720 THE EESPIEATOEY TRACT. 



cles. In the initial stages of croupous pneumonia, or in its 

 milder forms, the so-called flabby hepa-tization, the pathologi- 

 cal changes are best observed. See Fig. 321.) 



Red hepatization, under the microscope, is characterized in 

 addition to the engorgement of the blood-vessels by the presence 

 of numerous red blood-corpuscles in the exudation plug, which is 

 found to consist of a varying amount of coagulated fibrine 

 closely attached to the wall of the alveolus. In the progress of 

 pneumonia a great many capillaries are destroyed, for the nearer 

 the process approaches to gray hepatization, the fewer are the 



FIG. 321. CROUPOUS PNEUMONIA. BLOOD-VESSELS INJECTED. 



W, wall of alveolus ; with the coagulated felt-work of fibrine filling the alveoli are entan- 

 gled K, red blood-corpuscles ; C, inflammatory corpuscles (emigrated, colorless blood-corpus- 

 cles?) ; E, detached epithelia of the alveoli. Magnified 500 diameters. 



capillaries discernible in the alveolar walls, while those that still 

 remain are very much distended, without being engorged by red 

 blood-corpuscles. The gray color of the lung-tissue is largely 

 due to this loss of capillaries. The plugs in the alveoli are found 

 the more uniformly detached from the alveolar wall, the farther 

 the pneumonia has advanced toward gray hepatization, and in 

 the plugs composed of exudation-corpuscles no coagulated fibrine 

 is discerned. With the new formation of capillary blood-vessels 



