THE MICROSCOPE IN PATHOLOGY. 259 



Croupous pneumonia is generally an independent affec- 

 tion, while the catarrhal and interstitial forms of inflam- 

 mation of the lungs usually result from preceding bron- 

 chial or pulmonary lesion. The first stage is that of 

 engorgement, in which the capillaries dilate and coil so 

 as greatly to diminish the air capacity of the alveoli. In 

 the second stage, that of red hepatization (Fig. 211), the 



FIG. 211. 



Kecent croupous pneumonia, a. Alveolar septa with injected capillary vessels. 6. The 

 exudation. 1-300. After RIXDFLEISCH. 



exuded contents of the capillaries of the air-cells, red and 

 white corpuscles, and serum, are coagulated by the fibrin 

 into a solid body. The third stage is that of yellow or 

 gray hepatization, characterized by a greater proportion 

 of white blood-cells and their progeny, mingled with the 

 results of commencing fatty metamorphosis. Purulent 

 infiltration, or resolution, is sometimes called the fourth 

 stage of this disease. Here the fibrin melts down to a 

 soft amorphous gelatin, and the young cells undergo fatty 

 degeneration. Granular pigment also is mixed w T ith the 



