This section is from the book "Materia Medica Pharmacy, Pharmacology And Therapeutics", by W. Hale White. Also available from Amazon: Materia Medica Pharmacy, Pharmacology And Therapeutics..
A gummy exudation from Astragalus gummifer Labillardiere, and from other species of Astragalus (nat. ord. Leguminosae).
In narrow or broad bands, more or less curved or contorted, marked by parallel lines, or ridges, white or faintly yellowish, translucent, horn-like, tough, and rendered more easily pulverizable by a heat of 122° F.; 500 C. Very sparingly soluble in cold water, but swells into a gelatinous mass, which is tinged violet (not so deep as the color given by starch by tincture of iodine. Resembling Tragacanth. - Squill, which is thicker and opaque.
The chief constituents are - (1) Bassorin Ch10o5, a gum 33 per cent., only slightly soluble in water, unfermentable. (2) Arabin, 53 per cent., which resembles, but is not identical with the Arabin of Acacia. Precipitated by lead acetate. (3) A little starch.
Tragacanth is contained in several Trochisci.
Tragacanth is a demulcent, and as such may be soothing when applied to a sore throat. Its chief use is to suspend insoluble bodies, as resins, oils, and insoluble powders. The mucilage is better for this purpose than the compound powder (B. P., not official), tragacanth, 1; acacia, 1; starch, 1; sugar, 3;, which, because of its starch, is liable to ferment.