Senna, or Cassia senna, L. an exotic shrub cultivated in Persia, Syria; and Arabia, whence its dried leaves are imported. They are of a yellowish-green colour, have a faint, though not unpleasant smell; and a sub-acrid, bitterish, nauseous taste. - There is a spurious sort of this drug obtained from Tripoli, and other places; but the fraud may be easily detected; as the latter is of a fresh green colour, without any yellow shade.

Senna is an useful purgative, operating mildly, though effectually ; and at the same time promoting the secretion of urine. Its ill flavour may be corrected, by slightly boiling the leaves in water; and, being apt to occasion gripings, it should be conjoined with any proper aromatic tincture, or distilled water; dried lemon or orange peel; fennel or aniseeds: - to increase its effects on the bowels, manna, rhubarb, tamarinds, tigs, or prunes, are generally added. In a state of powder, the dose of senna is from a scruple to a dram; but, when taken in decoction, from one to three or four drams are required. - On importation, it pays 6 3/4d. per lb.