The fruit of the hemlock plant, commonly called seeds, is roundish-ovate, about one-eighth of an inch long by one-twelfth broad, and composed of two plano-convex parts, easily separable, and each of them with five crenated or notched ribs, running from end to end on the convex surface. They have a yellowish-gray colour, a feeble odour, and a bitterish taste. They are stronger than the leaves and keep better; and, after attaining their full size, are more powerful green than dried. According to the experiments of Hirtz and Hepp, of Strasburg, their strength to that of the leaves is as 10 to 1 (Ann. de Thérap., 1862, p. 22); and it would, therefore, be desirable that they should be generally substituted; as, at best, the medicine is relatively feeble when compared with other narcotics.

Both the leaves and seeds yield their virtues to water, alcohol, and ether; but long boiling with water renders them inert. On destructive distillation, they yield a poisonous empyreumatic oil.

Active Principles of Hemlock. Hemlock yields a volatile oil upon distillation with water, which appears to be destitute of poisonous properties. The principle upon which its activity mainly, if not exclusively, depends is a peculiar volatile alkaloid called conia (also conicin or conein), which, as it exists in the plant, is combined with an acid, probably the coneic, by which it becomes fixed, so that it is not given over with water in distillation. As conia has been introduced into use as a medicine, it will be described among the preparations of hemlock. it was first obtained, in an uncombined state, by Geiger. The existence in hemlock of another alkaloid, discovered by Wertheim, has been announced, for which the name of conhydrin (conhydria) has been proposed; but nothing is yet known of its special therapeutic virtues. it differs chemically from conia only in containing the elements of water. it is probable that the same similarity of physiological effects exists between these alkaloids, as between those of Peruvian bark.

Effects of Hemlock on the System. Hemlock has little local irritant effect; appearing to operate as a direct sedative to the sensibility of the part with which it is brought into contact. in its influence on the system, it is sedative to the nervous centres, especially those of the brain, and indirectly depresses the circulation, but has comparatively little effect on this function. it rarely purges or vomits, and, though said sometimes to act as a diaphoretic or diuretic, does not generally produce these effects, and cannot be depended on for them.

In doses insufficient to produce any very obvious physiological effect, it appears not unfrequently to exert a soothing or composing influence over nervous disorder, and has been thought by many to possess very valuable deobstruent and alterative properties. By the ancients it was supposed to have a tendency to cause atrophy of the mammae and testicles, and to restrain the secretion of milk; and these opinions are not without support from modern writers.

In doses sufficiently large to produce an obvious impression, but still within medicinal limits, it may occasion warmth in the stomach, a sense as of fulness of head, giddiness, headache, dimness of vision, a feeling of weariness in the limbs and of general muscular weakness, faintness, perhaps nausea, without the slightest sign of exhilaration, or elevation of mental function of any kind. The pulse is usually little affected, certainly not increased, but sometimes depressed when the influence is somewhat powerful. in careful experiments, conducted on himself by Dr. Pliny Earle, at the time physician of the Bloomingdale Asylum for the insane, New York, the most prominent symptoms were, first warmth in the stomach, and soon afterwards headache or a feeling of cerebral oppression, slight vertigo, and a sense of weariness or weakness about the knees and elbows, with a want of firmness in the gait. The pulse was but slightly affected; and no drowsiness, or increase of the secretions appears to have been produced. He employed doses of the extract, gradually increased from one to one hundred grains. The effects of the medicine on the head began to be felt in 15 or 20 minutes, were at the height in 35 minutes, and had entirely disappeared in an hour and a half. (Am. Journ. of Med. Sci., N.S., x. 61.)