Dioscorea.—Wild Yam.

Fig. 97. 1. Dioscorea villosa, var. glabra. 2. Dioscorea villosa. Photo: Dioscorea bulbifera 1. Preparations: Extract of Dioscorea - Troches of Dioscorea

The rhizome of Dioscorea villosa, Linné.
Nat. Ord.—Dioscoreaceae.
COMMON NAMES: Wild yam, Colic-root, Rheumatism-root.

Botanical Source.Dioscorea villosa, Linné. This is an herbaceous, slender vine, found throughout the United States, but more common in the central and southern portions. The stem is a smooth green twiner, about the size of a goose-quill, twining from the right to the left, over fences, bushes, etc. The leaves are symmetrical and heart-shaped, gradually tapering to a sharp, acuminate point, and are borne on leaf stalks from 2 to 4 inches long. The lower leaves are in whorls of 4 or 5, with intervals of from 6 inches to a foot between, while those on the upper part of the vine are irregularly alternate. The margins of the leaves are entire and wavy in the larger leaves. The veins are generally 9, quite prominent, and gradually diverge from the top of the leaf-stalk. The under side of the leaves is clothed with a thick pubescence. The flowers appear in June or July, are dioecious, very small, and greenish-yellow. The male flowers are in compound loose spikes, with from 3 to 5 slender branches; the perianth is 6-parted, sessile, flattened, and has, near the base, 6 minute stamens. The female flowers are placed at intervals of ¼ of an inch or ½ an inch apart, in simple, drooping, axillary spikes, consisting each, of from 4 to 8 flowers. The ovary is sessile, slender, about ¼ of an inch in length, bearing at the summit a 6-parted, small perianth, and 3 short styles. The female flowers are succeeded by dry, brown fruit, which remains hanging among the limbs of shrubs in winter for some time after the herbaceous stems of the plant have perished. They are sharply 3-angled, and have 3 cells, each cell bearing 2 (or often, by abortion, 1) flat, membranous-winged seed.

Dioscorea villosa, Linné, var. glabra (= male plants of Dioscorea villosa. -Henriette).—This appears to be a distinct variety, chiefly differing from the preceding in the entire dissimilarity of its rhizome. The plant closely resembles the true wild yam in its general shape and in the structure of its leaves, flowers, and fruit. The leaves, however, are entirely glabrous, and are not covered with a short pubescence underneath. The two plants likewise appear to differ in their manner of growth, the D. villosa often growing in dense clumps, while the variety glabra is generally found isolated. From the specific name given to this plant by Linnaeus, it is evident that he was possessed of a specimen of the pubescent kind (or the true wild yam), and we have ventured to apply the designation, var. glabra, to the variety distinguished by smooth leaves and knotty rhizome. Works upon botany recognize only Dioscorea villosa, but it has become necessary to classify the two rhizomae of commerce. Considerable attention has been given by me to the plants, and without an exception the form of the rhizome was indicated by the pubescence of the under surface of the leaf. I am, therefore, led to hold to the foregoing distinctions until a better explanation is given (C. G. Lloyd).

History.—The rhizome of Dioscorea villosa is a favorite therapeutical agent among Eclectic physicians, who have advantageously used it for more than 60 years. It is known as wild yam and colic root. The first specimens employed were from the Dioscorea villosa, with pubescent leaves (Fig. 97), and now known as the true wild yam. About the year 1850, botanic druggists noticed the admixture by root-diggers of the rhizomae represented by (Fig. 97, 1), and for a considerable time rejected it as an adulteration. The diggers insisted, however, that both "roots" were obtained from vines almost identical in appearance (although they can distinguish between them), and finally purchasers were compelled to accept them, more especially as the true rhizomae became very scarce. The late Mr. H. M. Merrell, of Cincinnati, Ohio, to whom we are indebted for this information, stated that the first heavy shipments of the false "wild yam" root to Eastern houses were made about 1860, which article purchasers refused to accept, but after some correspondence, coupled with the fact that the true wild yam root could not at that time be obtained, the parties concluded to receive it. Since then the two rhizomae have been sold indiscriminately, although but little of the original drug is to be found in the market. Eclectic physicians are aware of the difference between these rhizomae, and refuse to use the "false" variety, insisting that it does not possess the medicinal properties, and can not safely be substituted for the "true." In this connection, we invite attention to the accurate engravings of each variety of the rhizomaae in Fig. 97.

The root loses its therapeutical virtues after the first year, and hence should be freshly gathered every year, and carefully dried. Water or alcohol extract its virtues. Several species of Dioscorea yield edible rhizomae, generally known as "yams."

Description.—I. DIOSCOREA VILLOSA, True wild yam. The rhizome of Dioscorea villosa (Fig. 97, 2), appears in market in slender, contorted pieces, from ¼ of an inch to ½ an inch in diameter, and often 2 feet in length. It is oval, being flattened above and below, as it creeps in a horizontal position beneath the surface of the ground. It seldom throws out branches, but occasionally little protuberances project from its sides being from ⅛ of an inch to an inch in length, and about ⅓ as large in diameter as the primary rhizome. They are rounding at the extremity, and seem to indicate an abortive attempt of the rhizome to throw out branches; but they do not send up the vine. Along the upper side of the rhizome are stem-scars, which are about ¾ of an inch apart. The epidermis is brown, thin, and scales off, more or less, upon drying, especially when the rhizome is gathered in the spring, but which is not the case with a good quality of it, when dug in autumn. The internal color of the dry rhizome is whitish, or slightly straw-colored, when gathered in the autumn, but it is often brown when collected early in the season; there is no bark to it. Under a magnifying glass the texture of a broken rhizome appears mealy and perforated with numerous woody bundles. Attached to the lower part of the rhizome, an abundance of strong, wiry-like fibers will be observed. Dioscorea villosa has one of the hardest of rhizomae, it being very difficult to powder or crush. It has no odor, and but little taste beyond a slight acridity after prolonged chewing.

II. DIOSCOREA VILLOSA, var. glabra; False wild yam.—The rhizome (Fig. 97, 1) of this plant resembles that of Collinsonia canadensis more nearly than it does the true D. villosa. It is found as a rough clump of a pound or more in weight when fresh, thickly branched, each branch shooting from the side of the main rhizome at an angle inclining backward and upward. The branches almost touch each other, are as large as the rhizome, and are from 1 inch to 3 inches in length. Along their upper surface are numerous cup-shaped stem-scars, which are about ¼ to ⅓ of an inch in diameter, and so thickly inserted as to intrude upon each other. (The vine of the true Dioscorea villosa, upon the contrary, springs from the main rhizome). The diameter of the rhizome and of the ramifications, is from ½ to ¾ of an inch, and the length seldom more than 6 inches. Internally, the rhizome resembles that of the true wild yam, while the lower portion is, in like manner, covered with stout, fibrous rootlets. The color is generally a very much darker brown.

Chemical Composition.—The virtues of this drug appear to reside in an acrid resin, almost insoluble in water, but readily extracted by alcohol. The so-called dioscorein is not a definite principle of the rhizome, but is simply a dried solid extract, and to call it otherwise is a misnomer. Kalteyer (1888) found a substance closely allied to saponin in considerable quantity in the rhizome. Wild yam contains an abundance of starch.

Action, Medical Uses, and Dosage.—In former editions I have termed this agent an antispasmodic, and solely for the reason that it cures bilious colic. And I can truly say that nearly all remedies have thus been classified, not from any positive knowledge of their action, but from the results following their administration. A change of classification based upon the known action of remedies is certainly desirable, and I am glad to observe that the attention of physicians has already been attracted in this direction. In the absence of any positive knowledge concerning the action of dioscorea, perhaps it would be better to say that it is a specific in bilious colic, having proved almost invariably successful in doses of ½ pint of the decoction, repeated every half hour, or hour. Specific dioscorea may be given in 5-drop doses every 5 minutes. No other medicine is required, as it gives prompt and permanent relief in the most severe cases (Prof. J. King). In fact it is not only of value in bilious colic, but in all forms of colic and other painful abdominal neuroses, and all forms of gastro-intestinal irritation. If it does not relieve in one hour, the medicine should be discontinued. It has allayed the pain incident to the passage of biliary calculi when given with full doses of gelsemium (Webster). It has also proved valuable in painful cholera morbus attended with cramps, in neuralgic affections, in irritable conditions of the nervous system, especially when attended with pain or spasms, in spasmodic hiccough, obstinate and painful vomiting, gastralgia, and in one case of spasmodic asthma Prof. King effected a cure with it after several other means had failed. It will likewise allay nausea, also spasms of the bowels, and, combined with equal parts of the bark of Cornus sericea in decoction, is eminently beneficial in the nausea and vomiting of pregnancy. This root appears to exert an action especially upon enfeebled and irritable mucous tissues that become painful from spasmodic contractions of their muscular fibers; hence its value in bilious colic, in painful dysenteric tenesmus, in dysmenorrhoea the result of spasmodic irritation of the mucous membrane of the cervix uteri, and in spasmodic irritations of the gastric mucous membrane attended with pain, nausea, and vomiting. It is reputed useful in indigestion with hepatic derangement, in chronic hepatic congestion, and in the chronic gastritis of drunkards. It is also useful in after-pains. In ordinary cases the decoction of the root may be given in doses of from 2 to 4 fluid ounces, and repeated every half hour until relief is obtained. By many the infusion or decoction is considered preferable to the tincture. The tincture is said to be a valuable expectorant and diaphoretic, and in large doses produces emesis. Dose of the tincture, from 20 to 60 drops; specific dioscorea, 5 to 40 drops.

Specific Indications and Uses.—Bilious colic; other forms of colic with spasmodic contractions; yellow skin and conjunctiva, with nausea and colicky pains; tongue coated, paroxysmal abdominal pain, and stomach deranged; frequent small, flatulent, alvine passages; colic, with tenderness on pressure; sharp abdominal pain, made worse by motion.

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