DISEASES OF THE LUNGS. 157 



inflated ; does not crepitate under the fingers, and is very 

 friable, breaking down readily with a soft fracture. The 

 cut surface has a distinctly granular appearance, seen espe- 

 cially when the lung-tissue is torn. This appearance is 

 due to the coagulated matter which plugs up the alveoli. 



During this stage there appears to be but little alteration 

 in the walls of the vesicles, or in the epithelium lining 

 them ; the latter, however, is usually swollen and granular, 

 and the alveolar walls often have a few leucocytes adhering 

 to them. The pleura covering the solid lung is always more 

 or less inflamed, and is opaque and coated with an exudation 

 of lymph. 



In the third stage, or that of grey hepatization, there is 

 continuance of the emigration of the white cells, which 

 escape from the vessels and gradually accumulate in the 

 pulmonary alveoli. The epithelial cells lining the alve.olar 

 walls become more swollen and granular, and their air- 

 vesicles become filled with cells, so that the fibrous exuda- 

 tion is no longer visible as an independent material, as in 

 the second stage. 



The cells soon undergo rapid fatty changes, and the fibrin- 

 ous material breaks down. Thus the alveoli as usually seen 

 are filled with granular elements, and their walls, though 

 usually unaltered, may be partly disintegrated. The weight, 

 density, and friability of the lung now become greater than 

 in the stage of red hepatization, although the granular 

 aspect of the cut surface is much less marked. 



The lung-tissue is soft and pulpy, and a purulent fluid 

 exudes from the cut surface. 



The lung itself changes in colour from a dark red-brown 

 to a grey or yellowish -white. 



Terminations of Acute Pulmonary Inflammation : — 



(A.) Resolution. — This is by far the most common and 

 favourable termination of croupous pneumonia. 



