Henbane is an indigenous annual, frequent on waste grounds, and at the sides of roads, particularly on a calcareous soil, flowering in July. The whole of the plant is poisonous when eaten; and in the recent state the odour of the leaves occasions stupor and delirium. The root of this plant when in full vegetation is very powerful; and there are several cases on record, where it has been eaten in mistake for parsnips,[[431]] which it strongly resembles in its sweet and agreeable flavour. Its operation is very analogous to that of opium; producing sickness, stupor, delirium, and coma, with dilation of the pupils.
The pulse, at first hard, gradually becomes weak and tremulous; petechiæ frequently make their appearance, and death ensues. Late experiments have shewn that a peculiar alkaline body constitutes the active principle of this plant, and it has accordingly received, from its discoverers MM. Meissner and Brandes, the name of Hyoscyama.
Boerhaave experienced a trembling and drunkenness, in consequence of having prepared a plaister, into whose composition henbane entered as an ingredient; and the experiments of M. Orfila have shewn that it acts nearly in the same manner, whether applied upon the cellular texture, introduced into the stomach, or injected into the veins. Hence it follows that the active principle of this plant is carried into the circulation, and exerts a remarkable action on the brain and nervous system, producing an extraordinary state of delirium, which is succeeded by stupefaction. The physician will never probably be called upon to investigate a case of wilful poisoning by this narcotic; and should he be summoned to attend a person who, through mistake or accident, had swallowed it, we can hardly anticipate any peculiar mystery which requires elucidation.
There are several other species of henbane, as hyos. alb. aureus, physaloides, all of which are poisonous, although not in the same degree as the hyoscyamus niger, whose history we have just considered.
Prussic Acid. Hydro-cyanic Acid.
The Laurel (Prunus lauro-cerasus) and its distilled water. Bitter Almonds, and their essential oil.
Hydro-cyanic acid exists in a great variety of native combinations in the vegetable kingdom, and imparts to them peculiar qualities, which have been long known. It is, however, only within a few years, that this singular body has been obtained in its separate and independent form[[432]]; indeed it was not until the publication of the celebrated memoir of Gay-Lussac upon this subject, in the year 1815, that its chemical composition was fully understood. In this memoir, it was clearly shewn to consist of a peculiar, gaseous, and highly inflammable compound of carbon and nitrogen, to which the name of cyanogene has been assigned, and hydrogen; the latter body acting as the acidifying principle; whence the term hydro-cyanic acid is very happily contrived to express its composition.
When obtained in its most concentrated form, by the process of M. Gay Lussac,[[433]] it has the following characteristic properties, viz. At ordinary temperatures, it is liquid, colourless, and transparent; possessing an extremely powerful odour, very analogous to that of the blossom of the peach, or bitter almond tree; its taste is, at first, bland and sweetish, but afterwards pungent, bitter, and peculiar. Its extreme volatility is such, that when a drop of it is exposed to the air, on the end of a glass rod, it is rapidly crystallized. The same phenomenon takes place, if a drop be suffered to fall on a sheet of paper. Its specific gravity is ·7055; but, when in a concrete form it is only ·9, while that of its vapour is ·947. If inhaled, it produces almost immediate pain in the head, with deafness, unless very largely diluted with air or water.[[434]] It is decomposed by a high temperature; and by the action even of light it is, in the course of a very short time, resolved into carbonic acid, ammonia, and carburetted hydrogen, a carbonaceous matter remaining behind.[[435]] When brought near a body in a state of combustion, it instantly inflames and burns with a blue light. In water it is sparingly soluble; alcohol dissolves it copiously.
The “medicinal Prussic acid,” as it has been called, as being the preparation lately introduced into medicine,[[436]] differs only from that we have just described, in its degree of concentration. It is, in fact, the Prussic acid of Scheele, and may be considered as equivalent to the preparation of Gay-Lussac diluted with six times its volume, or eight times and a half its weight, of distilled water.
The hydro-cyanic acid has been discovered, in a state of perfect formation, in a variety of vegetables, whose peculiar odour at once announces its presence; such are bitter almonds; the kernels of apricots, cherries, particularly the Cerasa Juliana, and several plums; the leaves of laurel; and peach blossoms; and the bark of the prunus padus, or bird-cherry tree. The only mineral substance, in which hydro-cyanic has yet been detected is the Fer Azuré of Hauy.[[437]] Animal substances, although they do not contain it ready formed, yet, when treated with an alkali at a high temperature, they yield it in great abundance, in consequence of the combination of its elements.