340 DISEASES OF THE RESPIRATORY ORGANS. 



Etiology : The diplococcus pneumonice is found in the inflam- 

 matory exudates and in the sputum ; it is the micro-organ- 

 ism most frequently associated with the disease, though the 

 pneumococcus of Friedlander, streptococcus, staphylococcus, 

 typhoid bacillus, and bacillus of influenza seem to be capable 

 of producing similar lesions. 



The lower lobe of the right lung is most frequently affected. 



Division of process : The inflammatory process may be di- 

 vided into three stages : engorgement, red and gray hepati- 

 zation. 



In the stage of engorgement, or congestion, the affected area 

 is deep red in color, crepitates less and is somewhat firmer 

 than normal, but is not solidified, does not sink if placed in 

 water ; the overlying pleura is dull and lustreless. On sec- 

 tion a bright red, frothy fluid exudes on pressure. 



Microscopically the capillary bloodvessels of the alveolar 

 walls are greatly distended with blood and encroach some- 

 what upon the air-spaces, within which are a large number of 

 red blood-corpuscles, and a few leukocytes and desquamated 

 epithelial cells. A similar exudate is seen in the smaller 

 bronchi. 



In the stage of red hepatization the inflammatory exudate 

 which has poured into the air-spaces has coagulated and com- 

 pletely solidified the lung-tissue, giving it a liver-like consis- 

 tency. On pressure the affected area does not crepitate, is 

 firm to the touch, yet friable, and if placed in water sinks. 

 It is swollen, and upon the external surface the ribs have left 

 an imprint. The pleura is often coated with a fibrinous exu- 

 date. On section the surface is bright red, smooth and 

 glistening ; later, as the fibrinous plugs within the air spaces 

 contract, the surface, especially if torn, has a granular appear- 

 ance, and with a little care the projecting alveolar plugs may 

 be lifted or scraped from the air-spaces, of which they form a 

 perfect mould. 



Microscopically the air-vesicles are completely filled, even 

 distended, with the inflammatory exudate. The exuded blood- 

 serum has coagulated, and the fine fibrillse of fibrin entangle 

 within their meshes a large number of red blood-corpuscles 

 and migrated leukocytes and a few epithelial cells derived 

 from the swollen and proliferating epithelium of the alveolar 



