192 



TYROSIN. 



NH.CO 

 in the form of tyrosin-hydantoin * OH . C 6 H 4 - C 2 H 8 ' 



X CO. NH 

 This substance is the anhydride of tyrosin hydantoic acid 2 



OH . C 6 H 4 - C 2 H 3 (NH . CO . NH 2 ) COOH. 



and analogous to the similar compounds excreted after the ingestion 

 of sarkosin and taurin. (See pp. 141, 143.) It yields tyrosin, am- 

 monia, and carbonic dioxide when heated with baryta in sealed 

 tubes. 



4. Kynurenic acid. C 10 H 7 N0 8 . [C 9 H 5 N . OH . COOH.] Oxy- 

 chinolin-carboxylic acid. 



This acid occurs characteristically but in variable amounts in 

 the urine of dogs, but does not appear to have been found normally 

 in that of man. It was first described by Liebig. 3 It is most 

 readily separated horn fresh urine by precipitation with phospho- 

 tungstic acid after the addition of hydrochloric acid ; it is then 



FIG. 33. CRYSTALS OF KYNURENIC ACID. (After Kiihne.) 



liberated from the precipitate by the action of baryta. 4 It may 

 also be obtained by concentrating the urine to one-third of its 

 bulk, acidulating with hydrochloric acid and allowing it to stand 

 in a cool place for several days until the separation of the acid is 

 complete. 5 It may be separated from admixed uric acid by solu- 

 tion in dilute ammonia. It is practically insoluble in cold water, 

 slightly so in boiling water, and readily soluble in hot alcohol and 



1 Blendennann. Ibid. Bd. vi. (1882), S. 234. 



2 Jaffe', Ibid. Bd. vn. (1883), S. 306. 



3 Liebig's Annalen, Bd. 86 (1853), S. 125, Bd. 108 (1858), S. 354. 



4 Hofmeister, Zt. f. phi/siol. Chem. Bd. v. (1881), S. 67. Cf. Brieger, Ibid. 

 Bd. iv. S. 89. 



6 Schmiedeberg u. Schultzen, Liebig's Annalen, Bd. CLXIV. (1872), S. 155. 



