So far as is known, the active principles of hemp are a volatile oil and a peculiar resin called cannabin. That the former has narcotic properties is to be inferred from the effects of the odour of the plant. The latter is a neuter substance, having a somewhat fragrant odour, especially when heated, and a warm, bitterish, subacrid, and balsamic taste. It is insoluble in water, but soluble in alcohol and ether, and from its alcoholic solution is precipitated white by water. M. Jacques Personne has made an experimental investigation into the chemical composition of hemp, from which it may be inferred that this narcotic owes its powers of affecting the system wholly to its volatile oil, and that the resin, when entirely freed from the oil, is inert. M. Personne found the oil to be complex, consisting of two carburetted hydrogens, one of which he proposes to name cannabene, the other hydrate of cannabene. (Journ. de Pharm. et de Ghim., 3e ser., xxxi. 50).

Effects upon the System. The effects of hemp have a certain analogy with those of opium, and, so far as regards the brain, with those of alcohol; showing that all three belong to the same class of agents. But there are also decided peculiarities in the operation of hemp, which distinguish it in a marked degree, from all other cerebral stimulants. It is feeble in its local influence, and but moderately stimulant to the circulation; producing a slight increase in the force of the pulse, with little or none in its frequency. Upon the brain, however, it acts with great energy. Like all stimulants to the cerebral centres, it first exalts, then deranges, and finally diminishes their functions. Hence, as a first effect, there is generally a remarkable exhilaration of the spirits, with a condition of mental reverie, in which a new state of existence seems to open, the most pleasing fancies present themselves, and the thoughts rush along in rapid succession, with little guidance or government from the will. In this state, there is often a disposition to laugh, sing, shout, or dance, or to do some other extravagant act; but, in other instances, the excitement betrays itself in a quarrelsome temper or deeds of violence; and in others, again, there is a quiet internal enjoyment which does not seek any outward expression. The sense of hearing is said, in some instances, to be greatly exalted. A not unfrequent peculiarity of this mental state is that objects seem further off than they really are, and sounds seem to come from a distance. The individual affected often speaks, after recovery, as having felt himself buoyed up, and rising above the surface of the earth. There is, too, a feeling of spiritual or intellectual exaltation, and of superiority to ordinary men. Sometimes there are impressions of duality, as if the patient were at the same time himself and another. Occasionally a species of intoxication is induced, wit!) hallucinations or complete delirium. These effects come on within an hour or two, and are attended with a sense of giddiness, and. as writers generally assert, with aphrodisiac excitement. They gradually subside into a pleasing calm, a feeling of luxurious repose and indolence, during which the senses, particularly that of touch, become more or less obtuse, and general sensibility is so much impaired, that pinching, or other act ordinarily attended with pain is scarcely felt, and causes no uneasiness. Drowsiness soon follows, and, in three or four hours from the taking of the medicine, the person falls into a sleep or stupor, which continues about six or eight hours. During this condition, the pupils are generally dilated, and a state of the muscles is sometimes induced analogous to catalepsy, in which the limbs are perfectly flexible, and may be moved in every direction, but have a tendency to retain any position in which they may be placed. This latter affection, however, has not been noticed by those who have used the medicine in this country and Europe. Dr. O'shaughnessy observed it in several instances among the Hindoos Upon awaking, it is said that, instead of the nausea which is apt to follow the influence of opium, there is often a strong desire for food; and the medicine is believed to have the property of exciting the appetite.

Though thus analogous in its course of action, and in many of its effects to opium, it yet differs from that narcotic remarkably, in one respect, in its operation on the brain. While opium elevates and for a time appears to invigorate the intellectual faculties, hemp, on the contrary, tends to confuse the mind, and induces a purposeless succession of ideas, which, though generally pleasing and even exciting, have no essential connection, and lead to no special result. It does not aid the student in acquiring or the writer or speaker in dispensing knowledge. It is the imagination and feelings which appear to be most highly stimulated, and altogether without the control of reason. The wildest vagaries, the most fantastic images, and the most gorgeous scenes, rapturous to every sense, and often voluptuous under the aphrodisiac influence of the drug, rush in throngs through the fancy, and seem to carry the soul along with them through long periods of passive, but diversified and thrilling adventure.

In its operation on the organic functions, also, hemp differs greatly from opium in several important points. Though, like it, sometimes diaphoretic, it is so in a much less degree; and has none of that tendency to produce constipation of the bowels and dryness of the mouth, or to check the mucous or biliary secretion which so often interferes with the beneficial influence of opium, and so much limits its use. It is, moreover, much less apt to induce nausea, and to leave headache or other disorder behind it.

From alcohol hemp differs in being much less excitant to the vascular system, less brutifying in its effects on the mind and temper, and indis-posed to produce that thickness of speech, and staggering movement, so characteristic of the former stimulant.

There can be little doubt that, in over-doses, it is capable, like the other cerebral stimulants, of proving poisonous; but its effects in this respect have not been fully investigated. A case is reported by Prof. Schroff in which ten grains of an Indian preparation, after giving rise, in an exaggerated degree, to the characteristic effects of the medicine, produced an alarming prostration of the circulation; but the case ended in recovery. (Dublin Quarterly Journ., xxvi. 231.) Alcohol is said to be the most efficient antagonist. (Ann. de Therap., 1865, p. 81.) Among those who use it habitually, it is said ultimately to impair the mental faculties. The remedies, both in its acute and chronic poisoning, would be. the same as those required by opium.

Hemp probably operates, like opium and alcohol, through absorption. Drs. Ballard and Garrod, in their Elements of Materia Medica, state that it imparts an odour to the urine, like that produced by mixing the tincture with water, and somewhat resembling that of the Tonquin bean.