Mr. A. Christison on Cannabis indica. 489 
From these observations then it appears to be undoubted, that the 
only period for collecting the plant in its active state is that time 
when the seeds are beginning to ripen, when therefore the tops of the 
plants are covered with the resinous varnish on which its properties 
depend. 
The resin secreted by Cannabis is insoluble in water, but sokuble in 
rectified spirit; and it may also be separated by oily matters. By 
the action of spirit upon Gunjah the extract of hemp is formed. In 
this country two extraets are used, the one sent from Calcutta, and 
the other prepared in Engiand from the dried plant. The best ex- 
tract presents a dark green colour and is thick and tenacious ; when 
pressed between the fingers it softens and adheres obstinately to them, 
a solvent being necessary for its removal ;—any extract which is found 
to rub down in the fingers should be looked upon with suspicion, and 
will be found to be nearly if not almost totally inert. The finest 
extract I have seen is that prepared by Mr. Robertson, Professor of 
Chemistry at Calcutta, which however is not in the market. Of this 
Mr. Robertson prepared about 30 lbs. ; from a hundredweight of the 
plant he obtained about 8 lbs. of extract. His process consisted in 
passing the vapour of boiling alcohol through the plant packed in a 
cask, an ordinary worm leading from the cask to a receiver ; the pre- 
paring of it cost him much time and trouble on account of the heavy 
duties upon hemp and also upon spirit, and the expense he reckoned 
at 15s. a pound. On these accounts he abandoned the attempt to 
manufacture it in this way, and though he received large orders for 
it from various quarters, he felt compelled to refuse the undertaking. 
Specimens were sent for experiment to various parts of Europe, and 
among others to Edinburgh for Dr. Christison ; this is now four years 
old and retains all its energy, and is much more active than the 
extracts of the shops which are formed by cold percolation. I repeated 
his process on a small scale and found it to be a very complete means 
of exhausting the plant, while at the same time the consumption 
of spirit is less. 
Good extract should give a grass-green tincture with spirit, and 
when the tincture is of a brown colour it is weak or inert. 
Various investigations have been made as to the nature of the resin 
secreted by the leaves of Cannabis, and it has been ascertained that 
a pure resin can be separated retaining the properties of the plant in 
full energy. Gastinell, apothecary at Cairo, has prepared this sub- 
stance, of which he says 2 grs. are as effective as 6 of alc. extract. 
M. de Courtive of Paris says that the resin prepared by him is in 
the dose of 3 gr. as effective as 30 grs. alcoholic extract. He also 
prepared the resin from Paris-grown hemp and from French hemp, 
6 grs. of the first, and 8 to 16 of the second being necessary to pro- 
duce the effect. Surely he cannot have obtained a pure resin, when 
such various doses are required; for the pure principle, from what- 
ever source obtained, should possess exactly the same activity in every 
case. 
The Messrs. Smith of Edinburgh have made careful experiments 
on this subject : they observe that the narcotic action of hemp resides 
