628 
ON EMPHYSEMA OF THE LUNGS. 
a healthy one, and it is unusual to find, even towards the roots 
of the lungs, any trace of the common serous or sanguineous 
infiltrations usually found after death*.” In some cases, how¬ 
ever, especially when the heart is diseased and the pulmonary 
circulation much obstructed, the emphysematous lung becomes 
red and congested. 
It seldom happens that emphysema exists to the extent so 
admirably described in the preceding paragraph, without occa¬ 
sioning the rupture of several of the dilated cells; and it is by 
no means uncommon to find one or more large vesicular cavities 
formed, each by the reunion of all the air-cells of one entire 
lobule, and bounded by its interlobular partitions, which often 
remain uninjured when the texture of the air-cells which they 
enclose is completely destroyed. In extreme cases these inter¬ 
lobular partitions give way likewise, and several lobules are then 
thrown into one large vesicular cavity, resembling more a blad¬ 
der filled with air or the vesicular lung of a frog, than the pa¬ 
renchymatous texture of the human lung. These alterations are 
most frequently observed at the margin of the lung, or at its 
base where it reposes on the diaphragm. 
From these observations it results that emphysema of the 
lung essentially consists in the rarefaction of its parenchyma, 
produced either by the dilatation of its cells, or the rupture of 
their parietes. These lesions may be referred to three principal 
causes;—1. hypertrophy; 2. atrophy; 3. over-distention of the 
air-cells. 
1. Hypertrophy .—Laennec has remarked that in several cases 
where the lung has been rendered incapable of performing its 
functions, the other, having double duty to perform, acquires an 
increase of volume proportionate to its increased activity of 
function. This increase of size appears to result from an in¬ 
crease in the capacity of the capillary bronchi and air-cells, at 
the same time that their parietes are increased in thickness; 
indeed, this is rendered very evident by inflating and drying the 
lung ; for when after this process it is cut into slices, we at once 
perceive some cells much larger than in the natural state, and 
likewise their parietes much thicker than they usually are. The 
state of the air-cells in this form of emphysema may be con¬ 
sidered as analogous to the hypertrophy with dilatation of the 
heart and other hollow muscles. 
2. Atrophy of the lung. —Whenever any cause continues 
for a certain length of time to impede the free entrance of air 
into the pulmonary cells, those cells diminish in number, and 
the parenchyma of the lung falls into a state of atrophy. Ac- 
* Forbes’s Translation of Laennec. 
