192 TYROSIN. 



pitate. The test in its original form was applied by heating with a 

 solution of mercuric nitrate in presence of nitrous acid 1 . 



Piria's reaction 2 . If tyrosin is moistened on a watch-glass with 

 concentrated sulphuric acid and warmed for five or ten minutes on 

 a water bath, it turns pink owing to the formation of tyrosin-sulphonic 

 acid C 9 H 10 (S0 2 OH) NO 3 + 2H 2 O. This is then diluted with water, 

 warmed, neutralised with barium carbonate, and filtered while hot. 

 The filtrate yields a violet colour on the careful addition of very dilute 

 perchloride of iron. The colour is readily destroyed by any excess of 

 the iron salt 3 . 



The remarks made on p. 150 on the optical properties of leucin, 

 apply also to tyrosin 4 . 



When tyrosin is subjected to putrefactive decomposition it yields paraoxyphenyl- 

 acetic acid OH. C 6 H 4 -CH 2 . COOH., paraoxyphenyl-propionic (hydroparacumaric) 

 acid OH . C 6 H 4 - CH 2 . CH 2 . COOH., ,8-phenylpropionic - (hydrocinnamic) acid 

 C 6 H 6 . CH 2 . CH 2 . COOH., phenol, C 6 H 5 . OH., and parakresol CH 3 . C 6 H 4 . OH. 5 

 These substances occur normally in small and variable amounts in urine and are 

 increased in quantity in this excretion by the administration of tyrosin. Their 

 presence is without doubt chiefly due to putrefactive processes occurring in the 

 alimentary canal in correspondence with the facts that the bodies in question are 

 found most markedly in the urine of herbivora, in increased quantity in that of men 

 under a vegetable diet, and largely disappear under the influence of drugs such as 

 calomel which lessens or prevents the occurrence of putrefactive changes in the 

 intestine 6 . In the absence of these putrefactive processes tyrosin when admin- 

 istered in not excessive amounts is apparently completely oxidised and does not, as 

 frequently stated give rise to any increased output of urea 7 . In large doses tyrosin 



' X NH.CO 



reappears externally in the form of tyrosin-hydantoin 8 OH . C 6 H 4 - C 2 H 3 | . 



X CO.NH 

 This substance is the anhydride of tyrosin hydantoic acid 9 



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 sarkosiu and 

 taurin. (See pp. 141, 143.) It yields tyrosin, ammonia and carbonic dioxide when 

 heated with baryta in sealed tubes. 



1 Liebig's Annal. Bd. LXXXVII. (1853), S. 124. 



2 Liebig's Annal. Bd. LXXXII. (1852), S. 231. 



3 For other less important reactions see Wurster, Centralb. f. Physiol. Bd. 

 i. (1887), S. 194. Udranszky, Zt. f. physiol. Chem. Bd. xn. (1888), S. 355. 



4 For details see Mauthner, Monatsb. f. Chem. Bd. in. (1882) also Sitzb. d. 

 Wien. Akad. Bd. LXXXV. (1882), April-Hft. Schulze, Zt. f. physiol. Chem. Bd. 

 ix. (1885), Sn. 98, 109. Lippmann. Ber. d. d. chem. Gesell. 1884, S. 2838. 



5 Weyl, Zt. f. physiol. Chem. Bd. m. (1879), S. 312. Baumann, Ibid. Bd. 

 iv. S. 304. Schotten, Ibid. Bd. vn. (1882) S. 23. Salkowski, E. u. H. Ibid. S. 450. 

 Baumann, Ibid. S. 553. 



6 Baumann, Zt. f. physiol. Chem. Bd. x. (1886), S. 129. 



7 Schultzen u. Nencki, Zt. f. Biol. Bd. vra. (1872), S. 124. Kussner, Inaug. 

 Diss. Konigsberg 1874. Brieger, Zt. f. physiol. Chem. Bd. u. (1878), S. 241. 

 Bohmann, Berl. klin. Wochensch. 1888. Nrn. 43, 44. Cohn, Zt. f. physiol. 

 Chem. Bd. xiv. (1819), S. 200. 



8 Blendermann, Ibid. Bd. vi. (1882), S. 234. 



9 Jaffe, Ibid. Bd. vn. (1883), S. 306. 



