486 THE RESPIRATORY SYSTEM. 



region. On the other hand, if prolonged, fibrous tissue may form and 

 the involved portion may be finally converted into a cicatricial mass, 

 sometimes containing bronchiectatic cavities. 



EMPHYSEMA. 



Vesicular Emphysema. In forcible inspiration or expiration through 

 obstruction of the air passages, in coughing, or in the use of wind instru- 

 ments, or with consolidation or compression of portions of the lungs, the 

 walls of the air spaces of the lungs may be more or less distended, either 

 in circumscribed regions or over large areas of the lungs. This may de- 



FIG. 268. VESICULAR EMPHYSEMA. 

 Showing enlargement of the air spaces and thinning of their walls. 



velop in a short time, and then the condition is designated acute emphy- 

 sema. 



If the conditions which induce emphysema be persistent, as in chronic 

 bronchitis with difficult respiration and coughing, atrophy of the walls 

 of the air vesicles and alveolar passages may take place chronic emphy- 

 sema. The walls become thinner and are often perforated; adjacent air- 

 spaces coalesce, so that larger and smaller irregular, thin-walled cavities 

 are formed (Fig. 268). Destruction of the capillary network of the 

 atrophied walls occurs, and the lung may thus become pale and anaemic. 

 As a rule, the distention of the air spaces is most marked along the an- 

 terior margins of the lungs, but it may be more general. Through the 

 atrophy of the elastic tissue of the lungs, when the lesion is general and 

 advanced, these organs do not collapse w r hen the chest is opened. They 

 appear pale, are dry and soft, and pit on pressure by the finger. 



The microscopic picture is that of varying degrees of atrophy ; des- 

 quamatiou and fatty degeneration of the vesical epithelium are common. 



