This section is from the book "Materia Medica And Therapeutics - Vegetable Kingdom", by Charles D. F. Phillips. Also available from Amazon: Materia Medica And Therapeutics: Vegetable Kingdom.
Active Ingredients. - The special and characteristic medicinal substance contained in hemlock is a peculiar alkaloid, called coniine, and known also by the names of conin, conia, and cicutine. It resides in every portion of the plant, but is chiefly abundant in the pericarps of the full-grown but still green fruit, and is separable by distillation with water and caustic potash. It exists in combination with coniic acid. When the leaves are dried, all the conia volatilizes, so that, in this condition, they are useless.
When pure, the alkaloid is, at all ordinary temperatures, an oleaginous, colorless, and volatile liquid, of sp. gr. 0.89, possessed of a strong, penetrating, and stupefying odor, and an acrid flavor, somewhat resembling that of tobacco. The volatile character is made apparent by dropping a small quantity of the alkaloid upon paper, which it will render, in that part, translucent, and as if greasy, the spot disappearing upon subjection of the paper to a slight degree of heat. It burns with a bright flame, giving off, during combustion, a good deal of smoke; the vapor also is inflammable; the boiling point is between 340° and 413° F. At ordinary temperatures, coniine is but slightly soluble in water, requiring 100 times its own volume; but in ether and in alcohol it dissolves readily. With a quarter of its weight of water, it combines, forming therewith hydrate of conia.
The composition of coniine is C8H16N. It is a strong base, and resembles ammonia, not only in being devoid of oxygen, but in many of its reactions. With the vapor of hydrochloric acid it produces copious white fumes, completely neutralizing the acid; and with nitric acid and acetic acid the results are precisely similar. The addition of a small quantity of nitric acid causes coniine to become blood-red. Exposure to the atmosphere resolves it into ammonia and a bitter non-poisonous extractive matter.
A second ingredient in hemlock is the volatile alkaloid called conydria or conhydrine, C8H7NO, discovered by Wertheim, and distinguished from coniine by being solid and crystalline.
A third ingredient, present only in minute quantity, is a volatile oil, which possesses in a high degree the characteristic odor of the plant, but is scarcely at all poisonous. This plainly shows that it is not the active principle of conium; and, further, that in judging of the pharmaceutical value of different preparations of hemlock, no stress can be laid either upon the presence or the absence of the accustomed odor.
Physiological Action. - For our knowledge of the physiological action of conium we are indebted to several observers, who have worked out the subject in a very complete manner. We may dismiss from consideration the statements which were made by the older authors as to the action of conium upon the glandular system, as all these effects have been proved to be imaginary. Their incorrectness is especially demonstrable in regard to the sexual organs. It used to be said that the continued use of conium in large doses would cause the mammae and testes to waste, and destroy sexual power; but the experience of J. Harley, and of many other recent observers, has shown that while conium has the power of repressing unnaturally high sexual excitement, it has no influence upon the natural function, far less any power to injure the glandular structures. The truth is that all statements which were based on the employment of the preparations which were in fashion before the discovery of the alkaloid conia are worthless, for there is every reason to believe that those preparations were quite inert. As to the preparation of hemlock used by the ancient Greeks for the execution of criminals - if our hemlock were really the poison employed (which is perhaps not absolutely certain) - there is every reason to suppose that the fatal drink consisted of the expressed juice, the succus, which has been introduced of late years into our Pharmacopoeias, and is the only one of our officinal forms which has the slightest value. All preparations in which heat is employed are manifestly worthless, in consequence of the great volatility of coniine, as was long ago remarked by Neligan. In speaking, then, of the action of hemlock, we may disregard all results except those that have been obtained by the employment of the alkaloid itself, or the juice, or, it may be added, the non-officinal tincture of the nearly ripe fruit, which J. Harley has shown to contain more of the active principle than any other part of the plant.1 Exact research into the action of conium began with Christison,2 and at once led to important though very incomplete results. Since that time the subject has been investigated in every possible way. Kolliker, Albers, Guttman, Schroff, and many others have investigated the action of coniine upon frogs, upon fish, and upon almost every class of warm-blooded animals; and within the last few years Drs. Fraser and
1 "Old Vegetable Neurotics," p. 92. Also a paper in Practitioner, Oct., 1871. 2 Transactions Royal Soc., Edin., 1835.
Crum-Brown have made most valuable additions to our knowledge by investigating the modifications which are introduced into the action of coniine by sundry chemical combinations. Upon the human subject the most important observations are those of John Harley.
The combined results of numerous modern researches very clearly indicate that coniine is a nerve-poison, with definite and singularly limited affinities. It is one of the most powerful poisons discovered, yet it operates within a very contracted sphere. Normal (i. e., unmodified) coniine acts as a pure paralyzer; upon the motor system it operates through the nerves alone, leaving the spinal cord intact; small doses act exactly like curara, viz., upon the nerve terminals only, but larger doses affect also the motor trunks. The hind limbs are paralyzed first; but the whole system of voluntary motor nerves is ultimately affected, and death comes by cessation of respiratory movements.