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 soluble in 

 rectified spirit ; and it may also be separated by oily matters. By 

 the action of spirit upon Gunjah the extract of he-mp is formed. In 

 this country two extracts are used, the one sent from Calcutta, and 

 the other prepared in England 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 ale. extract. 

 M. de Courtive of Paris says that the resin prepared by him is in 

 the dose of f 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 



