228 DR. EDWARD SCHUNCK ON INDIGO-BLUE. 



rearrange themselves in the order to which their chemical 

 affinities predispose them, and the compound splits up into 

 indigo-blue and indiglucine, this taking place so rapidly 

 that in certain cases it would appear as if the colouring- 

 matter preexisted in the plant. If (to take the simplest 

 case) the leaves as soon as gathered are immersed in cold 

 spirits of wine or in cold ether, the vitality of the cells is 

 thereby destroyed; and the indican contained in them is then 

 in part decomposed, yielding indigo-blue, which remains 

 undissolved, imparting a more or less distinct blue tint to 

 the leaves. When boiling spirit of wine is taken, the 

 indican is extracted before it can undergo decomposition, 

 and dissolves in the spirit. It may be detected in the 

 residue obtained on spontaneous evaporation of the alco- 

 holic extract by its property of yielding indigo-blue on 

 decomposition with acids, as above described. It is pos- 

 sible that the leaves contain some ferment which hastens 

 the decomposition of the indican as soon as vitality has 

 ceased ; but I have no positive evidence to offer in favour 

 of this view. 



I may, in conclusion, describe another experiment, which, 

 though it teaches nothing new, confirms what I have just 

 stated, and is interesting in its way. Having cut some 

 sprigs of Polygonum tinctorium, about six inches long, I 

 immersed the cut ends in dilute hydrochloric acid (con- 

 sisting of one part of acid of specific gravity i ' 1 5 and ten 

 parts of water) , and left them to stand for several days 

 exposed to the sun and air. The acid was gradually 

 absorbed, ascending through the stems, first into the 

 lower leaves, then into the higher ones. The gradual 

 absorption of the acid was distinctly seen by the discolo- 

 ration of the leaves, which commenced at the basis of each 

 leaf and extended towards the apex, the lively green colour 

 being changed into a dirty yellow. After some time this 



