Emetics are medicinal substances which excite vomiting, their action being independent of any effect arising from the quantity of the agent introduced into the stomach.

While the action of an emetic is local as regards the stomach, it extends to almost every organ of the body, and in order that a substance of this kind shall produce its effect upon the stomach, it must first make an impression upon the cerebro-spinal axis. Within fifteen or twenty minutes after an emetic is administered there is experienced a feeling of distress, relaxation and faintness, with a cool, moist skin and small, feeble and irregular pulse, such symptoms increasing until emesis occurs; during which the face becomes flushed, the pulse full and frequent, with an increase in the temperature of the body. When the action of vomiting is over, the skin again becomes moist, the pulse soft and feeble, and a languid and drowsy feeling is experienced. Whatever may be the apparent necessity for evacuating the stomach, all the circumstances of the case must be considered, and, especially if there be much arterial excitement, with determination to the head, blood-letting should sometimes be premised.

When the full dose of an emetic is requisite, as in cases of poisoning, the object is to evacuate the contents of the stomach as speedily as possible; but in other cases it is better to administer the emetic substance in divided doses, frequently repeated, until the desired effect is produced.

In cases of torpor or congestion, it is sometimes necessary to arouse the system by retching or vomiting, which may be done by administering the emetic with only a small quantity of fluid ; but when the object is to empty the stomach, and duodenum merely, free draughts of tepid water or weak chamomile tea may be given as soon as nausea occurs. When the excitability of the stomach is greatly diminished by a narcotic, as in cases of poisoning, it is necessary to assist the emetic by the addition of some excitant. Vinegar, mustard or ammonia answer as excitants, when such an effect is caused by opium; but the stomach-tube is the best resource.

There are some few cases where emetics cannot be employed with safety, as in congestion of the brain, a great determination of blood to the head dependent upon constitutional causes, pregnancy, hernia, active hemorrhage from the lungs and uterus, acute gastritis, etc., etc.; and if emetics are allowable in such diseases or conditions, it is in nauseating doses only. When they are used merely to excite nausea, they are termed nauseants.

Emetics, by frequent use, are prone to cause an increased susceptibility of the stomach to their action; hence, persons of delicate habits should use them cautiously.

Therapeutically, emetics are employed to evacuate the stomach in cases of poisoning, undigested food, etc., to expel foreign substances from the throat or oesophagus; to excite nausea, in order to depress the vascular and muscular systems; to relieve spasm; to promote secretion and excretion, and to make decided impressions in the forming stages of certain fevers and delirium tremens.

To relieve excessive vomiting, resulting from the use of emetics, ice broken in small pieces and swallowed; lime water and milk (a teaspoonful of each, mixed cold and given at intervals of 15 or 20 minutes); a drop of creasote in a wineglass of water (a tablespoonful given every 15 or 20 minutes); 1/2 drop of diluted hydrocvanic acid in syrup and water, or in syrup of wild cherry bark (given every 15 minutes); or infusion of camphor (made with boiling water and given cold, a teaspoonful frequently repeated); brandy and water; clove or green tea; an anodyne injection; counter-irritant to the stomach (as a mustard plaster, a hot fomentation of brandy and clove or spice plaster).

Among the class of vegetable emetics are ipecacuanha, san-guinaria, mustard, lobelia, tobacco, squill; and mineral emetics, such as sulphate of zinc, sulphate of copper, tartar emetic, alum, common salt, turpeth mineral.