1)K. EDWAHU SCHUNC'K ON INDIGO-BLUE. 22/ 



the preexisteuce of indigo-blue in the plant — though why, 

 if this Avere the case, the colouring-matter should not make 

 its appearance in the unfrozen portions of the leaf, I am at 

 a loss to understand. 



The fact that a fresh leaf of Polygonum tmctorium, if 

 immersed in alcohol or ether, appears blue after the chlo- 

 rophyll has been removed, has also been considered to 

 prove the preexistence of indigo-blue in the cells. This 

 phenomenon is always observed when the leaves are im- 

 mersed in cold alcohol, and more distinctly when ordinaary 

 spirits of wine are taken than with absolute alcohol. A 

 very simple experiment suffices, however, to prove that 

 in this, as in all the other cases, appearances are deceptive. 

 If freshly gathered leaves of Polygonum iinctorium are 

 plunged at once not into cold, but into boiling alcohol, the 

 whole of the colour is soon removed, the leaves retaining 

 only a faint yellow tinge. On now simply evaporating 

 the green alcoholic liquid, not a trace of indigo-blue will 

 be found in the residue. It is therefore absolutely certain 

 that the leaves contain no ready-formed colouring-matter ; 

 for so stable a body as indigo-blue could not possibly be 

 decomposed or be made to disappear by the action of 

 boiling alcohol only. It must necessarily appear either in 

 the alcoholic extract of the leaves or in the residual portion 

 left by the alcohol. 



A very simple explanation offers itself, I think, for all 

 tbe phenomena hitherto observed. Indican, the mother 

 substance of indigo-blue, is a bodj^ the molecules of which 

 are in a state of unstable equilibriimi. As long as it is 

 contained within the cells of the plant the vitality of the 

 cells keeps it in its original unchanged condition. As 

 soon, however as this vitality is destroyed (whether by 

 organic lesion, by extreme cold, or any other means), 

 the indican begins to undergo decomposition, the molecules 



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