during 

 pancreatic digestion has been referred to in 170, II.) As the urea excreted is usually 

 diminished at the same time, it is assumed that, in these diseases, the further oxidation of the 



Fig. 271. 



A, crystals of cystin ; B, oxalate of lime 

 c, hour-glass forms of B. 



Fig. 272. 

 a, a, leucin balls ; b, b, tyrosin sheaves ; 

 c, double balls of ammonium urate. 



derivatives of the proteids is interfered with. Leucin, which is either precipitated spontane- 

 ously or obtained after evaporating an alcoholic extract of the concentrated urine, occurs in 

 the form of yellowish-brown balls (fig. 272, a, a), often with concentric markings, or with fine 

 spines on their surface. When heated, it sublimes without fusing. 



Tyrosin forms silky colourless sheaves of needles (fig. 272, b, b). When boiled with mercuric 

 nitrate and nitric acid it gives a red colour, and afterwards a brownish-red precipitate. Piria's 

 Test. When slightly heated with a few drops of concentrated sulphuric acid, it dissolves with 

 a temporary deep red colour. On diluting with water, adding barium carbonate until it is 

 neutralised, boiling, filtering, and adding dilute ferric chloride, a violet colour is obtained 

 (Piria, Stadelcr). 



270. DEPOSITS IN URINE. Deposits may occur in normal and in patho- 

 logical urine, and they may be either M organised" or " unorganised." 



I. Organised Deposits. 



A. Blood : red and white blood-corpuscles and sometimes fibrin (figs. 264-266). 



B. Pus, in greater or less amount in catarrh or inflammation of the urinarv passages. Pus 

 cells exactly resemble colourless blood-corpuscles (figs. 9, 267). Donne's Test. Pour off the 

 supernatent fluid and add a piece of caustic potash to the deposit ; if it be pus it becomes 

 gelatinous, ropy, and more viscid (alkali-albuminate). Mucus, when so acted on, becomes 

 more fluid and mixed with flocculi. 



C. Epithelium of various forms occurs, but it is not always possible to say whence it is 

 derived. 



