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CALABAR BEAN

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Originally appearing in Volume V04, Page 963 of the 1911 Encyclopedia Britannica.
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CALABAR See also:BEAN , the See also:seed of a leguminous plant, Physostigma venenosum, a native of tropical See also:Africa. It derives its scientific name from a curious See also:beak-like appendage at the end of the stigma, in the centre of the See also:flower; this appendage though solid was supposed to be hollow (hence the name from 4vQa, a See also:bladder, and stigma). The plant has a climbing See also:habit like the See also:scarlet runner, and attains a height of about 50 ft. with a See also:stem an See also:inch or two in thickness. The seed pods, which contain two or three seeds or beans, are 6 or 7 in. in length; and the beans are about the See also:size of an See also:ordinary See also:horse bean but much thicker, with a deep See also:chocolate-See also:brown See also:colour. They constitute the E-See also:ser-e or See also:ordeal beans of the negroes of Old Calabar, being administeredto persons accused of See also:witchcraft or other crimes. In cases where the poisonous material did its deadly See also:work, it was held at once to indicate and rightly to punish See also:guilt; but when it was rejected by the See also:stomach of the accused, innocence was heldto be satisfactorily established. A See also:form of duelling with the seeds is also known among the natives, in which the two opponents See also:divide a bean, each eating one-See also:half; that quantity has been known to kill both adversaries. Although thus highly poisonous, the bean has nothing in See also:external aspect, See also:taste or See also:smell to distinguish it from any harmless leguminous seed, and very disastrous effects have resulted from its being incautiously See also:left in the way of See also:children. The beans were first introduced into See also:England in the See also:year 1840; but the plant was not accurately described till 1861, and its physiological effects were investigated in 1863 by See also:Sir See also:Thomas R. See also:Fraser. The bean usually contains a little more than 1 % of alkaloids. Of these two have been identified, one called calabarine, and the other, now a highly important See also:drug, known as physostigmineor occasionally as eserine.

The See also:

British See also:pharmacopoeia contains an alcoholic See also:extract of the bean, intended for See also:internal See also:administration; but the See also:alkaloid is now always employed. This is used as the sulphate, which has the empirical See also:formula of (C15H21N3O2)2, H2SO4, plus an unknown number of molecules of See also:water. It occurs in small yellowish crystals, which are turned red by exposure to See also:light or See also:air. They are readily soluble in water or See also:alcohol and possess a See also:bitter taste. The dose is h-h See also:grain, and should invariably be administered by hypodermic injection. For the use of the oculist, who constantly employs this drug, it is also prepared in lamellae for insertion within the conjunctival See also:sac. Each of these contains one-thousandth See also:part of a grain of physostigmine sulphate, a quantity which is perfectly efficient. Physostigmine has no See also:action on the unbroken skin. When swallowed it rapidly causes a See also:great increase in the salivary secretion, being one of the most powerful sialogogues known. It has been shown that the action is due to a See also:direct See also:influence on the secreting gland-cells themselves. After a few minutes the salivation is arrested owing to the constricting influence of the drug upon the See also:blood-vessels that See also:supply the glands. There is also See also:felt a sense of constriction in the pharynx, due to the action of the drug on its See also:muscular See also:fibres.

A similar stimulation of the non-striped muscle in the alimentary See also:

canal results in violent vomiting and purging, if a large dose has been taken. Physostigmine, indeed, stimulates nearly all the non-striped muscles in the See also:body, and this action upon the muscular coats of the See also:arteries, and especially of the arterioles, causes a great rise in blood-pressure shortly after its absorption, which is very rapid. The terminals of the vagus See also:nerve are also stimulated, causing the See also:heart to See also:beat more slowly. Later in its action, the drug depresses the See also:intra-cardiac motor ganglia, causing prolongation of diastole and finally See also:arrest of the heart in See also:dilatation. A large lethal dose kills by this action, but the minimum lethal dose by its combined action on the respiration and the heart. The respiration is at first accelerated by a dose of physostigmine, but is afterwards slowed and ultimately arrested. The initial hastening is due to a stimulation of the vagus terminals in the See also:lung, as it does not occur if these nerves are previously divided. The final arrest is due to See also:paralysis of the See also:respiratory centre in the medulla oblongata, hastened by a quasi-asthmatic contraction of the non-striped muscular See also:tissue in the bronchial tubes, and by a " water-logging " of the lungs due to an increase in the amount of bronchial secretion. It may here be stated that the non-striped muscular tissue of the bladder, the uterus and the See also:spleen is also stimulated, as well as that of the See also:iris (see below). It is only in very large doses that the voluntary muscles are poisoned, there being induced in them a tremor which may simulate ordinary See also:convulsions. The action is a direct one upon the muscular tissue (cf. the See also:case of the gland-cells), sinceit occurs in an See also:animal whose motor nerves have been paralysed by curare. Consciousness is entirely unaffected by physostigmine, there being apparently no action on any part of the See also:brain above the medulla oblongata.

But the influence of the alkaloid upon the See also:

spinal See also:cord is very marked and characteristic. The reflex functions of the cord are entirely abolished, and it has been experimentally shown that this is due to a direct influence upon the cells in the anterior cornua. It is precisely the See also:reverse of the typical action of See also:strychnine. Near the termination of a fatal case there is a paralysis of the sensory columns of the cord, so that See also:general sensibility is lowered. The alkaloid calabarine is, on the other See also:hand, a stimulant of the motor and reflex functions of the cord, so that only the pure alkaloid physostigmine and not any preparation of Calabar bean itself should be used when it is desired to obtain this action. Besides the secretions already mentioned as being stimulated, the bile, the tears and the See also:perspiration are increased by. the See also:exhibition of this drug. There remains only to consider its highly important action upon the See also:eye. Whether administered in the form of the See also:official lamella or by subcutaneous injection, physostigmine causes a contraction of the See also:pupil more marked than in the case of any other known drug. That this action is a direct and not a See also:nervous one is shown by the fact that if the eye be suddenly shaded the pupil will dilate a little, showing that the nerves which cause dilatation are still competent after the administration of physostigmine. Besides the sphincter pupillae, the fibres of the ciliary muscle are stimulated. There is consequently spasm of See also:accommodation, so that clear See also:vision of distant See also:objects becomes impossible. The intra-ocular tension is markedly lowered.

This action, at first sight somewhat obscure, is due to the extreme pupillary contraction which removes the See also:

mass of the iris from pressing upon the spaces of See also:Fontana, through which the intraocular fluids normally make a very slow See also:escape from the eye into its efferent lymphatics. There is a marked antagonism in nearly all important particulars between the actions of physostigmine and of atropine. The details of this antagonism, as well as nearly all our knowledge of this valuable drug, we owe to Sir Thomas Fraser, who introduced it into See also:therapeutics. The clinical uses of physostigmine are based upon the facts of its See also:pharmacology, as above detailed. It has been recommended in cases of chronic See also:constipation, and of want of See also:tone in the muscular See also:wall of the urinary bladder. It has undoubtedly been of value in many cases of See also:tetanus, in which it must be given in maximal doses. (The tetanus antitoxin should invariably be employed as well.) Sir Thomas Fraser differs from nearly all other authorities in regarding the drug as useless in cases of strychnine poisoning, and the question must be left open. There is some doubtful See also:evidence of the value of the alkaloid in chorea. The oculist uses it for at least six purposes. Its stimulant action on the iris and ciliary muscle is employed when they are weak or paralysed. It is used in all cases where one needs to reduce the intra-ocular tension, and for this and other reasons in glaucoma. It is naturally the most efficient See also:agent in relieving the discomfort or intolerable See also:pain of photophobia; and it is the best means of breaking down adhesions of the iris, and of preventing prolapse of the iris after injuries to the cornea.

In fact it is hardly possible to over-estimate its value in See also:

ophthalmology. The drug has been highly and widely recommended in general paralysis, but there remains See also:grave doubt as to its utility in this disease. See also:Toxicology.—The symptoms of Calabar bean poisoning have all been stated above. The obvious antidote is atropine, which may often succeed; and the other See also: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 See also:time when, if the action of the two drugs be summated, See also:death results sooner than from either alone. Thus atropine will See also:save See also: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.

End of Article: CALABAR BEAN

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