POISONS. A poison is commonly defined to be a Substance which, when adminis tered in small quantity, is capable of acting deleteriously on the body; but this definition is obviously too restricted, for it would exclude numerous substances which are only poisonous when administered in large doses, as niter, and the salts of lead, antimony, etc. A person may be as effectually poisoned by an ounce of niter as by five grains of arsenic, and hence the quantity required to kill must not enter into the definition. Dr. Taylor suggests the following as the most comprehensive definition that can be given: "A poison is a substance which, when taken internally, is capable of destroying life without acting medicinally on the system;" but this definition is not perfect, for it does not include poisons that act by absorption when applied to a thin and delicate membrane, as glanders, syphilitic poison, etc., or those which must be introduced directly into the circulation by a puncture or abraded surface, as the poison of insects. scorpions, and serpents, the wourali poison, and that of animals suffering from hydrophobia. Omit ting, for the present, the consideration of the cases not included in Dr. Taylor's proposed definition, we may consider poisons as divisible into three classes, according to their mode of action on the sygtem—viz., irritants, narcotics and narcotico-irritants.
The irritants, when taken in ordinary closes, speedily occasion intense vomiting and purging, and severe abdominal pain. They act chiefly on the stomach and intestines, which they irritate, inflame, and frequently corrode, and may thus occasion ulceration, perforation, or gangrene. Among those which possess corrosive properties, are the strong mineral acids, caustic alkalies, corrosive sublimate, etc. ; while among the pure irritants which exert no destructive chemical action on the tissues with which they come in contact. may be mentioned arsenic, cantharides, carbonate of lead, etc. The narcotics act specially on the brain and spinal cord. Among their most common symptoms are
giddiness, headache, obscurity of sight or double vision, stupor, loss of. power of the voluntary muscles, convulsions, and, finally, complete coma. Moreover, many of the narcotic poisons present special symptoms, in some cases strongly resembling pure special diseases. Thus there is an almost exact similarity in the symptoms of poisoning by opium and of apoplexy, while prussic acid and some other poisons give rise to symptoms closely resembling thoSe of epilepsy. These poisons have no acrid, burning taste, nor do they usually give rise to vomiting or diarrhea, and, excepting a slight fullness of the cerebral vessels, they leave no well-marked post 9norteni appearance. They are few in number, and none of them belong to the mineral kingdom. The narcotico-irritants have, as their mune implies, a mixed action. "At variable periods," says Dr. Taylor, "after they have been swallowed, they give rise to vomiting and purging, like irritants, and soon or later produce stupor, coma, paralysis, and convulsions, owing to their effect on the brain and spinal marrow. They possess the property, like irritants, of irritating and inflaming the alimentary canal. As familiar examples, we may point to aux vomica, monkshood, and poisonous mushrooms The fact of the symptoms occurring. after a meal at which sonic suspicious vegetables may have been eaten, coupled with the nature of the symptoms themselves, will commonly indicate the class to which the poison belongs. Some narcotico-irritants have a hot, acrid, taste, such as the aconite or monkshood; others an intensely bitter taste, as nux vomica and its alkaloid strychnia." For a notice of the most important rules to be observed by the physician in all cases of suspected poisioning, both with respect to the symptoms and to the inspection of the body, we must refer to any of the standard works on poisoning, or on medical jurisprudence.