214 DISEASES OF THE PARENCHYMA OF THE LUNG. 



or croupous pneumonia may awaken the specific action and thus 

 lead to consumption. 



Tubercle, formerly regarded as the gravest of all the lesions in 

 consumption, is now looked upon as of but secondary consequence ; 

 indeed, it is absent altogether in a majority of cases. 



Fresh tubercle takes the form of a minute, grayish, translucent 

 nodule, having the structure of a lymphoma. It consists of a prolif- 

 eration of cells congregated about minute points of irritation. The 

 cell-growth seems to take place both in the connective tissue and the 

 endothelium. Thus, with the connective tissue, the lymph-vessels 

 and the lymph-sheaths of the finer arteries may be their seat, as well 

 as the walls of the bronchi, the bronchioles, the J>lood- vessels, and 

 their surrounding tissues. Microscopically, a large tubercle consists 

 of many conglomerated nodules clustered around a special centre. 

 The nodule shows a more or less fine net-work (void of vessels), be- 

 tween the meshes of which the cells are enclosed, which latter de- 

 crease in volume as they recede from the central nucleus. At the 

 centre we generally find a few multinuclear giant-cells, which seem 

 like the mother-cells of the tubercle, and by many are regarded as 

 having some specific " tuberculous " property. For want of vessels, 

 tubercle is poorly nourished ; hence, after a brief existence, it either 

 atrophies, shrinking into a hard mass, or else breaks down by fatty 

 change, or else, where great crowded masses of tubercle cause anaemic 

 necrosis and softening of the tissues containing them, cavities are 

 formed. 



Buhl has promulgated the idea that miliary tuberculosis is an 

 infectious disease. As it is generally preceded by a caseous pneu- 

 monia, we may assume that there is an indirect genetical connection 

 between the two conditions ; the more so since, in the rare cases of 

 consumption without cheesy degeneration of the lungs, cheesy de- 

 posits are always found in other organs, especially in the lym- 

 phatics. Moreover, the tubercles are often found only in the closest 

 vicinity of the cheesy deposits ; and, when they are very extensively 

 deposited, the oldest and largest masses, already degenerating, lie 

 nearest to the cheesy foci. 19 ] 



When pneumonia terminates in resolution, the inflammatory 

 product undergoes fatty metamorphosis, then liquefies, and is ab- 

 sorbed. When the disease is followed by caseous infiltration, the 

 fatty metamorphosis is incomplete. The infiltration dries up ; the 

 cells are atrophied ; they lose their rounded form, and shrink, 

 through loss of their water, into irregularly-shaped clots ( Virchow}. 



It is a fact that in the lungs the product of simple inflammation 

 often undergoes caseous degeneration, while in the compact organs 



