Botanical Name hysostigma venenosum
Species: P. venenosum
Synonyms : Ordeal Bean. Chop Nut.
Common Name:Calabar Bean
Habitat: Calabar Bean is native to West Africa, Old Calabar. Has been introduced into India and Brazil.
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.
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. 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 ????, a bladder, and stigma).
The plant came into notice in 1846 and was planted in the Edinburgh Botanical Gardens, where it grew into a strong perennial creeper. It is a great twining climber, pinnately trifoliate leaves, pendulous racemes of purplish bean-like flowers; seeds are two or three together in dark brown pods about 6 inches long and kidney-shaped thick, about 1 inch long, rounded ends, roughish but a little polished, and have a long scar on the edge where adherent to the placenta. The seeds ripen at all seasons, but are best and most abundant during the rainy season in Africa, June till September. The natives of Africa employ the bean as an ordeal owing to its very poisonous qualities. They call it esere, and it is given to an accused person to eat. If the prisoner vomits within half an hour he is accounted innocent, but if he succumbs he is found guilty. A draught of the pounded seeds infused in water is said to have been fatal to a man within an hour.
Constituents: The chief constituent is the alkaloid physostigmine (eserine), with which are calabarines, eseridine, and eseramine. Eseridine is not employed medicinally.
Medicinal Action and Uses:
Chiefly used for diseases of the eye; it causes rapid contraction of the pupil and disturbed vision.Also used as a stimulant to the unstriped muscles of the intestines in chronic constipation. Its action on the circulation is to slow the pulse and raise blood-pressure; it depresses the central nervous system, causingmuscular weakness; it has been employed internally for its depressant action in epilepsy, cholera, etc., and given hypodermically in acute tetanus. Physostigmine Salicylas is preferred for the preparation of eyedrops.
Calabar bean contains physostigmine, a reversible cholinesterase inhibitor alkaloid. The alkaloid physostigmine acts in effect like nerve gas, disrupting communication between the nerves and muscles, and resulting in copius salivation, seizures, loss of control over the bladder and bowels, and eventually loss of control over the respiratory system, causing death by asphyxiation.
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 Richard Fraser has shown that in such cases there comes a time when, if the action of the two drugs is summated, death results sooner than from either alone. Thus atropine will save life if 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.
Poisons and Antidotes: In case of poisoning by the beans the stomach should be evacuated and atropine injected until the pulse quickens. With poisoning by physostigmine the stomach should be washed out with 0.2 per cent of potassium permanganate and atropine and strychnine administered hypodermically.
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