CHRONIC INTERSTITIAL PNEUMONIA. 345 



cells and migrated leukocytes. The air-spaces immediately 

 surrounding the bronchus are filled with a fibrillary network 

 of fibrin, a variable number of red and white blood-corpus- 

 cles, and epithelial cells. A little further from the bronchus 

 the air-spaces contain only the large, flat, rounded or oval cells 

 derived from the proliferating epithelium which lines the 

 alveolus. 



In the later stage of gray spleiiization there are fatty degene- 

 ration and liquefaction of the alveolar exudate, part of which 

 is finally expectorated and part absorbed by the lymphatics. 



Resolution is the usual termination. With the absorption 

 of the alveolar exudate the round-celled infiltration of the 

 walls disappears ; the whole process takes much longer, how- 

 ever, than in lobar pneumonia. 



CHRONIC INTERSTITIAL PNEUMONIA. 



Chronic interstitial pneumonia, or fibrosis, is characterized by 

 an excessive formation of new fibrous tissue, involving the 

 alveolar walls and the supporting connective-tissue frame- 

 work of the lungs. It may be secondary to lobar or lobular 

 pneumonia, or due to the inhalation of solid irritating patches 

 pneumokoniosis. 



The affected lung is generally smaller than normal, and 

 feels firm, fibrous, and elastic ; bronchiectatic cavities are fre- 

 quently met. When due to the inhalation of particles of coal 

 or carbon anthracosis the lungs are deeply pigmented ; 

 similar lesions occur in artificers in iron and steel siderosis 

 only the coloration is brown instead of black ; silicosis is the 

 term applied to an analogous condition in quarry men, in 

 which the lungs have a marble-like or slate-like appearance, 

 produced by inhalation of the dust-particles of dry silicious 

 stone. 



Microscopically there is noted thickening of the pleura, 

 the interlobular septa continuous with its deeper layer, the 

 peribronchial and peri vascular tissue, and the interalveolar 

 septa. The air-vesicles are compressed, their walls thickened 

 and fibrous (Fig. 153). Following lobar pneumonia, cases 

 have been described in which, in addition to the thickening 

 of the walls of the air-spaces, there was organization of the 



