ON EMPHYSEMA OF THE LUNGS. 
629 
cordingly; we find this atrophy invariably taking place in lungs 
which have been compressed by pleuritic effusions of long stand¬ 
ing, or when the principal bronchial tube is compressed by ex¬ 
ternal tumours. In old age, likewise, the lungs sometimes 
undergo so considerable a degree of atrophy, that the chest is 
visibly contracted in consequence; and in such persons they 
are small, contain very little blood, are remarkably light, anil 
their whole texture appears rarefied. If we inflate and dry a 
lung in this state, we perceive a remarkable alteration in the 
disposition of the ultimate bronchial ramifications, and of the 
air-cells in which they terminate ; they no longer form distinct 
cavities, separated from each other by complete septa: at first 
these septa are only reduced to a state of extreme tenuity, but 
at a later period some of them appear perforated in one or more 
points, while others seem ruptured and irregularly torn. In 
some cases the walls of the cells disappear altogether, and we 
only find in their stead some delicate filaments traversing in 
different directions cavities of various sizes. In the parts of the 
lung where these alterations exist, there are no longer to be 
found either bronchial ramifications, or air-cells, properly so 
called, but merely vesicles of greater or less diameter, divided 
into compartments by imperfect septa or irregular laminae, bear¬ 
ing a perfect resemblance to the lungs of cold-blooded animals*. 
Thus we see how lesions the most opposite in their characters, 
hypertrophy and atrophy, may alikfe produce this disease. But 
in the case of hypertrophy there is only dilatation of the cells 
without laceration of their parietes, unless as an accidental 
occurrence ; w'hereas, in atrophy of the lung, large cavities are 
formed by several cells being thrown into one by the extenuation 
and rupture of their walls. Hence arises this important differ¬ 
ence, that in the first case the number of surfaces on which the 
blood is exposed to the action of the air remains the same, 
while in the second the number of these surfaces is considerably 
diminished. It is easy to see that the respiration will not be 
equally affected in these tw r o cases, and that the dyspnoea must 
necessarily be more considerable in the latter. There is, how¬ 
ever, one circumstance that occurs in old age (at which period 
this alteration, as already stated, most generally occurs) which 
prevents the respiration from being as much embarrassed as we 
might, a priori, have expected,—namely, the diminution that 
takes place in the quantity of the blood, or (what comes to the 
same thing) the diminution in the rapidity of the circulation. 
For this reason atrophy of the lung, when occurring in old age, 
should rather be regarded as a natural phenomenon resulting 
* Andral’s Pathological Anatomy. 
