Spec. Plant. Willd. iii. 1256. Cl. 17. Ord. 4. Diadelphia Decandria. Nat. ord. Leguminosae. G. 1379. Legume generally two-celled, gibbous. Species. A. verus. True Astragalus. Olivier, Voy. dans l'Empire

Ottoman, v. 342. pl. 44. A. creticus. De Candolle Astragologi. Officinal. Tragacantha, Lond. Astragali Tragacanthae gummi, Edin. Astragalus Creticus; Gummi, Dub. Tragacanth.

Syn. Gomme Adragant (F.), Traganth (G.), Gom Drangant (Dutch), Draganti (I.), Gomo Tragacantho (S.), Alcatira (Port.), Sumegh ulkassael (Arab.), Xuttivah (H.), Vaeberno cottuypisin (Tarn.).

The shrubs, for they are probably many, which yield Tragacanth, are natives of the north of Persia; and there are yet just reasons for doubting whether the Astragalus verus is the only one. This plant is called Kurn, in Persia, and flowers in July and August. It rises two or three feet only in height, on a stem about an inch in thickness; with many branches closely crowded together, and covered with imbricated scales and spines, formed from the petioles of the former year. The leaves, which scarcely exceed half an inch in length, are composed of six, seven, or eight pairs of opposite villous, stiff, pointed leaflets; and the midrib is terminated with a sharp yellowish point. The flowers are small, yellow, and proceed from the axillae of the leaves, with cottony bractes. The calyx is five-toothed, and shorter than the corolla, which is papilionaceous.1

The gum exudes in summer, more or less copiously, according to the heat of the weather, in tortuous filaments, which are allowed to dry on the plant before being collected. A large portion of the Tragacanth collected in Persia is sent to India, Bagdad, Bussorah, and Russia: but what we receive is sent to Aleppo, whence it is exported, packed in cases.

Qualities.-Good Gum Tragacanth is inodorous; impres-ing a very slightly bitter taste as it softens in the mouth. It has a whitish colour; is semi-transparent, and in very thin, wrinkled, vermiform pieces: brittle, but not easily pulverised, except in frosty weather, or in a warmed mortar. Its sp. gr. is 1.384. It swells and softens in water, but does not form a homogeneous fluid mucilage, unless triturated after digestion with a large portion of water : but when the water is acidulated with any of the mineral acids, a small portion of it is dissolved. Bucholz regards the insoluble part as a peculiar substance, which he names Tragacanthiu. Tragacanth is wholly insoluble in alcohol and ether. Dr. John has given the name of Cerasin to this species of Gum, from its being exuded pure from the Cherry-tree, Prunus cerasus. Its mucilage differs from that of Acacia gum in being precipitated by the acetate of lead, sulphate of copper, nitrate of mercury, and muriate of tin; and not by silicated potassa2, nor by the persulphate of iron.

It also contains some fecula: it is tinted blue by iodine.

Medical properties and uses.-Gum Tragacanth is demulcent; and may answer the purposes of the Acacia gum; being even better adapted for allaying tickling cough, and sheathing the fauces in catarrhal affections, owing to its greater viscidity. It is chiefly, however, employed for pharmaceutical purposes. The dose is grs. x. to 3 j. or more.

Officinal preparations.-Mucilago Astragali Tragacanthce, E.D. Pulvis Tragacanthae comp. L. Confectio Opii, L. D.

Before Oliver suggested that the species of Astragalus above described yields the Tragacanth of commerce, this gummy substance was supposed to be yielded by the A. Tragacantha of Linnaeus, on the authority of Tournefort; or the A. gummifera, on that of M. de la Billardiere. Perhaps all these species yield it, although the A. verus or the A. creticus be that from which it is more generally procured. Sieber affirms that the true tragacanth plant is the A. aristatus, which grows upon Mount Ida, where the Tragacanth is gathered in great abundance. The Kuttirah gum from India has been found not to answer the purposes of the ordinary Tragacanth.

2 Bostock, Nicholson's Journ. lviii. 30.