Microscopic Structure—Hemlock fruits differ from other fruits of the order by the absence of vittæ.[1149] In the endocarp, there is a peculiar layer of small nearly cubic cells surrounding the albumen. The cells of the endocarp are loaded with a brown liquid consisting chiefly of conine and essential oil.
Chemical Composition—The most important constituent of the fruits of hemlock Conine or Conia, C₈H₁₄NH, a limpid colourless oily fluid, 0·846 sp. gr. at 12°·5 C. It has a strong alkaline reaction, and boils at 170° C. in an atmosphere devoid of oxygen, without decomposition. It was first observed by Giseke at Eisleben, Saxony, in 1827, recognized as an alkaloid by Geiger in 1831, and more amply studied by Wertheim in 1856 and 1862. To obtain it, an alcoholic extract is submitted to distillation with a little slaked lime. The product should be neutralized with oxalic acid, and the oxalate of conine removed by absolute alcohol mixed with a little ether, oxalate of ammonium being insoluble. The oxalate of the alkaloid shaken with caustic lye and ether, affords the conine, on evaporating the solvent and distilling the alkaloid in a current of dry hydrogen. In the plant it is combined with an acid (malic?), and accompanied by ammonia, as well as by a second, less poisonous crystallizable base, called Conhydrine, C₈H₁₇NO, which may be converted into conine by abstraction of the elements of water. From these alkaloids a liquid non-poisonous hydrocarbon, Conylene, C₈H₁₄, has been separated by Wertheim. Even in nature one hydrogen atom of conine is frequently replaced by methyl, CH₃; and commercial conine commonly contains, as shown by A. von Planta and Kekulé, methyl-conine, C₈H₁₄NCH₃. Lastly there is present in hemlock fruits a third alkaloid having probably the composition C₇H₁₃N.
As to the yield of conine, it varies according to the development of the fruits, but it is at best only about ⅕ per cent. According to Schroff (1870), the fruits are most active just before maturity, provided they are gathered from the biennial plant. At a later stage, conine is probably partly transformed into conhydrine, which however is present in but very small proportion,—about 1¼ per mille at most.
In its deleterious action, conine resembles nicotine, but is much less powerful.
Schiff (1871-1872) has artificially produced an alkaloid partaking of the general properties of conine, and having the same composition; but it is optically indifferent. Conine, on the other hand, we find turns the plane of polarization to the right.
The fruits of hemlock contain also a volatile oil which appears devoid of poisonous properties; it exists in but small quantity and has not yet been fully examined.
Uses—The fruits of hemlock are the only convenient source of the alkaloid conine. They were introduced into British medicine in 1864, as a substitute for the dried leaf in making the tincture. But it has been shown that a tincture, whether of leaf or fruit, is a preparation of very small value, and that it is far inferior to the preserved juice of the herb. It has however been pointed out by W. Manlius Smith,[1150] and his observations have been confirmed by Harley,[1151] that the green unripe fruits possess more than any other part the peculiar energies of the plant, and that they may even be dried without loss of activity. A medicinal fluid extract of considerable power has been made from them by Squibb of New York.
FOLIA CONII.
Hemlock Leaves; F. Feuilles de Ciguë; G. Schierlingsblätter.
Botanical Origin—Conium maculatum L., [see p. 299].