THE RESPIRATORY SYSTEM. 471 



The Pleura. 



HYDBOTHOBAX. 



Non -inflammatory accumulations of clear serum in the pleural cavi- 

 ties are of frequent occurrence. They occur under conditions similar 

 to those which lead to dropsy in other parts of the body lesions of the 

 heart, liver, and kidneys, and changes in the circulation and in the com- 

 position of the blood. 



.If the amount of serum be large it may compress the lower lobes of 

 the lungs. 



HYDBO-PNEUMOTHOBAX-PYO-PNETJMOTHOBAX. 



The presence of air in the pleural cavities is usually associated with 

 a serous or purulent exudate. It may occur as the result of perforation 

 of the lung, from rupture, from ulceration of tuberculous lesions at the 

 pleural surfaces, from injuries to the chest wall, perforation of the dia- 

 phragm by suppurative or cancerous lesions of the oesophagus, stomach, 

 or intestine, as well as in a variety of other conditions. Gas may form 

 in the pleural cavities in infection by the bacillus aerogeues capsulatus. 



HEMORRHAGE. 



Subpleural ecchymoses may occur in asphyxia or during infectious 

 diseases or intoxications. More extensive extravasations of blood 

 haematothorax may be the result of injuries to the wall of the thorax or 

 the rupture of aneurism. 



Haemorrhagic Exudates are usually associated with tuberculous inflam- 

 mation of the pleura or with infarctions of the lungs, carcinoma, or inju- 

 ries, infectious diseases, or cirrhosis of the liver. 



INFLAMMATION. (Pleuritis, Pleurisy.) 



Inflammation of the pleura may occur as an independent lesion, but 

 it is commonly associated with pathological processes in the lungs, peri- 

 cardium, abdomen, or chest wall. It may be exudative in character, 

 usually associated with more or less proliferation of the mesothelial 

 ("endothelial") and connective-tissue cells, or it may be productive 

 with the formation of new connective tissue. These phases of inflamma- 

 tion may be associated. Through the production of new connective tis- 

 sue, repair of the acute inflammatory lesion is commonly effected. In 

 the exudative forms of pleurisy the exudate may consist of fibrin, or of 

 serum and fibrin, or of serum with fibrin and pus. 



Simple Fibrinous Pleurisy (Dry Pleurisy ; Pleuritis Sicca). This may 

 involve circumscribed areas of the costal, mediastiual, diaphragmatic, 

 or pulmonary pleura, less frequently the entire pleura of one side of the 



