Emetics are agents which produce vomiting or emesis.

Emesis is, in short, an antiperistaltic action, complex in its mechanism. Emetics are largely out of fashion in medicine at the present time, but are in so much demand when needed, particularly in poisoning, that their consideration is worthy of separate treatment.

The local or gastric emetics 1 are:

*Alum;

*Copper sulphate;

*Zinc sulphate;

* Yellow mercuric sulphate;

*Sodium chloride;

*Ammonium carbonate;

* Mustard.

Apomorphine hydrochloride, antimony and potassium tartrate, ipecacuanha, and lobelia are thought to be medullary emetics.

Local or gastric emetics are the more rapid in their action, producing emesis in from two to five minutes. The systemic emetics must be absorbed and pass to the medulla before they produce vomiting, consequently requiring more time to exert their influence. Moreover, the action of the latter class of emetics is of much longer duration and followed by greater depression of the muscular and circulatory systems, together with greater constitutional disturbance.

Some emetics act both locally and centrally. Tartar emetic and ipecacuanha affect the stomach locally, and it has recently been called in question whether their medullary action is even present, not to say important. Zinc sulphate and copper sulphate, while to a slight extent acting on the medulla, are classed as local emetics, because their principal action is upon the mucous membrane of the stomach.

Within a few minutes after an emetic has been ingested there is a feeling of nausea and distress, with decided muscular relaxation. The circulatory system is depressed; the pulse is small and irregular, and a sensation of faintness ensues. The flow of saliva is increased, and vomiting soon follows. During emesis the arterial tension is raised, the face is flushed, and there is an increase in bodily heat. When vomiting has subsided there is a reduction of temperature, with cardiac and muscular weakness, the skin being bathed in perspiration. Occasionally fatal syncope has followed the use of emetics.

1 (The drugs marked with an asterisk (*) are considered elsewhere in the present work.)

Antagonists. - Drugs known as Antiemetics are used to allay nausea and check vomiting. Like emetics, these agents are divided into Local Antiemetics or Gastric Sedatives and Direct or Systemic Antiemetics, according to their action.

Among the most important Antiemetics are the following:

Local Antiemetics or Gastric Sedatives.

(All of these are discussed elsewhere in the present work.)

Alcohol (especially champagne); Arsenic (small doses); Belladonna; Bismuth subnitrate and subcarbonate; Carbolic acid; Cerium oxalate; Chloroform; Cocaine; Creasote; Calomel (small doses);

Ether;

Ipecac (small doses);

Ice;

Opium;

Hydrocyanic acid;

Menthol;

Potassium nitrate;

Silver nitrate;

Sulphocarbolates;

Tincture of iodine (small doses).

Direct or Systemic Antiemetics or Gastric Sedatives.

Alcohol; Ammonium; Amyl nitrite Bromides;

Chloral;

Hydrocyanic acid; Nitroglycerin; Opium.

It will be observed that some drugs are both local and direct antiemetics.

There are certain measures which may be adopted to allay nausea and relieve vomiting, such as a recumbent posture and injection of large quantities of aerated water into the rectum.

Synergists. - The emetics are, of course, mutually synergistic. Emetics are adjuncts to antiperiodics and expectorants, although the latter do not particularly enhance the action of the former.

Emetic are used:

1. To empty the stomach in cases where the presence of undigested food occasions pain, headache, etc., or to expel some poisonous substance from the stomach. For this purpose the local emetics are preferable.

In cases of poisoning the local emetics are the more reliable.

2. To remove foreign bodies from the esophagus. For this purpose the direct or systemic emetics should be used.

3. To remove foreign bodies from the larynx, as in cases of membranous croup, laryngeal diphtheria, etc., the effort of vomiting being sometimes sufficient to dislodge and remove the membrane or other foreign substance.

4. To remove' the bronchial secretion in cases of bronchitis and catarrhal pneumonia. In these cases the direct emetics should be employed, preferably ipecacuanha or apomorphine, because they possess more expectorant properties.

5. To empty the gall-bladder in cases of biliousness or malaria, or where small gall-stones are present in the gall-duct, the compression of the liver between the diaphragm and the abdominal muscles expelling the bile from the liver into the duodenum and forcing the gall-stones through the duct.

6. To relax spasm of the pharyngeal muscles in cases of spasmodic laryngitis. For this purpose the systemic emetics are preferable.

Contraindications. - Emetics should not be given to persons suffering from aneurism, hernia, peritonitis, prolapse of the uterus or rectum, atheroma, or where there is very high arterial tension, a tendency to hemorrhage from the lungs or uterus, or a tendency to abortion.

The emetic drugs which have not been elsewhere discussed in the present work are here given in detail.