Rhus. Rhus spp. Sumac, Sumach.

Rhus.—The genus Rhus contains various species which have the property—probably even without direct contact—of so violently irritating susceptible skins as to produce severe dermatitis. Of these poisonous species there are six which are indigenous to the United States.

R. vernix L. (R. venenata DC.)—Swamp Sumac, Poison Sumach, Poison Elder is our most poisonous species. It is a handsome shrub or small tree, usually ten or fifteen feet high. The bark of the trunk is dark gray, of the branches lighter, of the extreme twigs and petioles pale to deep red. The leaves are pinnate, with three to six pairs of opposite leaflets, and an odd terminal one. These are oblong or oval, entire or slightly sinuate, acuminate, smooth, and, except the one at the end, nearly sessile. The flowers are polygamous, very small, greenish, and in loose or slender axillary panicles. The berries are small, roundish, and greenish white. The tree grows in swamps and low grounds from Canada to Carolina, and flowers in June and July. It was confounded by the older botanists with R. vernicifera DC., of Japan, the Japanese lacquer tree, which has similar poisonous properties. Its activity is said to depend upon urushic acid.

Rhus Michauxii Sargent (R. pumila Michx.. is a rare Southern species, growing in upper Carolina and Georgia, and not more than a foot in height. It is characterized by its pubescent branches and petioles, by its pinnate leaves, with many pairs of oval, nearly acuminate, incised- dentate leaflets, downy beneath, and by its silky fruit. According to Pursh, it is the most poisonous of the genus.

Rhus diversiloba Torrey and Gray (R. Lobata Hooker. is found on our Pacific border. It is there generally known as Poison Oak, and closely resembles the common poison ivy or poison oak (R. Toxicodendron L.)

Rhus Metopium L. (Metopium Linnaea, Engelm.), Mountain Manchineel, Coral Sumac, is a West Indian species, growing also in the "hummock" lands of Southern Florida. It is a small tree, the bark, when wounded, exuding a gum-resin (hog gum) to which medicinal properties are ascribed. The leaves are pinnate with fine leaflets. To the acid red fruit is due the name Coral Sumac. It is exceedingly poisonous.

Rhus Toxicodendron (R. radicans L.., Poison Oak, Poison Ivy, whose fresh leaves were formerly official in the U. S. Pharmacopoeia under the name of Rhus Toxicodendron, U. S., 1890, is a woody vine climbing by numerous aerial rootlets to considerable heights and showing considerable variation. The leaves are 3-foliate, the leaflets being ovate or rhombic, 2.5 to 15 cm. long, entire or sparingly dentate or sinuate, acute or short-acuminate, the lateral sessile or short-stalked, are inequilateral, the terminal ones stalked. The flowers are green, 3 mm. broad, in loose axillary panicles, 2 to 8 cm. long; the fruit globose-oblong, whitish or cream' colored, resembling that of R. Vernix.

The milky juice, of the poisonous species of Rhus, becomes black on exposure to the air, and leaves upon linen or other cloth a stain, which cannot afterwards be removed by washing with soap and water, or by alcohol either hot or cold, but deepens by age. It has been proposed as an indelible ink. Ether dissolves it; applied to the skin it frequently causes inflammation and vesication.

While there is a fairly general agreement that the toxic constituent of the poisonous species of Rhus is a non-volatile substance, there is much evidence that there is a volatile poison also in this plant. (Bessey, A. J. P., 1914, p. 112.) Several authors are inclined to explain the poisoning which results to sensitive persons who pass near Rhus plants without touching them, by saying that the poison resides in the pollen and the plant hairs. The latter may be carried by air currents or may be transported on clothes, or tools, or animals, which after brushing against the plant are able to transfer the poison to susceptible persons. Warren (A. J. P., 1913, p. 548) was unable to detect a poisonous principle in the pollen grains of Rhus Vernix. See also Tschirch and Stevens, A. J. P., 1906, p. 63. Besides the unidentifiable poisonous principle of rhus there is present an iron greening tannin, chlorophyll, wax, fixed oil, resin, sugar, albumen, pectin, gum, starch, and oxalic acid.

The poisonous rhus when taken internally appears to be possessed of narcotic besides irritant properties, vomiting, drowsiness, stupor, dilated pupils, convulsive movements, delirium, and fever having been present in poisoning by them. (Am. J. M. S., April, 1866; also M. Rep., Nov., 1867.) The tincture of rhus has been used especially by homeopathic practitioners in the treatment of sub-acute and chronic rheumatism, and the practice has found imitation.

Some years ago H. C. Wood made extended trials of the remedy, using a homeopathic tincture obtained from a homeopathic pharmacy, in various doses (homeopathic, small, and large), upon a large number of cases of subacute, chronic, and acute rheumatism, in the Philadelphia Hospital, but he was not able to perceive that the patients progressed more rapidly when taking it than when they were simply nursed. The best preparation would undoubtedly be a concentrated alcoholic tincture, made from the green drug; strength of one to four. The dose, of a 25 per cent. tincture given by H. C. Wood was from one to five minims (0.06-0.3 mil), three times a day. The solid extract is an ineligible preparation, owing to the extreme volatility of the active principle of the crude drug.

Rhus canadensis Marsh. (R. aromatica Ait) (Fam. Anacardiaceae).—This indigenous plant, growing in dry soil from Maine and Southern Ontario to Florida and westward, has been highly recommended in the treatment of nocturnal incontinence of urine by a number of clinicians of repute. (See G. H. M. C., 1889; also Annals of Gyncaec., 1890.) For elaborate description of the bark, see Newer Materia Medica. The adult dose is twenty or thirty minims (1.3-1.8 mils) of the fluidextract of the bark, three times a day, given in aromatized solution.

The Dispensatory of the United States of America, 1918, was edited by Joseph P. Remington, Horatio C. Wood and others.