490 



THE RESPIRATORY SYSTEM. 



cells lining the air vesicles may be swollen, they sometimes proliferate, 

 and are usually detached in considerable numbers. Catarrhal bronchitis 



and pleuritis may at 

 this time develop. 

 This is called the 

 stage of " conges- 

 tion" or " engorge- 

 ment " and may last 

 for a few hours or 

 for several days. 



As the process 

 continues red blood 

 cells, but especially 

 polymorphonuclear 

 leucocytes, and 

 fibrin accumulate in 

 the air spaces and 

 smaller bronchi, so 

 that the portion of 

 lung involved be- 

 comes solid and fri- 

 able, somewhat re- 

 sembling the liver 



in color and consistency; hence the term "red hepatization" which has 

 been used to indicate this condition. The cut surface of the consoli- 

 dated portion is dry and coarsely granular, the granules being plugs or 

 casts of exudate in the air spaces. A light scraping of the cut sur- 



FIG. 270. ACUTE LOBAR PNEUMONIA EARLY STAGE. 

 This single air vesicle shows congestion of the capillaries in the walls, 

 and a small amount of exudates, fibrin, leucocytes, red blood cells, and ex- 

 foliated epithelium. 



FIG. 271. ACUTE LOBAR PNEUMONIA-STAGE OF " RED AND GRAY HEPATIZATION." 

 The air vesicles are filled with exudate consisting largely of leucocytes, fibrin, and serum with a few 



epithelial cells. 



face of the lung with the knife readily removes these granules or plugs 

 of exudate, which consist largely of fibrin and leucocytes with red blood 



