CALABAR BEAN
A strong emulsion of Calabar bean, Physostigma venenosum (N.O. Leguminosæ), is used on the West Coast of Africa as a test of innocence in cases of suspected witchcraft. In 1864 some children in Liverpool were poisoned by eating some of these beans, which had been swept out of a ship from Africa on to a heap of rubbish. The poisonous alkaloid is physostigmine or eserine.
Symptoms.—Vomiting, giddiness, irregular action of the heart. The mental faculties are unaffected. The eyes are bright and the pupils contracted; in which latter it differs most strikingly from atropine, hyoscyamine, and daturine, where dilatation of the pupil is the rule. The late Sir R. Christison considered that its primary action is on the heart, causing paralysis of that organ, and that the insensibility and coma are only secondary. Dr. Harley considers that it is not a cardiac, but a respiratory poison. Later experiments have shown that the paralysis produced is due to the action of the drug on the spinal cord and not on the nerve trunks. It appears also that death is due to a failure of the respiration, for the heart in animals has been found still beating for one and a half hours after death. The contraction of the pupil, when locally applied, is probably brought about by its paralytic action on the peripheral sympathetic nerve fibres of the iris; and it is stated that when very large doses of physostigmine are given, the pupils dilate, pointing to oculo-motor palsy. A few drops of the extract placed in the eye cause powerful contraction of the pupil.
Fatal Dose.—Six beans produced death in a boy six years of age.
Chemical Analysis.—The alkaloid eserine should be extracted in the usual way, benzene being used as a solvent in the place of chloroform and ether.
Eserine gives the following chemical reactions:
1. If an aqueous solution of the salt be boiled and then strong nitric acid added, the solution turns a yellowish-orange colour, changed to violet on addition of caustic soda in excess; the violet is discharged on acidulation, but returns on re-alkalising the solution.
2. A solution of eserine in ammonia solution gives a blue residue on evaporation to dryness. Dilute acids produce a red-coloured solution with it, which is fluorescent by reflected light.
3. Bromine water produces a red turbid solution with eserine, which clears on heating.
4. The physiological test—eserine solution instilled into the eye of an animal produces contraction of the pupil.
Treatment.—The stomach should be emptied and washed out by means of the syphon tube, or emetics administered. One-fiftieth to one thirtieth of a grain of atropine sulphate should be administered hypodermically and repeated until the pupils dilate. The tincture of belladonna may be given by the mouth. Stimulants should be given and artificial respiration carried out if required.
CHAPTER XIV
EXCITOMOTORY POISONS
NUX VOMICA STRYCHNINE
Some of the most poisonous known plants belong to the genus Strychnos (N.O. Loganiaceæ).
The Java poison, Upas Tieuté, is a watery extract of S. Tieuté; the basis of the poison used in Guiana, and known as Wourali, Ourari, Urari, or Curare, is the juice of S. toxifera. S. nux vomica, the Koochla tree, produces the nux vomica seeds of commerce; and the bark of the tree has been accidentally substituted for cusparia, or angustura bark, hence it is known as false angustura bark. The substitution is attended with considerable risk, on account of the strychnine which the false bark contains. It may be known by its being quilled, externally covered with white lichenous spots, and the internal surface becoming blood-red when touched with nitric acid. This reaction, which depends upon the presence of an alkaloid, brucine, does not occur when true angustura bark is thus treated.