The poisons of which we are about to offer the physiological and chemical history, although more numerous than those which belong to the mineral kingdom, are, notwithstanding, of far less importance in a forensic point of view. With the exception of opium, and some few others, they must be considered as objects of accidental, rather than of criminal poisoning; and even with respect to the former narcotic, it may be said to afford more frequently the means of destruction to the suicide, than to the assassin. The sensible qualities of smell, taste, and sometimes colour, which so eminently characterise deleterious plants, must necessarily render them ill calculated to favour that secresy, which constitutes the indispensable companion of crime; while their bulk, and the pharmaceutical preparation which they require, are alike inconsistent with the hope of concealment. Thus we receive, as it were, from Nature, that protection which art can no longer supply; and the commission of crime is either prevented or discovered, in cases where the powers of chemistry would fail in its detection. The objects which constitute the vegetable kingdom differ from every species of mineral matter, not only in their peculiar organized structure, but in the chemical arrangement of their elements; those of inorganic matter are generally combined in very simple proportions, as one and one, or one and two, &c. whereas in organized bodies, their proportions are much more complicated; and _Dr. Ure_ observes,[394] that such substances derive the peculiar delicacy of their chemical equilibrium, and the consequent facility with which it may be subverted and new modelled, to the multitude of atoms grouped together in a compound; hence too, as _Mr. Children_[395] has observed, is one reason of our utter inability to reproduce even the simplest body of this class, when once its elements have been separated; it is not in the diversity of these elements, but in the manner in which they are grouped, that this peculiarity consists, for, continues the accomplished chemist last mentioned, “vegetable substances seldom contain, as essential, more than three principles—_oxygen_, _hydrogen_, and _carbon_, and sometimes _azote_. With four simple elements then, a brief alphabet for so comprehensive a history! has a bountiful Omnipotence composed the beautiful volume of the living world, where, turn to what page we may, fresh loveliness meets the eye, fresh cause of admiration and delight.”