512 



THE RESPIRATORY SYSTEM. 



develop as the result of fresh infections of the lung through the lym- 

 phatics or otherwise. These areas or nodules may coalesce so that whole 

 lobes or parts of lobes of the lungs may become consolidated (Plates VII. 

 and VIII. ). Microscopically, these consolidated areas may be composed 

 of tubercle tissue more or less necrotic, with partial or total obliteration 

 of the walls of the air spaces. On the other hand, when the process has 

 been exudative as well as productive in character, one may see in the solid 



FIG. 294. -AN AIR VESICLE FILLED WITH FATTY EPITHELIUM, i\ CHRONIC PULMONARY TUBERCULOSIS. 

 The wall of the air vesicle is diagrammatic. 



areas the outlines of the air vesicles and larger spaces; but these, 

 together with the enclosed exudate, may be necrotic and granular with 

 few stained nuclei and fragments of chromatin. Much of the exudate 

 which fills the air vesicles either within or about these more densely con- 

 solidated areas may not be caseous or necrotic, but may consist of well- 

 preserved or fatty epithelial cells (Fig. 294), or of these with varying 

 quantities of leucocytes and fibrin. 



Aside from these complex forms of nodular and diffuse tuberculous 

 lesions one may recognize a Diffuse Exudative Tuberculous Inflammation of 



