Tragacanth is a gum obtained by exudation from the stem of Astragalus gummifer, Labill. (N.O. Leguminosae), a small shrub indigenous to the Turkish Empire and Persia. The drug is also official in the U.S.P. It is produced by the gummosis of the cell walls of the pith and medullary rays, and, swelling by the absorption of water, exerts considerable pressure in the interior of the stem, eventually forcing itself out through cracks or through artificial incisions. It is collected when dry, and graded for the market. That which has been exuded from elongated incisions dries in flakes and is known as "flake" tragacanth, while that which has been pressed through more or less rounded holes, and dries in tears or vermiform pieces, is known as "vermicelli" tragacanth; the inferior qualities are termed "sorts." Two varieties of flake tragacanth are known in commerce, viz., Syrian (or Persian) and Smyrna, the former being alone official in the B.P. Syrian tragacanth occurs in thin, white or pale yellowish-white, horny translucent, ribbon-like flakes, frequently about 25 millimetres long and 12 millimetres wide. They are more or less curved, marked on the flat sides with concentric ridges, and are odourless and tasteless. Tragacanth swells in water to a gelatinous mass, but only about 8 to 10 per cent. dissolves. The gum contains from 9 to 13 per cent. of moisture, and yields, on incineration., about 3 per cent. of ash. Syrian tragacanth contains only a minute trace of starch, but the Smyrna variety contains appreciable quantities; the latter variety is also more opaque and less ribbon-like. Hog gum, or Caramania gum, occurs in yellowish or yellowish-brown, opaque tears or vermiform pieces, which are occasionally whitened by dusting them with lead carbonate; it is said to be obtained from a species of Prunus.
Constituents.—The composition of tragacanth has not yet been satisfactorily ascertained. The part soluble in water appears to consist chiefly of polyarabinan-trigalactan-geddic acid, and yields by hydrolysis arabinose, galactose, and geddic acid. The portion insoluble in water yields under the influence of baryta water isomeric α- and β-tragacanthan-xylan-bassoric acids, which yield by hydrolysis tragacanthose, xylose, and bassoric acid. Traces of starch and of altered cellulose are also to be found in the gum.
Action and Uses.—Tragacanth is employed in pharmacy as a suspending agent in mixtures containing resinous tinctures and heavy insoluble powders, or to emulsify volatile oils. Mucilage of tragacanth and compound powder of tragacanth are used for these purposes, the latter combining the suspending powers of tragacanth and gum acacia, while the starch present tends to prevent agglomeration of the deposit. The mucilage of tragacanth is an efficient suspending agent for the resins of tincture of jalap and tincture of myrrh; it is also employed instead of gum acacia when substances incompatible with the latter are present. In some cases, mucilage of tragacanth answers better than mucilage of gum acacia, or a mixture of the two mucilages may give the best results. It is worthy of note that the addition of mucilage of gum acacia to mucilage of tragacanth produces a thinner mixture than the addition of a similar quantity of water. Mucilage of tragacanth is preferred to mucilage of gum acacia for use in lotions for external use. With essential oils, tragacanth forms a coarse emulsion, which separates on standing, but is readily miscible; the gum should be added to the oil in a dry bottle in the proportion of 1 part of tragacanth to 10 parts of oil; shake, add 72 parts of water and agitate vigorously; then add water in successive portions to the required volume. Tragacanth is also used to form a drying liniment for the skin, which may be used as a basis for the application of ammonium ichthosulphonate, salicylic acid, resorcin, sulphur, etc. A typical preparation, known as Bassorin Paste or Linimentum Exsiccans, is made by mixing in a wide-mouthed bottle 5 of tragacanth powder with 10 of alcohol, adding 70 of water, shaking vigorously, and adding 2 of glycerin with sufficient water to make 100. It dries on the skin, forming a transparent film easily removed by washing. Tragacanth is used sparingly as an excipient to bind pill masses; glycerin of tragacanth is a useful excipient, which should be used in the smallest possible quantity, the mass being well kneaded. A useful excipient for metallic and insoluble salts consists of equal weights of manna and glycerin of tragacanth, beaten together. Glucanth is a pill excipient prepared by mixing 1 of tragacanth in powder with 1 of distilled water and 4 of syrup of glucose.
Also: Pasta Lubricans
- Glycerinum Tragacanthae, B.P.—GLYCERIN OF TRAGACANTH.
- Tragacanth, in powder, 20; glycerin, 60; distilled water, 20. Add the tragacanth to the glycerin, mix, add the water and triturate until the product is homogeneous. Glycerin of tragacanth, used sparingly, is a valuable pill excipient. The mass should be well beaten and as little excipient used as possible, otherwise the pills will be difficult to round, and liable to absorb moisture.
- Mucilago Tragacanthae, B.P.—MUCILAGE OF TRAGACANTH.
- Tragacanth, in powder, 1.37; alcohol, 2.5; distilled water, sufficient to produce 100. Add the alcohol to the tragacanth, shake till the powder is thoroughly diffused, then add sufficient distilled water to produce the required volume, and shake vigorously. Mucilage of tragacanth is employed in mixtures to suspend resinous tinctures (1 of mucilage to 7 of mixture), but with a few exceptions it is not so useful for this purpose as mucilage of gum acacia. The tragacanth mucilage is also used to suspend insoluble powders in mixtures, but like other gums it tends to make the deposit coherent and difficult of diffusion by shaking. It is used instead of mucilage of gum acacia when a suspending agent is required in face lotions and in lotions and mixtures containing salts incompatible with gum acacia.
- Mucilago Tragacanthae, U.S.P.—MUCILAGE OF TRAGACANTH, U.S.P.
- Tragacanth, 6; glycerin, by weight, 18; water, sufficient to produce 100. The glycerin is mixed with 75 of the water and the mixture heated to boiling; the tragacanth is then added and allowed to macerate for twenty-four hours with occasional stirring, sufficient water is added to make the product weigh 100, and it is then strained forcibly through muslin.
- Pulvis Tragacanthae Compositus, B.P.—COMPOUND POWDER OF TRAGACANTH.
- Tragacanth, in powder, 1; gum acacia, in powder, 1; starch, in powder, 1; refined sugar, in powder, 3. Mix the powders intimately. This powder is used as a suspending and emulsifying agent. Dose.—1 to 4 grammes (20 to 60 grains).
The British Pharmaceutical Codex, 1911, was published by direction of the Council of the Pharmaceutical Society of Great Britain.