COUGH, in physiology, a deep inspiration of air, followed by a sudden, violent and sailor ous expiration, in a great measure involuntary, and excited by irritation of the air-passages, due to the presence of some foreign material or irritation of the nerves distributed to the respi ratory organs. The organs of respiration are so constructed that every foreign substance, ex cept atmospheric air, stimulates them. The smallest drop of water entering the windpipe is sufficient to produce a violent coughing, by which the organs labor to expel the irritating substance. A similar effect is produced by in haling smoke, dust, etc. The sudden expulsion of air from the lungs is produced by the violent contraction of the diaphragm and the muscles of the breast and ribs. The contraction of the muscles is due to impressions reaching them by their motor nerves, such impressions coming from the nerve-centre in the medulla, thrown into activity by stimuli received from the irri tated sensory nerves of the air-passages. The sensation of obstruction or irritation, which gives rise to cough, though sometimes perceived in the chest, especially near the pit of the stomach, is very often confined to the trachea, or windpipe, and especially to its aperture in the throat, termed the.giottis. Of the various irri tations which give rise to cough, some occur within the cavity of the chest; others are ex ternal to that cavity; some exist even in the viscera of the pelvis. Of those causes of cough which take place within the chest, the disorders of the lungs themselves are the most common, especially the inflammation of the mucous mem branes. Here the cough may be a dry one, that is, without expectoration, and this occurs in the early stage of the affection, or a loose cough attended by expectoration, as in the later stage. In the former case it is due to the dry inflamed mucous membrane being very irritable, so that the cough is excited even by the coldness of the inspired air. In the latter case the presence of the defluxion causes the cough and thus ex cites its expulsion.
Pleurisy, or inflammation of the serous mem brane which covers the lung and lines the interior of the chest, also gives rise to congk this disease being almost invariably accompanied by inflammation of the outer layer of the tissue of the lung. It may be simple, but is very fre quently associated with tuberculosis. Another common cause of cough which has its seat in the chest is inflammation of the lungs. In this disease there is inflammation of the tissue of the lungs, with exudation of fibrin, which solidifies the lungs and shuts up the air-cells. Much constitutional disturbance accompanies it: In the progress of the disease the exuded mate rial softens, and, being swept up the air-tubes, irritates the passages and brings on the cough by which it is expelled. In such a case the cough is desirable rather than the reverse, since it is nature's method of sweeping out the foreign substance from the air-cells and tubes. Another frequent origin of cough is the rupture of some of the blood vessels of the tangs, and the con sequent effusion of blood into the cells, which is expelled by the cough that its irritation excites, constituting what is technically termed htemop tysis, or spitting of blood. Cough is also excited by the existence of tubercles in the lungs, one of the most frequent causes of consumption; and by cancer and growths in the lungs.
Then the irritation may arise at the back part of the throat, no disorder being present in the windpipe, bronchial tubes or lungs. Thus a
long uvula, by tickling the back of the throat, may be the cause of a most persistent dry cough, coming on specially when the person lies down. Enlarged tonsils, a chronically thick condition of the mucous membrane of the back of the throat, small growths or polypi in this neighbor hood or in the box of the windpipe, may main tain a most troublesome cough. Direct irrita tion of the nerves connected with respiration, as by the pressure of a tumor, the pressure, for example, of an aneurism in the chest on one of the nerves of the larynx, may excite spas modic cough of a suffocative kind. Again, cough is very often excited by reflex irritation, the seat of the irritation being a long way from the air-passages. Where a cough is excited by disorders of parts external to the cavity of the chest, it is generally dry, as the irritating cause is external, and not any obstructing matter in the lungs themselves. Disorders of the viscera of the abdomen, especially of those which lie in contact with the diaphragm (the muscular curtain separating the cavities of the belly and chest), frequently induce a cough. A short, dry cough invariably attends inflammation of the liver, whether acute or chronic, and accom panies the various tubercular and other obstruc tions in that organ. Hence inflammation of the liver is not infrequently mistaken for inflam mation of the lungs; and in some of the chronic diseases of the liver the cough is occasionally complained of as the most urgent symptom. The presence of pain in the right side, shooting up to the top of the shoulder, the dryness of the cough, and pain, enlargement, hardness or uneasiness on pressure below the ribs of that side, will afford the best means of distinguishing whether a disease of the liver is the origin of the cough. Disorders of the stomach are also often accompanied with a cough of the same dry and teasing nature. A short cough is, therefore, a frequent symptom of indigestion. In short, there is scarcely any one of the viscera in the cavity of the abdomen the irritation of which, in a state of disease, has not excited cough. Disorders of the spleen, pancreas, and even the kidneys, have all given rise to this symptom; and external tumors attached to them have had the same effect. Any distension of the abdomen, which, by its pressure upward, impedes the descent of the diaphragm, and con sequently the expansion of the lungs, occasions cough. The variety of causes from which coughs may arise must convince every reader of the absurdity of attempting to cure all kinds of cough by the same remedy. The treatment can be satisfactorily indicated only when the real cause is ascertained. When a long uvula is the cause a small piece may be snipped off ; when it is a relaxed condition of throat, or a similar state of the box of the windpipe, local applica tions, paints directly applied by a brush, or inhalations, are the suitable remedies. One of the commonest coughs attends slight swelling and irritability about the larynx. To relieve this warm poultices should be applied to the front of the neck, or a piece of flannel sprinkled with turpentine should be placed over the larynx on the neck. In bronchitis and inflammation of the lungs the treatment of the cough resolves itself into the treatment of the special disease, and so with the cough due to diseases of distant organs. Often soothing remedies must be given to allay the excitability of the irritated nerves. Certain coughs are purely psychogenic in origin and are to be grouped with the psychoneuroses.