Calabar bean

Calabar bean
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Scientific classification
Kingdom:	Plantae
Division:	Magnoliophyta
Class:	Magnoliopsida
Order:	Fabales
Family:	Fabaceae
Subfamily:	Faboideae
Genus:	Physostigma
Species:	P. venenosum
Binomial name
Physostigma venenosum

The Calabar bean is the seed of a leguminous plant, Physostigma venenosum, a native of tropical Africa, poisonous to humans. It derives the first part of its scientific name from a curious beak-like appendage at the end of the stigma, in the centre of the flower; this appendage, though solid, was supposed to be hollow (hence the name from φῦσα, a bladder, and stigma).

Growth

The plant is a large, herbaceous, climbing perennial, with the stem woody at the base, up to 2 inches (5 cm) in diameter; it has a habit like the scarlet runner, and attains a height of about 50 feet (15 m). The flowers, resting on axillary peduncles, are large, about an inch long, grouped in pendulous, fascicled racemes pale-pink or purplish, and beautifully veined. The seed pods, which contain two or three seeds or beans, are 6 or 7 inches (15 or 18 cm) in length; and the beans are about the size of an ordinary horse bean but much thicker, with a deep chocolate-brown color.

Toxicology

Calabar bean contains physostigmine, a reversible cholinesterase inhibitor alkaloid.

The main antidote to Calabar bean poisoning is atropine, which may often succeed; and the other measures are those usually employed to stimulate the circulation and respiration. Unfortunately, the antagonism between physostigmine and atropine is not perfect, and Sir Thomas Fraser has shown that in such cases there comes a time when, if the action of the two drugs be summated, death results sooner than from either alone. Thus atropine will save life after three and a half times the fatal dose of physostigmine has been taken, but will hasten the end if four or more times the fatal dose has been ingested.

Historical and medical uses

They constitute the E-ser-e or ordeal beans of the people of Old Calabar, being administered to persons accused of witchcraft or other crimes. In cases where the poisonous material did its deadly work, it was held at once to indicate and rightly to punish guilt; but when it was rejected by the stomach of the accused, innocence was held to be satisfactorily established. A form of dueling with the seeds is also known among the natives, in which the two opponents divide a bean, each eating one half; that quantity has been known to kill both adversaries. Although thus highly poisonous, the bean has nothing in external aspect, taste or smell to distinguish it from any harmless leguminous seed, and very disastrous effects have resulted from its being incautiously left in the way of children. The beans were first introduced into England in the year 1840; but the plant was not accurately described till 1861, and its physiological effects were investigated in 1863 by Sir Thomas R. Fraser. The bean usually contains a little more than 1% of alkaloids. Of these two have been identified, one called calabarine with atropine-like effects, and the other, now a highly important drug, known as physostigmine, used in the treatment of anticholinergic syndrome, myasthenia gravis, glaucoma and delayed gastric emptying.

Mrs. Franklin was poisoned by the Calabar bean in Curtain the last novel both for the author Agatha Christie and her fictional detective Hercule Poirot.

In Jane Kamensky and Jill Lepore's novel Blindspot Edward Easton uses the Calabar bean to poison Samuel Bradstreet and to kill himself.

References

•  This article incorporates text from a publication now in the public domain: Chisholm, Hugh, ed (1911). Encyclopædia Britannica (11th ed.). Cambridge University Press. 
• "The killer bean of Calabar", Laura Spinney, Histories, New Scientist, 28 June 2003.ca:Fava de Calabar