Senna (Arab, sene), a drug which consists of the dried leaves of several species of cassia, of the order leguminoseoe. In the most familiar plants of this family, as the pea, locust, lupin, and others, the corolla is papilionaceous, and the stamens are united to form a more or less complete tube. In the genus cassia and its allies, the corolla is of distinct and spreading petals, with distinct stamens. The cassias which furnish senna are bushy shrubs, 2 to 4 ft. high, with unequally pinnate leaves, the leaflets of which are unequal at the base and in four to eight pairs; the yellow flowers are in erect axillary racemes, and the broad flattened pods contain six or more seeds. C. acutifolia, with ovate or lanceolate leaves, and C. angustifolia, with narrower and longer leaves, furnish most of the drug, which was in use as early as the 9th century, and still retains its popularity. The principal commercial varieties are the Alexandrian, produced by C. acutifolia, and collected in various districts of Nubia; the Bombay or East Indian, from C. angustifolia of southern Arabia and various parts of India; and the Tinnevelly, which is merely the last named species cultivated in India; the leaves of this are much larger, as the plant is more luxuriant.
The gathering of the first two is done mainly at the close of the rainy season, in September; the bushes are cut and exposed to the sun until the leaves are quite dry, when they are separated by beating with sticks; the whole and broken leaves, the small stems, and the pods are sent to the place of export. Some of it is garbled to remove extraneous matters before it is shipped. Tinnevelly senna, being a cultivated product, is collected with more care, and is a very superior variety of the drug. Senna was formerly much more contaminated by foreign leaves than now; the poisonous coriaria myrtifolia of southern Europe was used to adulterate it; in Alexandria senna argel leaves may be often found, but as this (sarcostemma argel) grows with the senna plants, it is supposed to be an accidental admixture. Senna is an active cathartic, and is largely used both by physicians and in domestic practice; it is usually given in infusion, but sometimes in the fluid extract, tincture, and confection. It contains two bitter principles, and a cathartic acid upon which its activity chiefly depends.
The active principle is readily changed by long continual heat and exposure to the air; hence the infusion should always be made in a covered vessel. - American senna, or wild senna as it is sometimes called, is cassia Marilandica, a perennial herbaceous plant, which grows from New England southward and westward; the root produces numerous erect stems 2 to 4 ft. high, clothed with leaves which have six to nine pairs of lance-oblong, obtuse leaflets, the common petiole bearing at its base a conspicuous club-shaped gland; the bright yellow flowers are in axillary racemes, the two lower petals are the largest, and the anthers of the three upper stamens are deformed and imperfect; the fruit is a narrow, somewhat curved, hairy pod, 3 to 4 in. long. This is a very showy plant, and is now and then seen in gardens, though it is not so well appreciated here as it is in Europe. The leaves are gathered for medicinal use; they possess properties similar to those of the imported senna, but are less active, a third larger dose being required to produce the same effect.
Cassia acutifolia. Plant reduced; leaf and pod of natural size.
American Senna (Cassia Marilandica).