Contrayerva Pharm. Lond. & Edinb. Contrayerva: the root of a amall plant (dor-ftenia fphondylii folio, dentariae radice, Plum, gen. dorflenia contrayerva Linn.) growing in Peru and other parts of the Spanish West Indies. The root is an inch or two in length, and about half an inch thick; full of knots and irregular tubercles; surrounded on all sides with numerous long tough fibres, most of which are loaded with scaly knobs; of a reddish brown colour on the outside, and pale within. It was first brought into Europe, about the year 1581, by Sir Francis Drake, whence its name Drakena radix.

This root, freed from the fibres, which are much weaker than the tuberous part, has a light aromatic smell; and a roughish, bitterish, penetrating taste, which, as Fuller observes, is not easily concealed by a large admixture of other substances. It is given, as a diaphoretic and antiseptic, in low and malignant fevers, and appears to be one of the mildest and safest of the substances of the pungent kind commonly made use of in these intentions; not being liable to produce, though taken pretty freely, any considerable heat. The dose, in substance, is from five or six grains to half a dram and more; in decoction or infusion, from half a dram to two drams. A compound powder, in which five parts of it are mixed with eighteen of absorbent earths, has long been an officinal preparation, but is now much less employed than formerly.

Contrayerva root gives out its virtue, by the assistance of heat, both to water and rectisied spirit; and tinges the former of a dark-brownish red, the latter of a brighter reddish colour: the watery decoction is very mucilaginous, so as not to pass through a silter. In distillation or evaporation, pure spirit elevates nothing, and water very little of its virtues; the active matter of this root being of the fixt kind, and remaining nearly entire in the watery as well as in the spirituous extracts. The extract: made by rectified spirit tastes strongly of the contrayerva, and leaves in the mouth a durable, glowing, vibrating kind of pungency, like that of peppermint, but far milder: its quantity is about three drams from sixteen of the root. The quantity of watery extract is more than double to that of the spirituous, and its taste pro-portionably weaker.