150 



CYSTIN. 



the body has been already pointed out ( 488). It will be further 

 considered under urea. 



AMIDO-ACIDS OF THE LACTIC SERIES. 



Cystin. (C 8 H 6 NS0 2 ) 2 . [S . C(CH 8 )(NH 2 ) . COOH] 2 . 

 pholactic acid. 1 



Amido-sul- 



Is the chief constituent of a rarely occurring urinary calculus 

 in men and dogs. It may also occur in renal concretions, and in 

 gravel, and is occasionally found in urine, from which it separates 

 out as a greyish sediment on standing. It is prepared from this 

 sediment, or better still from cystic calculi, by solution in am- 

 monia. This solution is then allowed to evaporate spontaneously 

 and yields the cystin in regular, colourless, six-sided tables of very 

 characteristic appearance. Cystin may be separated from urine 

 by taking advantage of the formatioa of a sodium salt of ben- 

 zoyl-cystin when it is shaken up with a few drops of benzoyl- 

 chloride. 2 



FIG. 13. CYSTIN CRYSTALS. (After Funke.) 



Cystin is insoluble in either water, alcohol, or ether, readily 

 soluble in ammonia, differing in this respect from uric acid, also 

 in many alkaline carbonates and in mineral acids. Its solutions 



1 The constitution of cystin has been variously stated by different authors, and 

 will only be known with" certainty when its synthesis has been accomplished. 

 Slightly different formulae have been assigned to it, containing respectively 5, 6, and 

 7 atoms of hydrogen. The literature is fully quoted by Kiilz, Zt. f. Biol. Bd. xx. 

 (1884), S. 1. Cf. Baumann, Zt. f. physiol. Ch'em. Bd. vni. (1884), S. 299. 



2 Goldmann u. Baumann, Zt. f. phi/siol. Chem. Bd. xn. (1888), S. 254. Udranskv 

 u. Bamnann, Ibid. Bd. xv. (1891), S. 87. 



