116 DISEASES OF THE PARENCHYMA OF THE LtJNG. 



more puffed up and inflated, when exposed to the atmospheric pressure, 

 than do healthy lungs. Since emphysematous lungs, as they do not 

 contract, retain about the same volume when the chest is laid open as 

 they did when it was closed, we may further understand why, m cases 

 of wide-spread and especially of substantive emphysema, in which, 

 during life, the dimensions of the lungs had been abnormally large, 

 there should also be found an increase in their size, when exposed post 

 mortem. This increase in the volume of the lungs, as we shall show 

 by-and-by, is the result of an increase in the capacity of the thorax, 

 arising in part from depression of the diaphragm, and in part from an 

 elongation of the costal cartilages, and a peculiar direction of the ribs. 

 If an emphysematous lung were to contract like a normal lung, this in- 

 crease in size would disappear if the chest were cut into; actually, 

 however, it persists even after the lungs have been removed from the 

 body. 



In the circumscribed vicarious emphysema about indurated or 

 atrophied parts of the parenchyma, we find groups of tender vesicles, 

 varying in size from that of a hemp-seed to that of a pea. They are tightly 

 inflated, and always traversed by a delicate network, a remnant of the 

 intervesicular septa. The seat of circumscribed vicarious emphysema is 

 most frequently at the apex of the lungs. 



When vicarious emphysema has arisen acutely, during a pneumonia 

 or hypostatic engorgement, or chronically as in pleural adhesion, the 

 affection is limited to the anterior and lower edge of the lungs. This 

 will be readily understood, after the explanation of its pathogeny given 

 above. On the other hand, where the disease is a result of closure of 

 any of the bronchi, the seat of the cellular dilatation is not so constantly 

 at the anterior and lower edges, and often occupies the apices and other 

 regions. A characteristic of this variety is, that inflated emphysematous 

 portions of lung exist alongside of collapsed and shrunken parts. Such 

 lungs, when removed from the chest, often present a very irregular con- 

 tour, which does not at all correspond with that of the thoracic cavity. 

 The emphysematous parts are prominent, and may even appear almost 

 bulbous or pedunculated, while the collapsed region is marked by deep 

 depressions and rigid bands. If inflated, it of course assumes the shape 

 of the cavity of the chest, the hard cords and the pedicles of the bul- 

 bous portions retract into the interior, and the projections and lobes 

 created by the depressions crowd together. 



If the substantive emphysema arise from forced expiration and con- 

 stricted glottis, its seat is always in the upper lobes of the lung and par- 

 ticularly in the apices. Where it proceeds from protracted inspiratory 

 strain, the vesicular distention is distributed more or less evenly through- 

 out the whole organ, and it is a characteristic of this variety, when re- 



