A Violent Expiratory Movement - Cough, excited by some stimulus in the respiratory organs, in which the air is forcibly expelled, carrying with it the mucus or other products accumulated in the air passages. Any irritation from acrid vapors, liquid or solid foreign bodies, too abundant or morbid secretions, or even the action of cold air on the irritated mucous membrane, may produce a cough; the impression is conveyed to the respiratory nervous centre, the medulla oblongata, by the excitor fibres of the par vagum, and the motor impulse is transmitted to the abdominal and other muscles concerned in respiration. Coughing occurs when the source of irritation is in or below the posterior fauces, and sneezing when the irritating cause acts on the nasal mucous membrane. The act of coughing, as defined by physiologists, consists in a long inspiration which fills the lungs, the closure of the glottis when the expiratory effort commences, and the bursting open of the closed glottis by the sudden blast of air forced up from the air passages. The cause of cough may be in the respiratory system, or it may be symptomatic of disease in the digestive and other organs.

The cough in laryngitis, croup, and folliculitis arises from irritation in the throat and larynx; in bronchitis, pneumonia, pleurisy, and phthisis, the cause is in the thoracic cavity. Cough may be dry, as in the first stage of pleurisy, or humid, as in certain stages of pneumonia and in advanced consumption; the act may be single and with distant intervals, or paroxysmal and long continued, as in whooping cough, phthisis, and bronchial catarrh; it may be accompanied by a ringing metallic sound, as in croup and whooping cough, by a hollow resonance or gurgling, as in phthisis with cavities, or by hoarseness, as in laryngeal disease. The character of the cough is characteristic of certain diseases: that of whooping cough and of croup is highly diagnostic; in pleurisy it is dry and hard; in pneumonia, generally humid, with viscid rusty sputa; in consumption it varies with the stage of the affection; but in all these, taken in connection with other symptoms, the cough is a valuable diagnostic sign. Many rales, characteristic of morbid changes, are only or best recognized in the increased respiration after coughing. Cough is frequently accompanied by pain, as in acute pleurisy, pneumonia, and bronchitis; at other times painless, but exhausting, as in the paroxysms of spasmodic coughs.

Cough, symptomatic of other than pulmonary disease, is not accompanied by any characteristic phenomena discoverable by auscultation and percussion. The gravity of cough as a symptom depends on the disease in which it occurs; spasmodic coughs generally are not dangerous, except from the liability to rupture of vessels, or other simply mechanical consequences. For the relief of cough the prescriptions are almost innumerable, consisting of compounds of narcotics, antispasmodics, demulcents, expectorants, and alteratives, according to the character of the symptom, the stage of the disease, and the fancy of the attending physician.