MECHANISM OF EMPHYSEMA. 
594 
The freedom from oedema and from morbid deposits, when 
other parts of the lung are so affected ; the absence of accu- 
mulation in the bronchi, or, at least, its comparatively slight 
character, allowing of the perfect and easy inflation of the em- 
physematous parts when others are collapsed ; finally, the 
habitual seat of emphysema in those parts of the lung which are 
usually most exempt from other disease, — all tend to prove 
what I have now stated. The diminished elasticity, the dry- 
ness, the ansemia, which have all of them been supposed to be 
the predisposing cause of this lesion, are manifestly nothing 
more than the effects of the distention with air upon the circu- 
lation and nutrition of the compressed walls of the delicate pul- 
monary air-cells. Even the small accumulations of granular 
deposit found by Mr. Rainey may be accounted for by these 
secondary nutritive changes. 
But emphysema is not merely a lesion resulting from in- 
ordinate distention of previously sound portions of lung; it is, 
as we have already seen, the product of mechanical derange- 
ment in the sound parts of lungs otherwise diseased . The ex- 
istence of bronchitic condensation, of induration, of concretions, 
&c., if not a necessary cause of the production of emphysema in 
the sound air-vesicles, is at least in some way related to it. The 
theory of emphysema by Laennec, besides the objections offered 
to it in the former part of this memoir, in no way accords with 
the facts now adduced. Mucous obstruction of the bronchi, 
even if proved to exist, cannot determine, directly, both con- 
densation and rarefaction of the lung; and we have already 
learned, from unquestionable and multiplied evidence, which of 
these two is its real result. The opinion of Louis, derived, ap- 
parently, chiefly from a consideration of the seat of election of 
emphysema as compared with that of bronchitis, is opposed to 
the idea of any precise relation between these two affections ; 
but this negative opinion would appear to be sufficiently an- 
swered by the numerical facts above adduced. 
Some writers, conceiving, like Laennec, that emphysema 
is produced in the act of expiration, believe it to be the result 
of violent efforts of coughing, or other forcible expiratory acts. 
But have we really any direct proof whatever that cough, how- 
ever violent, or any similar act, can produce emphysema, apart 
from the other accidents of bronchitis ? In croup, in laryngitis, 
in aneurism of the aorta, we have cough even more violent and 
distressing than that of bronchitis ; yet these affections are not 
known usually to cause emphysema, and I have repeatedly seen 
cases opposed to the idea of their having any such influence. 
The alleged unusual frequency of emphysema among players of 
wind-instruments is likewise totally devoid of proof, and rests 
