An alkaloid obtained from the alcoholic extract of Calabar bean, by dissolving the extract in water, adding bicarbonate of sodium, shaking the mixture with ether, and evaporating the ethereal liquid.

Characters. - In colourless or pinkish crystals.

Solubility. - It is slightly soluble in water, but readily soluble in alcohol and in dilute acids.

Reactions. - The aqueous solution has an alkaline reaction; when warmed with or when shaken with dilute solution of potash it becomes red, and when evaporated to dryness over a water-bath it leaves a bluish residue, the acidified solution of which is beautifully dichroic, being blue and red. Physostigmine causes contraction of the pupil of the eye.