224: DISEASES OF THE PARENCHYMA OF THE LUNG. 



alveolar walls of their nutritive fluid, and causing them to perish and 

 break down. Perhaps the anaemia and necrosis of the pulmonary tissue 

 are favored in severe cases by an extension of the process of prolifera- 

 tion of cells from the surface into the tissues themselves. 



If the cell-growth be not of sufficient volume seriously to compress 

 the vesicular walls and their vessels, the caseous masses gradually 

 become still more inspissated, and the shrunken atrophied cells 

 break down into a detritus. Little by little their organic matter dis- 

 appears, while calcareous salts are deposited until there finally is left 

 a chalky or mortar-like concretion. In other cases, again, the arrested 

 fatty metamorphosis of the cells is reestablished ; they become lique- 

 fied, and capable of reabsorption. 



While one or other of these processes is progressing in the cellular 

 elements involved in the caseous degeneration, an extensive prolifera- 

 tion of the connective tissue is going on in the lung. The calcified 

 deposits are incapsulated, and the space rendered vacant by the cells, 

 which have suffered fatty degeneration and liquefaction, is filled up by 

 connective tissue. In such cases, the lung-substance does not again 

 become penetrable by the air, but is converted into a dense callous 

 mass ; and as the connective tissue, which continues to shrink more 

 and more, occupies less room than the healthy parenchyma which it 

 replaces, the lung becomes reduced in size and the thorax sinks in. 

 But, as depression of the thorax can only take place to a limited extent, 

 the bronchi become dilated into rounded and elongated cavities. This 

 is the most common form of cavity in phthisis where it runs a chronic 

 course. The absorption of the caseous masses, through supplementary 

 fatty degeneration and liquefaction, may be so complete that, upon dis- 

 section, we may find nothing except pulmonary tissue in a state of 

 induration from interstitial pneumonia, perfectly void of air, traversed 

 by (bronchiectatic) cavities, and without a trace of caseous deposit. 

 While the apex of the lung usually contains cavities of greater or 

 less capacity, and while a large portion of its upper lobes is solidified 

 partly by gelatinous or caseous infiltration, and in part through indu- 

 ration and consolidation upon section of the remainder of the lung 

 which still remains permeable to the air, the small points of induration 

 before alluded to are almost always found projecting above the sur- 

 face of the cut in the shape of yellow nodules. We must beware of 

 immediately assuming such minute solid spots to be tubercles. Ex- 

 perience teaches that many objects which at the first glance seem to 

 be miliary tubercles, and which were formerly regarded as such, prove, 

 upon closer examination, to be transversely-divided bronchi with case- 

 ous contents, or bronchi surrounded by alveoli, with thickened walls and 

 infi trated with caseous matter. By avoiding such errors in post-mor* 



