314 



HISTOLOGY OF THE MORBID PROCESSES. 



gray (Fig. 272, a). In favorable cases a stage of " resolution " fol- 

 lows that of gray hepatization ; the fibrin disintegrates, and the 

 exudate becomes softened (Fig. 272, 6) and is expectorated. This 

 is not the invariable outcome. Sometimes the fibrinous exudate is 

 replaced by new-formed fibrous tissue, granulation -tissue, develop- 

 ing from the alveolar walls, and the alveoli become obliterated. The 

 process in that case is similar to that which affects the pleura. 



The pleural surface over the parts of the lung which are the seat 

 of the pneumonia is usually also the seat of a similar inflammation ; 

 but here the course of the process is a little different. There are 

 fewer red blood -corpuscles and less serum in the first exudate that 

 is formed, probably because the proximity of the bloodvessels to 

 the pleural surface is less immediate than the corresponding rela- 

 tions in the pulmonary tissue (Fig. 277). The exudate therefore 



FIG. 277. 



c bed Ic 



E 



Sfo<*3 ' 



# 



*J 



ML 



Exs 



Fibrinous pleurisy, ten hours after its inception. (Abramow.) Lg, lung, in which three 

 alveoli are shown in section. These contain an exudate, consisting chiefly of red blood- 

 corpuscles and fibrin in somewhat granular form. In the alveolar walls are capillaries 

 containing either red corpuscles or leucocytes. ML, membrana limitans of the subendo- 

 thelial areolar tissue ; E, endothelium with nuclear chromolysis ; F, fibrin ; Ic, leuco- 

 cytes; D, mass of red corpuscles, fibrin, and leucocytes, the latter with polymorphic 

 nuclei ; a, &, c, red corpuscles in various stages of decolorization and disintegration ; D 

 and F make up the exudate upon the pleural surface; Exs, exudate in the pulmonary 

 alveoli. 



first appears as a layer of fibrin upon the surface of the pleura. This 

 may subsequently disintegrate and be absorbed, or granulation-tis- 

 sue may develop from the pleura beneath it and grow into the fibrin, 

 causing its gradual absorption and replacement with fibrous tissue. 



