2. _Remote Action._--This may be of reflex character, as seen in the shock produced by the pain caused by corrosive poisons, or the poison may exert a special action on certain structures, as belladonna on the cells of the brain, strychnine on the motor nerve cells of the spinal cord. 3. _In Both Ways._--Certain poisons, as carbolic or oxalic acids, act in this way. Age, idiosyncrasy, tolerance, and disease, all exert modifying influences on the action of a poison. The form in which the poison is swallowed and the quantity also determine its action. In the gaseous form, poisons act most rapidly and fatally. When in solution and injected hypodermically, they also act very rapidly. In the solid form they act as a rule slowly, and may even set up vomiting, and so may be entirely ejected by vomiting. Poisons act most energetically when the stomach is empty. If taken when the stomach already contains food, solution and absorption may be greatly delayed. Some poisons are cumulative in their action, and thus, even if infinitesimal doses be swallowed each day, there is a certain amount of storage in the tissues (though a certain percentage of the poison is being constantly eliminated), and at last symptoms of poisoning show themselves. =Classification of Poisons.=--As an aid to memory, the following classification is perhaps the best: I. _Inorganic._ 1. Corrosive acids and alkalies, and caustic salts (carbolic and oxalic acids also). 2. Irritant--practically all the metals and the metalloids (I. Cl. Br. P.). II. _Organic._ { Animal--venomous bites, food poisoning, cantharides. 1. Irritant { Vegetable--all strong purgatives, hellebores, savin, { yew, ergot, hemlock, laburnum, bryony, etc. 2. Neuronic. (a) Somniferous--opium and its alkaloids. (b) Deliriant--belladonna, hyoscyamus, stramonium, cannabis, cocaine, cocculus, camphor, fungi. (c) Inebriants--alcohol, ether, chloral, carbolic acid (weak), benzol, aniline, nitro-glycerine. 3. Sedative or depressant. (a) Neural--conium, lobelia, tobacco, physostigma. (b) Cerebral--hydrocyanic acid. (c) Cardiac--aconite, digitalis, colchicum, veratrum. 4. Excito-motory or convulsives--nux vomica, strychnine. 5. Vulnerants--powdered glass. III. _Asphyxiants._ Poisonous and irrespirable gases. IV.--EVIDENCE OF POISONING It may be inferred that poison has been taken from consideration of the following factors: Symptoms and post-mortem appearances, experiments on animals, chemical analysis, and the conduct of suspected persons. 1. _Symptoms_ in poisoning usually come on suddenly, when the patient is in good health, and soon after taking a meal, drink, or medicine. Many diseases, however, come on suddenly, and in cases of slow poisoning the invasion of the symptoms may be gradual.