316. Rhus toxicodendron.—Poison ivy. Poison oak.
316. RHUS TOXICODENDRON.—POISON IVY. POISON OAK. The fresh leaves of Rhus rad'icans Linné. Off. U.S.P. 1890. The leaves are trifoliate, the terminal leaflet ovate, stalked, the lateral ones sessile, obliquely ovate. These leaflets are about 100 mm. (4 in.) in length, with margins entire, or coarsely toothed or indented; odorless; taste bitter, acrid, and astringent. The dried leaves are brittle and papery, of a pale green color. Constituents: The fresh leaves abound in an acrid, milky juice, which blackens on exposure to the air, and in contact with the skin causes inflammation and swelling. The acridity is due to what was formerly termed toxicodendric acid, the vapor of which was said to be the cause of vesicular eruptions, but this principle has been found to be, by Pfaff and Balch, an oil, which was given the name, "toxicodendrol." It is said by some authorities (Bessey) that it is volatile. A. B. Stevens shows the principle to be a resin, soluble in a mixture of ether and alcohol, which solvent removes completely the poison from the parts affected. Bessey has shown by test upon himself that, to sensitive persons, the poison may be communicated without handling the plant, and concludes that the principle is volatile. They also contain tannin producing greenish precipitates with iron salts, wax, fixed oil, resin, etc.
Preparation of Toxicodendric Acid.—To bruised leaves add Ca(OH)2; macerate with water; express; add H2SO4; distil. The condensed vapor is a very acrid liquid (see above), which causes the characteristic vesicular eruption of ivypoison.
Local irritant and rubefacient. Used in treatment of eczema, but is no longer in vogue. Dose: 1 to 5 gr. (0.065 to 0.3 Gm.).