SENA, the leaf of the CASSIA sena of Linnæus, a very common and useful purgative. It is produced from a shrub about a foot high, growing naturally in Egypt and several parts of the Levant. The finest is that from Alexandria, called by the Turks palte, which pays a considerable tribute to the grand signior. The leaves are of an oblong figure, sharp-pointed at the ends, about a quarter of an inch broad, and not a full inch in length, of a lively yellowish green colour, a faint not very disagreeable smell, and a subacid, bitterish, nauseous taste. Some inferior sorts are brought from Tripoli and other places; these may be easily distinguished by their being either narrower, longer, and sharper-pointed; or larger, broader, and round-pointed, with small prominent veins; or large and obtuse, of a fresh green colour, without any yellow cast.
Sena is a very useful cathartic, operating mildly, and yet effectually; and, if judiciously dosed and managed, rarely occasioning the ill consequences which too frequently follow the exhibition of the stronger purges. The only inconveniences complained of in this drug are, its being apt to gripe, and its nauseous flavour. The griping quality depends upon a resinous substance, which, like the other bodies of this class, is naturally disposed to adhere to the coats of the intestines; the more this resin is divided by such matters as take off its tenacity, the less adhesive, and consequently the less irritating and griping it will prove; and the less it is divided, the more griping: hence senna given by itself, or infusions made in a very small quantity of fluid, gripe severely, and purge less than when diluted by a large portion of suitable menstruum, or divided by mixing the infusion with oily emulsions. The ill flavour of this drug is said to be abated by the greater water-sigwort; but we cannot conceive that this plant, whose smell is manifestly fetid, and its taste nauseous and bitter, can at all improve those of senna: others recommend bohea tea, though neither has this any considerable effect. The smell of senna resides in its more volatile parts, and may be discharged by lightly boiling infusions of it made in water; the liquor thus freed from the peculiar flavour of the senna, may be easily rendered grateful to the taste, by the addition of any proper aromatic tincture or distilled water. The colleges both of London and Edinburgh, have given several very elegant infusions of this drug*. The dose of senna in substance is from a scruple to a dram; in infusion, from one to three or four drams.—It has been customary to reject the pedicles of the leaves of senna as of little or no use; Geoffroy, however, observes, that they are not much inferior in efficacy to the leaves themselves. The pods, or seed-vessels, met with among the senna brought to us, are by the college of Brussels preferred to the leaves; they are less apt to gripe, but proportionably less purgative.