HEMLOCK, Conium, a genus of plants of the natural order umbelliferce, having com pound umbels of small white flowers, small general and partial involucres, the limb of the calyx merely rudimentary, and a compressed ovate fruit with five prominent wavy ridges and no rittce. The best known and only important species is the COMMON HEM LOCK (C. maculatum), which grows by waysides, on heaps of rubbish, and in other similar situations in Britain and on the continent of Europe, in some parts of Asia, and now also as a naturalized plant in North America and in Chili. It has a root somewhat resembling a small parsnip; a round, branched, hollow, bright-green stem, 2 to 7 ft. high, generally spotted with dark purple; the leaves large, tripinnate, of a dark shining green color; the leaflets lanceolate, pinnatifid. All parts of the plant are perfectly destitute of hairs, and it is the only British species of the order umbelliferce which has the stem smooth and spotted with purple. Both the general and partial umbels have many rays. The general involucres consist of several small leaflets; the partial involu eres of three small leaflets, all on one side. The whole plant has a nauseous smell, particularly if rubbed or bruised. The leaves are the only part of the plant employed in medicine. They should be gathered just before the time or at the commencement of flowering, and after the removal of the larger stalks they should be quickly dried by a heat not exceeding 120'. They should then be preserved in perfectly closed tin canis ters. As, however, the dried leaves sometimes yield no conia, conylia, or confine (a volatile alkaloid, which is the active principle in the plant), the fresh leaves are much more certain in their action.
The most important ingredient in hemlock is the conia, which is more abundant in the fruit (seeds) than in the leaves. From 40 lbs. of the ripe but green seeds, Dr. Chris tison obtained two ounces and a half of hydrated couia. As it is volatile, it is obtained by distilling the seeds with water which contains a little potash in solution; conia then passes over with the water in the form of a yellowish oil, and when purified by redis tillation, it is obtained as a colorless, transparent, oily liquid, having a specific gravity of 0.8, a penetrating, hemlock-like odor, communicating a burning sensation when
applied to the tongue, and acting as a very energetic poison. It exhibits a powerful alkaline reaction, and precipitates many metallic oxides from their salts. Strong sul phuric acid causes its compounds to assume first a purple-red and then an olive-green color; while nitric acid gives a blood-red color, fading into an orange. Its composition is represented by the formula CieHi.N. Wertheim has recently discovered a second alkaloid in hemlock, which contains the elements of two equivalents more of water than couia. This substance, whose formula is C,6llr1NO2, he flames conidrin. It may be sublimed in beautiful colorless needles, and is much less poisonous than conia.
Conia has been introduced into the pharmacopeia Norccgica under the name of coniinum, the dose being from one-fortieth to the one-sixtieth part of a grain. The fol lowing illustrations will give an idea of its activity as a poison: One drop placed in the eye of a.rabbit killed it in nine minutes; three drops employed in the same way killed a strong cat in a minute and a half; while five drops poured into the throat of a small dog began to act in thirty seconds, and in as many more, motion and respiration had ceased. It seems to exhaust the energy of the spinal cord, and thus to cause muscular paralysis.
The uses of hemlock in medicine may be arranged under two distinct heads: 1. Those which depend upon its resolvent and alterative powers; and, 2. Those which have reference to its influence over the nervous system. 1. It has been found useful in mammary tumors and profuse secretion of milk, in bronchocele, in enlargements of the liver, spleen, and pancreas, in scrofulous affections, etc., and at one time had a high reputation in cases of cancer. 2. Jt is useful as an antispasmodic and anodyne in whooping-cough, spasmodic cough generally, asthma, neuralgia, etc.