This section is from the book "A Text Book Of Materia Medica, Being An Account Of The More Important Crude Drugs Of Vegetable And Animal Origin", by Henry G. Greenish. Also available from Amazon: A Text Book of Materia Medica : Being an Account of the More Important Crude Drugs of Vegetable and Animal Origin.
The bark of the tree contains in the cortex, as well as in the bast, secretory ducts filled with a yellow, resinous emulsion, the two systems of ducts being connected by transverse canals at the nodes.
The gamboge is obtained by making, in the rainy season, a spiral cut in the bark from the height of about 3 metres down to the ground. The emulsion wells out and trickles down the incision into a hollow bamboo placed to receive it. From this it is transferred to smaller bamboos; these are set aside until, in about a month, the gamboge has solidified. It is removed from the bamboo by drying over a fire until the bamboo cracks and can be stripped off. The drug is sold to local collectors, who convey it to Bangkok or Saigon, whence it is exported to Europe, usually via Singapore,
It is occasionally formed whilst soft into cakes of various shapes or into thick sausage-like masses, which are wrapped in leaves, the impression of which they bear on their surface (Saigon gamboge).
The finest qualities of gamboge occur in rolls, 3 to 5 cm. in thickness, and from 10 to 20 cm. in length, nearly cylindrical, solid or hollow in the centre, and marked externally with longitudinal striations derived from the inner surface of the bamboos in which they have been dried. The drug breaks easily, with a smooth, uniform, conchoidal fracture, the freshly fractured surface having a dull gloss and being of a rich reddish yellow or brownish orange colour. It is easily reduced to a bright yellow powder, with little odour, but with an acrid taste.
Thin splinters mounted in oil and examined under the microscope exhibit a ground-mass of gum in which numerous minute granules of resin are scattered accompanied by occasional crystals of calcium oxalate and starch grains derived from the incised tissues.
Rubbed with the wet finger gamboge instantly forms a yellow emulsion. It is almost completely dissolved by the successive action of alcohol and water. The yellow emulsion yielded with water becomes nearly clear and deep orange red on the addition of ammonia.
Gamboge consists essentially of a mixture of 70 to 80 per cent, of resin, with 15 to 25 per cent, of gum.
The resin, formerly known as cambogic acid, is soluble in alcohol, ether, chloroform, benzene, petroleum spirit, etc, as well as in solutions of alkaline hydroxides and carbonates; from its alkaline solutions it is precipitated by acids. From it three organic acids have been separated, viz. a-β and -γ garcinolic acids, the last named being characterised by the red colour of even a very dilute alkaline solution.
The gum is analogous to acacia gum; it is laevorotatory and contains an oxydase enzyme.
Gamboge produces purging and in large doses vomiting. It has been employed as a hydragogue cathartic, but is now seldom used as a medicine.
The chief adulterants are starch, inorganic matter (such as sand, &c), and vegetable debris. These are all easily detected by their insolubility in alcohol and water used successively, or in dilute ammonia.
Pipe gamboge, as above described, is the best variety.
Inferior gamboge breaks with a dull, rough, granular fracture, and the fractured surface, which often exhibits small cavities, is of a dark brownish colour.
Lump or cake gamboge consists of pipe gamboge bent and pressed whilst soft so as to form a cake; or it may occur in irregular lumps which are frequently soft in the interior and often contain abundant visible impurity in the shape of sand, small stones, etc.
Saigon gamboge is occasionally exported from Saigon in short, thick, cylindrical cakes wrapped in palm leaves.
Indian gamboge is obtained in India from G. Morella, Desrousseaux, and resembles Siam gamboge in its essential qualities; it is used as an equivalent of gamboge in India and the Eastern Colonies.