Botanical name: 

The root and prepared resin of Thapsia garganica, Linné.
Nat. Ord.—Umbelliferae.

Botanical Source.—This plant is a herbaceous perennial, from 2 to 4 feet high. It has a round, smooth stem, and 3 pinnately-compound leaves, which are borne on sheathing leaf-stalks. The flowers are in large, compound umbels, and the yellow petals are elliptical, and with an inflexed point. The fruit consists of 2 dorsally-compressed carpels, which are 9-ribbed, with the 2 side-ribs winged. The root is large, from 1 to 2 feet long, and from 2 to 3 inches in diameter at the thickest part.

History and Chemical Composition.—This plant is a native of Spain and other parts of southern Europe, and also found in northern Africa. According to Dioscorides, it derives its Dame from the island of Thapsos, in which it was first discovered; in the time of Theophrastus, it was found in abundance on the promontory, called Gargano, hence its species name of Garganica. It contains an acrid, milky juice when fresh, and yields a resin when dried The root is the part employed in medicine, and has long been in use with the Arabs. The resin of the African variety (Thapsia Sylphium of Viviani) is a strong irritant, both the resin and dried root being exported from Algeria in considerable amounts. The resin is obtained by extracting the dry root with alcohol, distilling the tincture, and washing the residue with water (Reboulleau and Bertherand, 1857). It is soluble in alcohol, ether, and carbon disulphide; becomes plastic at 16° C. (60.8° F.), has an amber-yellow color, and a specific gravity somewhat greater than that of water. It is said to be a component of a plaster made in France, and sold under the name Thapsia Plaster. Desnoix prepares this plaster as follows: Rosin, 15 parts; elemi, 12 ½ parts; yellow wax, 18 parts; turpentine, 5 parts; resin of thapsia, 3 ½ parts. Melt the rosin, elemi, and wax together, and then add the turpentine and thapsia resin. Strain through linen, and spread upon leather (Dorvault, L'Officine, 1872, p. 883). Thapsia also contains an irritating volatile substance, which affects the exposed skin of those distilling the alcoholic tincture, and who have, consequently, to exercise much care during the operation. M. Yvon (Pharm. Jour. Trans., Vol. VIII, 1877, p. 162) found Thapsia Sylphium to possess this property in a marked degree, while T. garganica did not exhibit it. Canzoneri (1883) obtained from the dried root of Thapsia garganica, by percolation with ether, a syrupy acid resin of strongly vesicating properties. It was differentiated into liquid octoic or caprylic acid (C8H16O2), crvstallizable thapsic acid (C16H30N4), and a non-nitrogenous, neutral, vesicating substance (Amer. Jour. Pharm., 1884, p. 325).

Action and Medical Uses.—The properties of this plant reside in its resin, which has been employed as a vesicating or irritating plaster in rheumatic, neuralgic, and other local pains, and in all cases in which a counter-irritant is indicated. According to its mode of preparation, and the length of time it is allowed to remain upon the part, its effect may be varied from that of a slight redness to the production of an intense irritation with the formation of vesicles; its action being, in this respect, similar to that of euphorbium, croton oil, mezereon, and other counter-irritants. It is more commonly employed in combination with other agents, to modify its more active effects. The tincture of the resin may be painted upon oilcloth, adhesive plaster, or other material, and used as a local counter-irritant. Internally, this agent is not employed, though it is stated to possess emeto-cathartic properties.

King's American Dispensatory, 1898, was written by Harvey Wickes Felter, M.D., and John Uri Lloyd, Phr. M., Ph. D.