THE RESPIRATORY SYSTEM. 



491 



cells and exfoliated epithelium (Fig. 271). The relative amount of 

 leucocytes, red blood cells, and fibrin in the air spaces varies greatly, 

 sometimes one, sometimes the other, preponderating (Fig. 272). The 

 fibrin fibrils often coalesce or swell, forming homogeneous, irregular 

 masses. On staining, large numbers of pneumococci may be found min- 

 gled with the other elements. While the general appearance of the lung 



*i% 



FIG. 272. ACUTE LOBAR PNEUMONIA. 

 Showing flbrinous exudale stained by Weigert's method. 



in this stage is red, it is often mottled with gray and frequently is not 

 uniformly solid. Although the capillary blood-vessels are compressed, 

 they for the most part remain pervious; but thrombosis is not infre- 

 quent. Fibrinous pleuritis is commonly present and the interstitial tis- 

 sue of the lung, while usually free from exudate, may be osdematous and 

 contain a few leucocytes and some fibrin. 



The quantity of exudate in the lung is often very large. Hodenpyl 

 has found it sometimes to be from three to four or even six pounds in 

 weight. 



In the usual course of events the red blood cells now lose their haemo- 

 globin, the exudate begins to soften, and the lung assumes a grayish 

 color gray hepatization or commencing resolution. The leucocytes and 

 exfoliated epithelium undergo granular and fatty degeneration ' or necro- 

 sis, and these with the fibrin soften and disintegrate (Fig. 273). The cut 



1 See on fatty degefieration of pneumonic exudates, Christian, Jour. Med. Re- 

 search, vol. x., p. 109, bibliography. 



