Emetics, medicines used to produce vomiting. They may be divided into two classes, specific and irritant. The first class require for their operation absorption into the circulation, and they produce their specific effects whether they are absorbed from the stomach or injected directly into the blood. When taken internally their action does not commonly commence until after 20 or 30 minutes; then nausea, chilliness, and a feeling of weakness are produced, while the pulse is slow and soft; and as vomiting is induced, these give way to a flushed countenance, a warm skin, and a full pulse. The most important of these are tartar emetic (tartrate of antimony), potassa, ipecacuanha, and the lately discovered apomorphia, which is an artificial alkaloid, prepared, as its name indicates, from morphia. Tartar emetic has recently been supposed to produce its effect, like the second class, by an irritant action upon the mucous membrane of the stomach, to which it is either directly applied or by which it is excreted when injected into the blood. Apomorphia, when injected sub-cutaneously, acts with great rapidity and in much smaller dose than when given by the stomach.
Lobelia inflata, or Indian tobacco, has been largely used as an emetic by botanic practitioners, but is exceedingly depressing in its effects. Irritant emetics, as sulphate of zinc, copper, mustard, etc, on the other hand, produce vomiting by their direct effect upon the lining membrane of the stomach. Their action is immediate and unpreceded by any nausea or other precursory symptoms. They are used chiefly in cases of narcotic poisoning, and of accumulation in the bronchial tubes, where from the feebleness of the patient it is desirable to shun the depression preceding the action of ordinary emetics, while full and prompt vomiting is required. Emetics were formerly used extensively in the treatment of a large variety of diseases; but the careful observation of recent times has greatly restricted their employment. They find their most appropriate use in relieving the stomach from an excess of food, or from indigestible food, and from poisons, and occasionally in the treatment of bronchitis and croup.