Coughing, considered physiologically, consists (1) in a long inspiration which fills the lungs to a greater extent than usual; (2) in the closure of the glottis, or narrow opening in the organ of voice (see LARYNX), at the commencement of the act of expiration; and (3) in the sudden forcing open of the glottis by the violence of the expiratory movement. In this way, a blast of air is driven upwards from the lungs through the mouth, which carries with it any sources of irritation that may have been present in the air-passages. Coughing may occur from irritation in the back of the throat, in the larynx, trachea, or bronchial tubes, and may be excited by acrid vapours, by irritant gases, or by articles of food or drink—such as even a drop of water or a crumb of bread—making their way into the air-passages instead of into the pharynx, or by excessive or morbid secretion from the walls of the air-tubes, or even by the entrance of cold air, when the lining membrane of the air-passages is abnormally irritable. More rarely it results from irritation of other parts, as the ear, and possibly the stomach.
The object of coughing in the animal economy is unquestionably to guard against the danger of the entrance of mechanical and chemical irritants into the air-passages; and accordingly the mucous membrane, especially of their upper part, is endowed with a most exquisite sensibility which, when aroused by irritation or by a state of disease, provokes incessant coughing until the irritation be allayed or removed. Cough is an exceedingly common symptom of all diseases of the respiratory organs. The treatment of coughing must first be directed to the removal, if possible, of the cause which excites it. But besides, when once begun, coughing frequently becomes excessive, and so irritating or exhausting to the patient, from too great sensitiveness of the nervous mechanism which produces it; and this tendency, when injurious, must also be combated. The remedies suitable to most cases of cough are therefore Expectorants (q.v.) and nervine sedatives, especially opium, morphia, and hydrocyanic acid; 'cough mixtures' generally contain both. Such household remedies as liquorice, jujubes, black-currant jelly, or linseed tea are often of service. See also under names of diseases in which cough occurs.
Cough occurs amongst the lower animals under similar conditions. From continued breathing of a close foul atmosphere, the bronchial mucous membrane becomes unduly irritable, hence the prevalence of chronic cough amongst the cows in our overcrowded town-dairies. Chronic cough also occurs in horses, usually as a sequel to an attack of cold. It constitutes unsoundness, is best treated by repeated doses of belladonna and camphor, but often requires for its entire removal a run at grass.
Cough is an accompaniment of teething, and is also common in diseases of the digestive organs. See PNEUMONIA, CONSUMPTION, BRONCHITIS, CATARRH, &c.