This section is from the book "A Treatise On Therapeutics, And Pharmacology Or Materia Medica Vol2", by George B. Wood. Also available from Amazon: Part 1 and Part 2.
The alkaloid has been extracted by Prof. F. Mayer, of New York, by a different process; and was the subject of experiment by Dr. Haigh, of Michigan, with results confirmatory of those obtained in Europe. One-eighth of a grain, thrown into the jugular vein of a dog, produced an instant cessation of respiration, and entire relaxation of the muscles, without the slightest sign of pain. The heart beat tumultuously, but the pulsation gradually became slower, and in two minutes ceased altogether. No contraction of the pupil took place. After death, no congestion was found in the brain, stomach, or bowels; and both sides of the heart were full of blood, though there was none in the aorta. (Am. Journ. of Pharm., May, 1865, pp. 173-8.)
Calabar bean appears to be a direct sedative to the spinal marrow; producing, through its influence on this part of the nervous system, a debility of the muscles, amounting, when it is largely taken, even to palsy; and, when acting as a poison, destroying life probably by causing a paralysis at the same time of the heart and the muscles of respiration. As it occasions these results without loss of consciousness, or any other striking phenomenon of cerebral origin, it differs from the cerebral sedatives in not operating specially on the brain. Besides these properties, it exerts that also of an irritant to the alimentary canal; often vomiting and purging; and in this way not unfrequently saving life, which would be destroyed were the poison retained. Dr. J. Baker Edwards, of Liverpool, reports the cases of seventy children who had eaten of a parcel of the beans brought to that port from Africa, of whom all were vomited, either by the poison itself or by emetics administered, except one; and his was the only case that terminated fatally. The age of the children was mostly under ten; and the quantity taken was from about one-half of one of the kernels to six; the shell having been separated. The nausea and vomiting generally came on in half an hour; the other symptoms, as trembling, dizziness, and loss of power in the limbs, within an hour. From three-quarters of an hour to an hour after taking the poison, the patients were brought under treatment, which consisted mainly of sulphate of zinc and mustard water with a view to vomit. in the fatal case, four kernels had been eaten; emetics failed to act; and the child died of syncope fifteen minutes after admission. The blood was found very fluid; and the heart contained blood fluid or coagulated in all its cavities, showing that death was owing to paralysis of this organ. Ordinarily, in poisoning by Calabar bean, the brain and spinal marrow are not congested, and all the other post-mortem phenomena are merely negative.
As to the milder action of Calabar bean, within the proper therapeutic limits, I do not know that we have much to add to the statement of Dr. Fraser in relation to its effects. According to that writer, a peculiar epigastric sensation is generally first experienced, about five minutes after the taking of the medicine, which gradually increases, and may become almost painful. This continues at intervals, for a considerable time, and is after a little while attended with some dyspnoea, followed by dizziness, and feebleness of the extremities. From about 12 grains of the kernel accidentally taken, Dr. Christison experienced giddiness and a feeling of torpidity, followed by general weakness and faintness, paleness of the surface, extreme weakness and irregularity of the pulse, and indisposition or inability to make any voluntary muscular effort. There was no pain and only a little nausea, and the intellect was normal. in two hours after the bean was swallowed, there was some drowsiness, but no stupor. Dr. Fraser experienced the same effects, with some dimness of vision.
A remarkable property of the bean not yet noticed is that of affecting the pupil, and modifying the power of accommodation of the eye. if a small portion is introduced within the lids, the pupil is speedily contracted, sometimes greatly so; and the focus of vision brought nearer the eye. The influence on the pupil might be ascribed to a sedative action upon the sympathetic nerve centre, whereby the straight fibres are paralyzed, and the circular thus enabled to exercise their full power without resistance; and this is very probably true; but it is not all, for it is asserted that, if the sympathetic nerve supplying the iris be severed, the resulting contraction will be increased by the Calabar bean, which must, therefore, have the power of positively stimulating the contractile function, either by a direct action on the circular fibres, or upon the centres which supply them with nervous influence. it is said that the sight is somewhat dimmed at the moment of the contraction of the pupil. This is ascribable to the diminished quantity of light admitted into the eye; and is said to be less observable, or not at all, when the light is very bright. The property of disturbing the accommodation power of the eye, by which it adapts itself to the variable distance of objects of vision, is ascribable to an irritant action on the ciliary muscle, which is now believed to be the agent of accommodation. By its contraction this muscle probably increases the convexity of the convex lens, and consequently lessens the focal distance more or less according to the energy of its action. The bean, therefore, by stimulating this muscle lessens the focal distance, and thus produces temporary near-sightedness, or diminishes presbyopia when it exists. The discovery of this influence of the bean on the power of accommodation is ascribed to Dr. D. A. Robertson, of Edinburgh. it is a singular fact, established by repeated observation, that the bean acts on the accommodation a few minutes earlier than on the pupil, and ceases sooner.*
All these effects of the bean may be obtained, to whatever part it is applied, whether taken into the stomach, administered as an enema, or injected into the areolar tissue; but it has been noticed, in experiments on the lower animals, that, though the contractile effect on the pupil from local application is very powerful, yet, when it is given by subcutaneous injection, the pupil is uncertainly affected, being sometimes strongly contracted, sometimes less so and in various degrees, and sometimes not contracted at all, or even expanded.