This section is from the book "A Treatise On Therapeutics, And Pharmacology Or Materia Medica Vol2", by George B. Wood. Also available from Amazon: Part 1 and Part 2.
This is a concrete exudation from Astragalus verus, and perhaps other species of Astragalus, small prickly shrubs, growing in Anatolia, in Asia Minor, where the drug is collected.
It is in pieces of various shape and size, usually contorted, flat or filamentous, oblong or roundish, extended or rolled up, of a whitish, yellowish, or brownish-white colour, slightly translucent, and of a somewhat horny consistence. it is inodorous and nearly tasteless. its powder is white. in contact with water, it absorbs that fluid, swells up very greatly, and assumes a soft pasty consistence, but does not wholly dissolve. it is composed apparently of two ingredients, one soluble, and resembling if not identical with pure gum, the other softening and swelling up, but not dissolving in water. The latter has been called tragacanthin, but is probably identical with bassorin. Tragacanth is insoluble in alcohol.
In medicine, it is used almost exclusively as an ingredient in lozenges, in the preparation of which it is very useful, by its great tenacity and imperfect solubility, which cause them to dissolve slowly in the mouth. it is also used, in consequence of its viscidity, in the suspension of heavy powders.
Mucilage of Tragacanth (Mucilago Tragacanthae, U. S., Br.) is directed by both the U. S. and Br. Pharmacopoeias. it is prepared by macerating a troyounce of tragacanth with a pint of hot water for 24 hours, then rubbing them into a uniform mass, and straining forcibly through linen. This is very tenacious, and is used in making pills and lozenges, as an adhesive paste, and for the suspension of heavy insoluble powders in water.