eans without their uses in the economy of nature. It is in the first place not improbable that vegetable poisons serve some purpose in the economy of the plants which produce them. On this point we are still much in the dark, in consequence of the little advancement which has been hitherto made in vegetable physiology. But one purpose of the kind seems to be the perpetuation and extension of such plants, by rendering them unfit for the food of herbivorous animals and frugivorous birds, which by instinct commonly avoid them. In the case of certain poisons of the animal kingdom, their purpose is obviously to preserve the animals which are endowed with them, by enabling them to destroy their prey and their enemies. Another important use to which poisons from every kingdom may be applied, is for the treatment of diseases. A very close connection subsists between medicinal and poisonous action. This is sufficiently shown perhaps by the undoubted fact, that, with very few exceptions, our best medicines are active poisons; and, conversely, that there are few active poisons which have not been turned to account as useful medicines. Besides, in the greater number of instances, the two properties, medicinal virtue and poisonous influence, are plainly nothing else than manifestations of the same action, differing merely somewhat in degree, which is well exemplified by most purgatives and emetics, by opium, hembane, prussic acid, and other anodynes, and by counter-irritants, or substances employed for irritating the skin. In other instances, again, where the poisonous and medicinal actions are to appearance different and unconnected, the existence of some relationship between them seems to be pointed out by the activity of the substances as drugs being proportioned to their energy as poisons. Another purpose to which some poisons are applied is for the destruction of the lower animals for the use of man. In most parts of the world, where the primitive habits of mankind have not been materially modified by civilization, poisons of great energy are familiarly employed for the destruction of game, and in some countries also for killing beasts and birds of prey. In civilized countries they have hitherto been used chiefly for the more ignoble purpose of getting rid of vermin. But they are susceptible of far more important applications of the same nature; which, however, have been as yet entirely overlooked.