Poisonous substances have been very differently arranged by different authors, each appearing to have adopted a classification best suited to promote the particular views and objects of his own pursuit; thus, the botanist and chemist, engaged in the examination of the physical characters by which poisons may be individually distinguished and identified, have very judiciously erected their system upon the basis of natural history. The pathologist, whose leading object is the investigation of the morbid effects which follow the administration of these agents, with equal propriety and justice prefers a classification deduced from a generalization of the symptoms they are found to occasion; while the physiologist, who seeks to ascertain through what organs, and by what mechanism they destroy life, may be reasonably expected to arrange the different poisons under divisions corresponding with the results of so interesting an inquiry.

To meet the comprehensive views of the forensic toxicologist, an arrangement would seem to be required, that should at once embrace the several objects which we have just enumerated; for the data from which the proof of poisoning is to be inferred, are, as we have often stated, highly complicated in their relations. No such classification, however, can be accomplished, and we are therefore compelled to select one which may approach the nearest to our imaginary fabric. That which was proposed by FodÉrÉ,^[210] and adopted, with some trivial alteration in the order of succession of the classes, by Orfila, in his celebrated system of toxicology, although it has many defects and some errors, nevertheless merits the preference of the forensic physician; its basis is strictly pathological, and yet it 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 principally of a vegetable nature; and the sixth, with objects chiefly belonging to the animal kingdom. The importance of acknowledging a division, which has a reference to the three great kingdoms of Nature, is perhaps greater than the reader may anticipate; for in enumerating the various experiments to be instituted for the detection of poisons, we are, by such an arrangement, enabled to bring together a connected series of processes, nearly allied to, intimately connected with, and in some respects, mutually dependant upon each other.

The following is the arrangement of FodÉrÉ as modified by Orfila: viz. Cl. I, Corrosive, or Escharotic poisons. Cl. II, Astringent poisons. Cl. III, Acrid or Rubefacient poisons. Cl. IV, Narcotic or Stupefying poisons. Cl. V, Narcotico-Acrid poisons. And Cl. VI, Septic or Putrefying poisons.

Class I. Corrosive or Escharotic Poisons. Such as corrode and burn the textures to which they are applied. When internally administered they give origin to the following symptoms: violent pain accompanied with a sense of heat and burning in the stomach, and throughout the whole extent of the alimentary canal; frequent vomitings, often sanguineous, and alternating with bloody diarrhoea, with or without tenesmus; the pulse hard, small, frequent, and at length imperceptible; an icy coldness of the body; cold sweats; a great anxiety and oppression at the prÆcordia; and hiccup. Sometimes the heat of the skin is intense, the thirst inextinguishable, and the unhappy patient is tormented with Dysuria and Ischuria, violent cramps in the extremities, and horrid convulsions, which are relieved only by death. Such are the general symptoms by which this species of poisoning is characterised; the rapidity with which the symptoms terminate their course, will depend upon the violence of the dose, and the particular species of poison which has produced them; there are, moreover, other symptoms which will be more conveniently described, when we come to speak of the effects of corrosive poisons individually. In this class are ranked the following substances. Metals. I. Arsenic—1. Arsenious Acid, or white oxide of Arsenic. 2. Arsenites, or combinations of that acid with salifiable bases. 3. Arsenic Acid. 4. Arseniates, or combination of the preceding acid with the bases. 5. Sulphurets of Arsenic, or Orpiment and Realgar. II. Mercury—1. Corrosive Sublimate of Mercury, or Oxy-muriate of Mercury. 2. Red Oxide of Mercury. 3. Red Precipitate, or Nitric Oxide of Mercury. 4. Other preparations of Mercury. III. Antimony—1. Tartarized Antimony, or Tartar Emetic. 2. Oxide of Antimony. 3. Antimonial Wine. 4. Muriate of Antimony, or Butter of Antimony. IV. Copper—1. Blue Vitriol, or Sulphate of Copper. 2. Verdegris. 3. Oxide of Copper. 4. Other preparations of Copper. V. Tin—1. Muriate of Tin. VI. Zinc—1. Sulphate of Zinc, or White Vitriol. 2. Oxide of Zinc. VII. Silver—1. Nitrate of Silver, or Lunar Caustic. The Concentrated Acids—1. Sulphuric. 2. Muriatic. 3. Nitric. 4. Phosphoric, &c. Hot Liquids—1. Boiling water. 2. Melted Lead. The Caustic Alkalies—1. Potass. 2. Soda. 3. Ammonia. The Caustic Alkaline Earths—1. Lime. 2. Baryta. 3. Muriate, and Carbonate of Baryta. Cantharides. Phosphorus.

Class II. Astringent Poisons. They occasion a remarkable and unrelenting constriction of the great intestines, especially the colon, so as to resist the operation of the most powerful cathartic remedies. Violent cholics ensue, and partial paralysis; in the end if the dose be sufficiently large, or if small doses have been frequently repeated, they will excite inflammation of the alimentary canal, but it is not succeeded by that disorganization which generally characterises the operation of poisons, belonging to the preceding division. We rank under the present class only the preparations of Lead, viz. 1, Acetate of Lead, or Sugar of Lead; 2, Oxides of Lead; Red Lead; Litharge; 3, Various Saturnine impregnations.

Class III. Acrid, or Rubefacient Poisons. These poisons are known by their producing an acrid taste, more or less pungent and bitter; a burning heat, and considerable dryness in the mouth and fauces; and a constriction, more or less painful, in the throat. Acute pains are, after a short interval, experienced in the stomach and bowels, which are quickly followed by copious vomiting and purging, and which continue, with the most painful efforts, long after the alimentary canal has been completely evacuated. A few hours after, phenomena are observed which indicate a lesion of the nervous system, such as vertigo, dilated pupils, dejection, insensibility, laborious respiration, and death. The lesions of texture, occasioned by the action of Acrid poisons, have the greatest analogy to those produced by Corrosive poisons; in fact, says M. Orfila, “we do not hesitate to declare, that there exists a perfect identity between the alterations of the digestive canal produced by the poisons of these two classes, when introduced into the stomach.” The substances included under this class belong, for the most part, to the vegetable kingdom, such as Scammony, Camboge, Black and White Hellebore, Bryony, Euphorbium, Seeds of the Ricinus, Iatropa Curcas (Indian nut), Croton Tiglium, Squill, Aconite, &c. &c.

Class IV. Narcotic, or Stupefying Poisons. Such as occasion stupor, drowsiness, paralysis, or apoplexy, and convulsions. They do not produce any change in the structure of parts to which they are applied. M. Orfila has satisfactorily ascertained that no alteration can be discovered, on dissection, in the digestive canal of persons who have swallowed any one of the poisonous substances of this class.

Class V. Narcotico-Acrid Poisons. This division, as its name implies, is intended to receive such substances as produce the united effects of those belonging to the two preceding classes, acting for instance at the same time, as narcotics and rubefacients. Amongst the articles of this class the following may be enumerated, Belladonna, Stramonium, Tobacco, Foxglove, Hemlock, Nux Vomica, Camphor, Cocculus Indicus, certain Mushrooms, Alcohol, &c. &c.

Class VI. Septic and Putrefying Poisons. By this term are included those poisons which, according to Orfila, “occasion a general debility, dissolution of the humours, and syncope, but which do not, in general, alter the intellectual faculties.” The articles of this class belong almost entirely to the animal kingdom, with the exception perhaps of a few gaseous compounds, and the Spurred Rye, or Ergot, viz. venomous animals; animals whose fluids have been depraved by antecedent disease; the poison of fishes; substances in a state of putridity; Spurred Rye, or Ergot.

Such is the classification which, for reasons already stated, it is our intention to adopt on the present occasion. We shall, however, in an additional chapter, under the title of “AËrial Poisons,” treat of those substances which are exclusively capable of acting upon the body through the medium of the atmosphere, or which require to be in a state of vapour, or gas, to ensure their operation.

With regard to the classification of FodÉrÉ and Orfila, we must here observe that we follow it only conventionally, and that, while we acknowledge it as being very convenient for the consideration of poisons, in reference to their forensic relations, yet we must not be considered as insensible to its many defects and 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 Corrosive from Acrid poisons? even the respective species of each class are, in many instances, less allied to each other than the great divisions to which they are subordinate. As an exemplification of this fact we have only to compare the physiological actions of Arsenic and Corrosive Sublimate; the former of these substances occasions death by being absorbed, and thus acting as a vital agent, the latter, by its local action as a caustic on the textures with which it comes in contact. In the same manner, if we examine the individual actions of the different species composing the class of “Acrid” poisons, we shall find the same want of uniformity; thus the Spurge-flax, and the Jatropa Curcas act by occasioning a local inflammation, while the Hellebore, being rapidly absorbed, exerts a fatal action on the nervous system, and produces only a very slight inflammation. The class of Narcotic poisons is more absolute in its definition, and more uniform in its physiological affinities, and therefore less objectionable, than the divisions to which we have just alluded; but the propriety of the term “Narcotico-Acrid” may be very reasonably questioned;^[211] even Orfila expresses his doubts upon the subject, “because the narcotic or sedative effects only follow the previous excitement.” Some of the poisons, under this last mentioned class, are rapidly absorbed, and act, through the medium of the circulation, on the nervous system, without producing any local inflammation; whilst others, again, merely act upon the extremities of the nerves, with which they come in contact, and without being absorbed, occasion death by a species of sympathetic action.

These few objections, and many more might be adduced, are sufficient to demonstrate the imperfection of the classification under consideration, and which would render it wholly unavailable to the pathologist who must adopt his treatment according to the physiological action of each poison. The author has accordingly, in his “Pharmacologia”^[212] ventured to propose an arrangement, in conformity with such views; and the following sketch of it may perhaps form a useful introduction to the general observations which it will be hereafter necessary to offer upon the “modus operandi” of poisons.