220 DR. EDWARD SCHUNCK ON INDIGO-BLUE. 



in any appreciable quantity in the alcoholic extract of the 

 leaves. 



Some connexion between tyrosine and indigo-blue has 

 frequently been suspected by chemists. Indeed a glance 

 at the formulae of the two bodies will show that some con- 

 nexion is possible, since^ by replacing H by CHj in in- 

 digo-blue and adding 2HjO, we arrive at the formula of 

 tyrosine, thus : — 



CgHjNO + CH, + 2H,0=CgH„N0j. 



Indigo-blue. Tyrosine. 



In order to explain the formation of tyrosine from in- 

 dican, we may suppose the latter to split up into tyrosine, 

 indiglucine, acetic acid, and carbonic dioxide, thus : — 



C,6H„N0.3 + 3H.O = C,H„N03 -f 2(C6H.o06) 



Indican. Tyrosine. Indiglucine. 



-f2(C,H^O0-|-CO,. 



Supposing the tyrosine in this case to have been really 

 formed from indican, the question suggests itself whether 

 the leucine and tyrosine so frequently found in the animal 

 organism as products of disease, may not be derived from 

 some substance similar to indican rather than directly and 

 immediately from albuminoids. 



Polygonum tinctorium. 



This plant has long been known and employed as a 

 source of indigo by the Chinese. According to Stanislas 

 Julien*, who has given translations from Chinese works 

 of various processes for extracting indigo from the leaves, 

 the plant is called in China Lan, the most productive va- 

 riety being termed Tcha-Lan, i. e. the Lan resembling the 

 tea shrub. It was introduced into Europe in the eighteenth 



* Comptes Rendus. t. vii, p. 703 



