320 CLINICAL APPLIED ANATOMY. 



pulmonary artery, and leads to hypertrophy and dilatation of 

 the right cavities of the heart, with signs of back pressure in the 

 venous system. 



Compensatory emphysema, as its name denotes, is a form of 

 emphysema which occurs when for some other reason part of 

 the pulmonary tissue becomes functionless. The whole of the 

 opposite lung may become emphysematous when one lung is 

 crippled, and under such circumstances the mobility of the 

 mediastinum allows the active and over-distended lung to encroach 

 considerably on its fellow. Similarly when one lobe of a lung 

 becomes collapsed the remaining lobe or lobes of the same side 

 may become emphysematous, and when part of a lobe is airless 

 or cicatrised the pulmonary tissue immediately adjacent becomes 

 over-inflated. 



PLEURA AND MEDIASTINA. 

 PLEURAL INFLAMMATIONS AND EFFUSIONS. 



Effusions into the pleura may be passive and non-inflammatory, 

 or inflammatory. 



Passive effusions occur in connexion with heart failure, the 

 fluid poured into the sac accumulating there instead of being 

 constantly absorbed by the lymphatics. Karely a chylous effusion 

 is found, the thoracic duct rupturing into the sac in consequence 

 of injury or obstruction. In the posterior mediastinum the 

 thoracic duct lies close to the right pleural cavity, whilst in 

 the superior mediastinum and the root of the neck it is close 

 to the left one. 



Inflammatory effusions are frequent, and may be either serous 

 or purulent. When pleurisy complicates a specific fever, such as 

 rheumatism or scarlet fever, it is assumed that the infection is 

 carried to the pleura by the blood stream. There are many 

 systemic capillaries adjacent to the pleura. A uniform layer of 

 capillary blood-vessels lies on the surface of the lung, beneath 

 the visceral pleura, and is derived from the bronchial arteries. 

 Another wide-meshed plexus lies in the subpleural connective 



