Carminatives are substances which aid the expulsion of gas from the stomach and intestines. They appear to do this by increasing the peristaltic movements of these organs, and in the case of the stomach by causing the lower end of the oesophagus or cardiac sphincter, and perhaps sometimes the pyloric sphincter, to dilate so as to allow of the exit of gas. The stomach naturally contains a certain amount of gas, chiefly nitrogen and carbonic acid. The nitrogen is derived from air which has been swallowed, the oxygen with which it was mixed being absorbed by the walls of the stomach.

For respiration goes on in the stomach, as well as in the lungs, though only to a slight extent in mammals, and oxygen is absorbed and carbonic acid excreted. The stomach, therefore, generally contains carbonic acid in addition to nitrogen; some of the carbonic acid also is derived from the food. In addition to these gases there is frequently hydrogen present: hydrogen and a quantity of carbonic acid being formed by processes of fermentation going on in the food. Sometimes instead of pure hydrogen marsh-gas is formed, which takes fire when expelled from the stomach, and not unfrequently the hydrogen unites with sulphur, forming sulphuretted hydrogen, causing to the patient an unpleasant taste of rotten eggs in the mouth, or giving their smell to the breath. It is probable that this last occurrence is due in many cases to the presence and decomposition in the stomach of bile, which contains sulphur as one of its constituents.

When digestion is rapid and complete, little or no fermentation occurs, very much less gas is formed, and therefore there is no uncomfortable distension.

There are several drugs which tend to prevent fermentation, while they hardly interfere at all with the action of the gastric juice. Among these may be mentioned creasote, sulphurous acid, and bitters, though the anti-fermentative action of the last has been denied. These substances may all be regarded as adjuvants to carminatives, and so indeed may pepsin, dilute alkalies, and all other remedies which stimulate the secretion of gastric juice and thus aid digestion.

Where there is any tendency to venous congestion in the stomach, there will be interference with the respiration in the stomach, and thus a greater tendency to the accumulation of gas. Any conditions interfering with the circulation, such as mitral disease or hepatic congestion, will thus tend to cause flatulence, and in such cases digitalis and cholagogues will prove useful adjuvants to carminatives.

It is possible that much mucus covering the surface of the stomach may interfere both with absorption and with gastric respiration. Charcoal has been given to remove flatulence, on the supposition that it absorbs the gases in the stomach. But it only absorbs gas when it is dry, and the beneficial action which it certainly possesses is probably a mechanical one in removing mucus and stimulating circulation. Possibly bismuth, nitrate and carbonate, and magnesium, oxide and carbonate, act similarly, though less powerfully.

The chief Carminatives belong to the classes of aromatic oils, alcohols, or ethers. They are: Allspice and oil. Anise and oil. Asafoetida. Cajeput oil. Capsicum. Caraway and oil. Cardamoms. Chilies. Chloroform.

Cinnamon and oil. Cloves and oil. Coriander and oil. Dill and oil. Ether and acetic ether. Fennel. Ginger. Horseradish.

Mace. Mustard. Nutmeg and oil. Pepper.

Peppermint and oil. Spearmint and oil. Spirits. Valerian and oil.

Uses. - Carminatives are employed (1) to remove pain and distension of stomach and intestines caused by flatulence; (2) to render peristaltic action regular, and diminish local spasm and pain depending upon it. They are useful both in cases where the spasm is due to irritation of the stomach and intestines by irritant articles of food, irritant secretions, or irritant medicines. They are therefore commonly used not only in griping and colic pains due to indigestion, worms, or exposure to cold, but as adjuvants to purgatives in order to lessen the griping pain, which they often cause when given alone. In addition to this, by rendering the peristaltic action of the bowel more regular, they assist the action of the purgatives.