This section is from the book "An Experimental History Of The Materia Medica", by William Lewis.
Turpethum five Turbith. Turbith: the cortical part of the root of a species of convolvulus (Convolvulus Turpethum Linn.) brought from the East Indies, in oblong pieces, of a brown or ash colour on the outside and whitish within: the best is ponderous, not wrinkled, easy to break, and discovers to the eye a large quantity of resinous matter.
This root, on the organs of taste, makes at first an impression of sweetness; but when chewed for some time, betrays a nauseous acrimony. It is accounted a moderately strong cathartic, but does not appear to be of the safest or most certain kind; the resinous matter, in which its virtue resides, being very unequally distributed; insomuch that, as is said, some pieces taken from a scruple to a dram, purge violently, whilst others, in larger doses, have very little effect:.