In the process of _smoking_ tobacco, the oil is separated, and being rendered empyreumatic by heat, it is thus applied to the fauces in its most active form; whence vertigo, nausea, and all its characteristic symptoms speedily arise upon that occasion; although the system becomes easily habituated to the action of this narcotic, and we continually see a large portion of the community using it daily, in various ways, and in great quantities, as a luxury, without experiencing any other bad effect than that which arises from their inability to relinquish the habit. The well known errhine, _snuff_, is prepared from the dried leaves of tobacco, and possesses all the powers of the plant. The celebrated _Santeuil_ experienced vomiting and horrible pains, amidst which he expired, in consequence of having drank a glass of wine, into which some Spanish snuff had been introduced.[451] _Physiological action of Tobacco._ The deleterious effects of this plant appear to depend on an especial action upon the nervous system; but farther experiments are required to establish through what medium its powers are conveyed to the sensorium. _Orfila_ concludes that the active part of the plant is absorbed, and carried into the circulation. _Mr. Brodie’s_ experiments, however, would lead to the conclusion that it operates through the medium of the nerves; and, what is extremely singular, they shew that the _essential oil_ operates very differently from the _infusion_ of tobacco; for that while the former appears to act exclusively on the brain, leaving the power of the circulation unimpaired, the latter acts on the heart at once, suspending its action even before the animal ceases to respire, and kills by producing syncope. This apparent anomaly at first led _Mr. Brodie_, as he has since informed the author, to suspect the accuracy of his experiments; but their careful repetition rendered this impossible. We suggested to him, whether a probable explanation might not be found in the late chemical results respecting the composition of tobacco, which seemed to shew that this plant possesses two active elements.[452] HEMLOCK. _Cicuta._[453] _Conium[454] Maculatum_ (Pentandria Digynia. _Nat. Ord._ Umbellatæ.)