Quassia, or Quassia, L. a genus of trees, consisting of three species, the principal of which is the amara, or Bitter Quassia ; a native of the West Indies and of South America.

The root, wood, and bark of this tree, are all employed in medicine ; but the latter, having a great degree of bitterness, is more efficacious.—Quassia possesses no peculiar odour; but its taste is extremely bitter. It is an excellent tonic, antiseptic, and febrifuge: being one of the least heating drugs, it has been found very serviceable in exciting appetite for food ; expelling flatulency; assisting digestion ; and particularly in removing costiveness, when produced by weakness of the intestines, such as is consequent on sedentary occupations. Dr. Lettsom prescribed it with advantage, in cases of debility after febrile afFections; in dyspepsy arising from intoxication, and in diarrhoeas ; but he directed it with the greatest success, when combined with some absorbent, in the hysteric atony of females. It may be given either in infusion, or in pills composed of the watery extract: the former preparation, however, is generally preferred, in the proportion of three or four drams of the wood, to twelve ounces of water; and which is to be taken in doses of one or two table-spoonfuls, frequently repeated.