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It also deserves notice, that a poison acts with different degrees of force and celerity in different parts of the same tissue; its absorption, for instance, would appear to be energetic in proportion to the number of veins,[218] although several apparent exceptions to this law might be adduced, and it is evident that the plethoric state of the part with respect to its blood-vessels has a considerable share in modifying the effects; this observation, however, has no relation to those poisons which operate on the system through the sympathetic communication of the nerves; Mr. Brodie, for instance, found that the poison of bitter almonds acted more speedily when applied to the tongue than when injected into the intestine, though the latter presents a much better absorbing surface.
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.