158 
and then suspended in absolute alcohol. On passing a 
current of carbonic acid gas through the liquid the precipi- 
tate is decomposed, yielding lead carbonate, while the liquid 
acquires a yellow colour. The filtrate is evaporated in a 
current of air, and water is added to the residue, which it 
dissolves for the most part. Sulphuretted hydrogen is 
passed through the filtrate to precipitate the lead in solution, 
and the liquid after filtration is again evaporated. The 
residue is treated with ether, which leaves a portion undis- 
solved. The ethereal solution leaves on evaporation a yellow 
amorphous residue, having all the properties of indican. 
The author made some experiments with the fresh leaves 
of the plant, from which he concludes that the leaf cells 
contain no ready-formed colouring matter with the excep- 
tion of chlorophyll, and that the indigo-blue which is 
formed when the vitality of the cells is destroyed by 
extreme cold, organic lesion, or chemical reagents, is pro- 
duced by the decomposition of indican, which commences 
as soon as the protecting influence of the living cell is 
removed. 
It has long been known that some orchidaceous plants, 
such as Bletia Tankervillice and Gallanthe veratrifolia, yield 
indigo-blue. The author examined the leaves of the former 
plant and obtained a solution, giving the reactions of indican, 
and he is consequently inclined to suppose that the latter 
will be found in all cases to be the source from which indigo- 
blue is derived. 
The author mentions a fact which he thinks may be of 
interest not only to the chemist, but also to the physiologist. 
On one occasion an alcoholic extract of dried woad leaves, 
in which the indican had undergone partial decomposition 
by long standing, yielded on evaporation a quantity of a 
substance which, when purified, was found to have all the 
properties of tyrosine. Though it is possible that the tyro- 
sine may have pre-existed in the plant, the author is inclined 
