PLEURAL CAVITY, DISEASES OF.—In addition to diseases of inflammatory origin, a number of other affections may occur in the thoracic cavity. In general dropsy, especially when due to heart or kidney disease, fluid collects also in this cavity, usually on both sides. Effusions of blood are most frequently the result of injury ; in rarer instances they are due to the rupture of an ANEURISM. This condition must be carefully distinguished from the hemorrhagic forms of pleurisy, which are almost invariably due to the presence of a tuberculous process. Accumulations of air and gas in the thoracic cavity are due either to the entrance of air from without through an injury to the chest-wall, or to the rupture of a pulmonary abscess which permits air to enter from the lung. The latter condition, in which, also, pus finds its way into the cavity, is usually connected with some tuber culous process, less often with pulmonary gangrene. The presence of air in the chest-cavity always produces considerable embarrassment of respiration, and is a most unfavourable complication, especially when considered in connection with the severe character of the original disease. Neoplasms, or tumours, in the pleural cavity are comparatively rare. They are either derived from the lung or from bits of tumours which have been transported thither by the circulation. This refers chiefly to cancer nodules.
of the pleura, the serous membrane investing the lungs. This is one of the most frequent of human ailments, hut rarely exists as a disease of itself, resulting in these rare instances from an injury to the thorax, or from a cold. As a rule, pleurisy is the immediate consequence of inflammatory processes in the neighbouring organs, such as pneumonia, pulmonary gangrene, tuberculosis of the lungs, or of the lymphatic glands situated at the root of the lungs, and inflammation of the endocardium or of the peritoneum. It may develop also from pathogenic agencies which reach the pleura through the circulation, in such diseases as blood-poisoning, purulent inflammations of joints, gout, or kidney troubles.
There are two varieties of pleurisy, the dry and the moist. The disease invariably begins \ vith a congestion in the blood-vessels of the pleura. This is followed by the exudation of fibrine, which is deposited on the pleura in the form of fine bands or as thick, irregular masses, often resulting in adhesions between that part of the pleura which covers the lung and that which is reflected over the ribs. This constitutes dry pleurisy. In addition to the
deposit of fibrine, there may be a copious exudation of blood-serum into the pleural cavity. Sooner or later this fluid may become purulent, and, in rare cases, there may be present in the pleural cavity an admixture of blood, or pure blood, constituting the moist form of the disease.
The onset of pleurisy may be marked by a sudden chill ; but in most instances the disease develops very gradually. The patient usually complains of a pain in the side, which is rendered worse by movements of the body, by yawning, coughing, or other exertions. To this is added shortness of breath, and a constant desire to cough. The patients lose their colour, they feel fatigued, and the appetite is diminished. The severer cases of pleurisy are accompanied by fever, but this rarely reaches a high point. If effusion into the pleural cavity occurs, the urine becomes dark in colour, lessened in amount, and contains a sediment. As the exudation is absorbed, the amount of urine again increases, and may be as much as 2 to 3 quarts daily.
There remain to he considered very briefly sonic of the distinguishing characteristics of the various forms of pleurisy. The ordinary mild cases of dry pleurisy run their course without causing much disturbance or pro ducing any marked symptoms. Even where exudation is present, robust persons may go about their business for several \reeks ; and only when the symptoms become increasingly distressing do they take to their beds. When an abundance of fluid is presence in the pleural cavity, the lung gradually becomes converted into a flattened, almost airless mass of tissue, which is pressed against the vertebral column. The heart is displaced to one side ; and the liver, stomach, and large intestine are pressed downward. In favourable cases the fluid is entirely absorbed, and a complete cure results. In severe cases the pleura is thickened, and the chest-wall may be drawn in as the result of starry contractions of the pleural membrane (see Plate XVII., Fig. 4).