Poison. A poison is a substance which, when introduced into the body, is capable, by virtue of its own inherent chemical properties, of causing impairment of health or of destroying life. Poisons have been classed as irritants and neurotics, the latter group being sometimes subdivided into narcotics and narcotico-acrids. The principal irritant poisons are the mineral acids, oxalic acid, the alkalies, phosphorus, arsenic, antimony; certain salts of copper, mercury, and lead; savin, croton oil, colchicum, and cantharides. The chief symptoms produced by poisons of this kind are those of irritation of the alimentary tract, pain, nausea or actual vomiting, and purging are common, cramp in the limbs, and faintness or even extreme collapse may be present. Some of these poisons actually corrode the tissues subjected to their influence; this notably happens in the case of the mineral poisons. The chief neurotic poisons are opium, belladonna, alcohol, ether, chloroform, chloral, prussic acid, and strychnia. These poisons act mainly upon the nervous system. Certain gases when inhaled exercise poisonous properties. The chief of these are carbonic acid, which collects in mines, and in connection with the burning of lime; carbonic oxide, which is a constituent of coal-gas, is developed in charcoal-burning; and sulphuretted hydrogen.