_Foderé_, in the fourth volume of his _Medicine Legale_, arranges poisons according to their action on the living system, and which, with a slight alteration in the order of the classes, has been adopted by _Orfila_, and most other writers on Toxicology. Poisons are thus reduced into six classes: viz. 1. CORROSIVE or ESCHAROTIC, as the _Preparations of Mercury_, _Arsenic_, _Antimony_, _Copper_, _Tin_, _Zinc_, _Silver_, _Gold_, and _Bismuth_; the _concentrated Acids_, and _caustic Alkalies_, and _Earths_; _Cantharides_; _glass and enamel powder_; _diamond dust_.[219] 2. ASTRINGENT POISONS, of which the _preparations of Lead_ constitute the only species. 3. ACRID or RUBEFACIENT POISONS, which, with a few exceptions, are furnished by the vegetable kingdom, as certain _drastic purgatives_, _Hellebore_, _Euphorbium_, &c. 4. NARCOTIC POISONS, _Opium_, _Henbane_, the _Cherry-laurel_, _Stramonium_, &c. 5. NARCOTICO-ACRID, embracing such articles as produce the united effects of the two former, and which constitute some of the most deadly poisons, as the _Ticunas_, _Nux-vomica_, _Belladonna_, _Tobacco_, _Hemlock_, _Digitalis_, &c. 6. SEPTIC POISONS, _contagious miasmata_, _putrid exhalations from animal matter_, _Sulphuretted Hydrogen_, the _venom of the viper_, &c. The value of this classification has been very justly stated to consist in its combining to a certain degree, the advantages of a pathological arrangement with those of one founded on the basis of Natural History; for, while it is strictly pathological, it at the same time distributes the different poisons, with some few and unimportant exceptions, in an order corresponding with that of their natural history. The First two classes, for instance, present us with substances of a mineral origin; the Third and Fourth, with those which are chiefly of a vegetable nature; and the Sixth, with objects principally belonging to the animal kingdom. The importance of acknowledging a division, which has a reference to the organic and inorganic kingdoms of Nature, is considerable in a chemical point of view; for in enumerating the various experiments to be instituted for the detection of poisons, we are thus enabled to bring together a connected series of processes, nearly allied to, intimately connected with, and in some respects mutually dependent upon, each other. At the same time it must be acknowledged, that this classification has many defects and some fallacies. In the first place, it has little or no reference to the enlarged views of the modern physiologist, respecting the “_modus operandi_” of Poisons; nor indeed is its construction susceptible of such modifications and improvements, as can ever render its degree of perfection progressive with the advancement of science. In the next place, the classes are in many particulars ill defined, and indistinctly, if not erroneously, divided. How questionable, for instance, are the boundaries which separate