A peculiar alkaloid was indicated in hemlock not long ago by Brandes, half a grain of which killed a rabbit with symptoms like those of tetanus.[[2218]] Other chemists were unable to obtain his results. But the subject was afterwards taken up with success by Geiger, who obtained from the plant a volatile, oleaginous alkaloid, which possesses great energy as a poison.[[2219]] Mr. Morries-Stirling procured from hemlock by destructive distillation an empyreumatic oil similar in properties to those of hyoscyamus, stramonium and tobacco, but producing in animals a state of pure coma.[[2220]]
The effects of hemlock on the animal system have been variously described by different observers. Sometimes they have appeared to be purely soporific like those of opium; at other times they have resembled the effects of belladonna and thorn-apple; and in the lower animals they are quite different, as I have witnessed them, from what they have been described to be in man,—the phenomena being simply those of asphyxia from paralysis of the muscles, without material convulsions and without insensibility. Its irritant action is not well established.
Orfila observed that an ounce of the extract of the leaves killed a dog in forty-five minutes when swallowed, ninety grains killed another through a wound in an hour and a half, and twenty-eight grains another through a vein in two minutes. It therefore acts by entering the blood-vessels. The extract is a very uncertain preparation; the reason of which is, that the alkaloid conia is very easily decomposed in its natural state of mixture by heat or age, being converted into an inert resinoid matter,—that the dried leaves of hemlock contain scarcely any of it,—and that even an extract of the fresh leaves contains little, unless prepared with a gentle heat, yet speedily.[[2221]] The symptoms remarked by Orfila were convulsions and insensibility; and in the dead body the blood of the left cavities of the heart was sometimes found arterial.—The result of my observations is quite at variance with this statement. In various experiments with a strong extract prepared from the green seeds with absolute alcohol, the only effect I could remark were palsy, first of the voluntary muscles, next of the chest, lastly of the diaphragm,—asphyxia in short from paralysis, without insensibility, and with slight occasional twitches only of the limbs, and the heart was always found contracting vigorously for a long time after death. Thirty grains of a soft extract introduced between the skin and muscles of the back killed a rabbit in five minutes, and a five months’ puppy in twenty minutes.[[2222]]
The root is much less energetic than is represented by some authors, and probably varies in this respect at different seasons. I have found that four ounces and a half of juice, the produce of twelve ounces of roots collected in November, had no effect on a dog when secured in its stomach by a ligature on the gullet; and that four ounces obtained from ten ounces of roots in the middle of June, when the plant was coming into flower, merely caused diarrhœa and languor. Orfila had previously observed that three pounds of roots had no effect in the month of April; but that two pounds in the end of May, when the plant was in full vegetation, killed a dog in six hours.[[2223]] The alcoholic extract of the juice obtained from six ounces of roots on the last day of May, I have found to kill a rabbit in thirty-seven minutes, when introduced in a state of emulsion between the skin and muscles of the back; and the effects were analogous to those obtained with the extract of the leaves. The differences depending on season will probably account for various persons having found the juice of the root harmless. Gmelin quotes an instance where four ounces of the juice were taken without injury. He adds another where three ounces of the juice of the herb were swallowed daily for eight days with as little effect. But, as he judiciously observes, other less active plants have probably been sometimes mistaken for hemlock.[[2224]]
The alkaloid, conia, seems to be the active principle of hemlock, and is a poison of extraordinary virulence. On investigating this subject in 1835,[[2225]] I found that it is a local irritant, possessing an acrid taste, and capable of exciting redness or vascularity in any membrane to which it is applied; but that these topical effects are readily overwhelmed by its swift and intense narcotic action. This action consists of swiftly spreading palsy of the muscles, which affects first those of voluntary motion, then the respiratory muscles of the chest and abdomen, and lastly the diaphragm, so as to terminate by causing asphyxia. The paralytic state is usually interrupted from time to time by slight convulsive twitches of the limbs and trunk at the beginning. The muscular contractility is impaired or annihilated by the topical action of the poison, but not by its indirect action through absorption. The heart is not appreciably affected; for it contracts vigorously long after all motion, respiration, and other signs of life are extinct; and it contains after death, not florid but dark blood in its left cavities. The blood undergoes no alteration. The external senses are little, if at all impaired, until the breathing is almost arrested; and volition too is retained. But a contrary inference may be drawn by a careless observer, in consequence of the paralytic state taking away the means, by which in animals sensation is expressed and volition exercised. The action of conia, in short, is confined to the spinal cord; and it acts as a sedative, by exhausting the nervous energy.
Conia is probably a deadly poison to all orders of animals: at least I found it to be so to the dog, cat, rabbit, mouse, frog, fly, and flea; and Geiger killed the kite, pigeon, sparrow, slow-worm, and earth-worm with it. It acts through every texture where absorption is carried on readily, through the stomach, eye, lungs, cellular tissue, peritonæum, or veins; and its activity is in proportion to the speed with which absorption is carried on in the part. It acts therefore through absorption. Its activity is increased by neutralization with an acid, by which it is rendered much more soluble in water. Few poisons equal it in subtility and swiftness. A single drop, applied to the eye of a rabbit, will kill it in nine minutes; and three drops in the same way will kill a strong cat in a minute and a half. Five drops, introduced into the throat of a little dog, began to act in thirty seconds, and proved fatal in one minute. And when two grains, neutralized with thirty drops of weak hydrochloric acid, were injected into the femoral vein of a young dog, it died before there was time to note the interval, so that only two or three seconds at most had elapsed, before all internal signs of life were extinct. This extraordinary rapidity of action seems incompatible with its operation taking place by conveyance of the poison with the blood to the spinal cord. Mr. Blake, as formerly mentioned (p. [15]), denies that its action in this way was ever so swift in his hands, and alleges that he could never observe the interval to be shorter than fifteen seconds. If the reader, however, will consult the original account of my experiment,[[2226]] which was made along with Dr. Sharpey, he will see that we could scarcely be mistaken as to the interval in that instance.
Symptoms in Man.—M. Haaf, a French army-surgeon, has described a fatal case of poisoning with hemlock, which closely resembled poisoning with opium. The subject of it, a soldier, had partaken along with several comrades of a soup containing hemlock leaves, and appeared to them to drop asleep not long after, while they were conversing. In the course of an hour and a half they became alarmed on being all taken ill with giddiness and headache; and the surgeon of the regiment was sent for. He found the soldier, who had fallen asleep, in a state of insensibility, from which, however, he could be roused for a few moments. His countenance was bloated, the pulse only 30, and the extremities cold. The insensibility became rapidly deeper and deeper, till he died, three hours after taking the soup.[[2227]] His companions recovered.
Dr. Watson has briefly described two cases which were fatal in the same short space of time. The subjects were two Dutch soldiers, who, in common with several of their comrades, took broth made with hemlock leaves and various other herbs. Giddiness, coma, and convulsions were the principal symptoms. The men who recovered were affected exactly as if they had taken opium.[[2228]]
When the dose is not sufficient to prove fatal, there is sometimes paralysis, attended with slight convulsions, as in a case noticed by Orfila.[[2229]] More commonly there is frantic delirium. Matthiol has related an instance of this last description, occurring in the cases of a vine-dresser and his wife, who mistook the roots for parsneps Both of them became in the course of the night so delirious that they ran about the house, knocking themselves against every object which came in their way.[[2230]] Kircher, as quoted by Wibmer, tells a parallel story of two monks who became so raving mad after eating the roots, that they plunged into water, imagining that they were turned into geese, and they were affected for three years with incomplete palsy and neuralgic pains.[[2231]] These and some other cases of the like kind, recorded by the older medical authors, must be received with reserve. Independently of other considerations, there is often no certainty that the poison was really the hemlock of modern botanists, and not some other umbelliferous vegetable.
Morbid Appearances.—In Haaf’s case the vessels of the head were much congested; and the blood must have been very fluid, for on the head being opened a quantity flowed out, which twice filled an ordinary chamber-pot. This state of the blood likewise occurred in a case which I examined here some years ago along with Dr. C. Coindet of Geneva. A hypochondriacal old woman took by advice of a neighbour two ounces of a strong infusion of hemlock leaves with the same quantity of whisky, which she swallowed in the morning fasting. She died in an hour, comatose and slightly convulsed. The vessels within the head were not particularly turgid; but the blood was everywhere remarkably fluid. Dr. Coindet subsequently found that a small portion of the infusion prevents fresh drawn blood from coagulating; but I suspect there must have been some mistake here, for a carefully prepared alcoholic extract of very great power, which was used in my experiments alluded to above, had no such effect on blood fresh drawn from rabbits and dogs. On account of this extreme fluidity of the blood, it often flows from the nose, but the skin is much marked with lividity.[[2232]] The fluidity of the blood is nothing more than the result of the proximate cause of death,—slowly formed asphyxia.