DISEASES OF THE PARENCHYMA OF THE LUNG. 



acutely during a pneumonia or hypostatic engorgement, the intervosicular 

 septa are ruptured. On the other hand, if the affection develop slowly, 

 as in a case of adherent pleura, or of tedious catarrh, the vesicular walls 

 undergo a gradual atrophy, growing thinner and thinner, and becoming 

 perforated, until at length several cells coalesce into one large cyst from 

 destruction of their septa. We must decidedly oppose the widely-spread 

 impression that the over-distended cell-walls simply lose their elasticity, 

 without other change of texture ( just as an over-stretched glove or 

 caoutchouc-pipe remains permanently enlarged). That an emphysem- 

 atous lung has lost its elasticity is true, but the above explanation i? 

 false. The loss of elasticity is owing solely to the rupture above men 

 tioned, or to the gradual wasting of the elastic elements of the tissue. 



Substantive emphysema that is, a form of vesicular emphysema, 

 wherein the enlargement of the pulmonary cells is a more primary and 

 independent disease likewise arises, in many instances, in consequence 

 of immoderate and protracted inflation and stretching of the vesicular 

 walls. Laennec, who first pointed out the mode of origin of substantive 

 emphysema, conceived it to be as follows : If, in consequence of catarrhal 

 swelling of the mucous membrane, or owing to viscidity of the bron- 

 chial secretion, an obstacle to the passage of ah* arise in the smaller 

 bronchial tubes, such obstacle may be surmounted during inspiration, 

 owing to the powerful muscular force by which this act is effected; 

 while to expiration, which has fewer auxiliary means at hand, and which 

 is effected mainly through the elasticity of the lung and of the thorax, 

 and through the counter-pressure exerted by the intestines during inspi- 

 ration, such obstacle may prove insuperable. Thus a portion of the air 

 is retained in the vesicles. The next inspiratory act adds more, which, 

 likewise, is unable to escape completely, so that the vesicles are continu- 

 ally becoming more and more over-filled and distended. Two main ob- 

 jections have been advanced against this theory : First, it is replied 

 that the supposition is erroneous that the auxiliaries to inspiration ex- 

 ceed those of expiration at all events, as regards forced expiration. 

 This is true ; yet we have already shown that it is chiefly the larger 

 bronchi which are emptied by a forced expiratory effort, while it has 

 very little action in promoting evacuation of the air-vesicles, especially 

 if the bronchioles be obstructed. It is thus that we account for the 

 common occurrence of permanent vesicular ectasia of capillary bron- 

 chitis. Secondly, it has been urged against the explanation of Laennec. 

 that this hypothesis would be satisfactory if the enlargement of the 

 pulmonary vesicles were no greater in emphysema than the enlargement 

 which they normally undergo in healthy lungs at the height of the in- 

 spiratory act, but that it does not account for the abnormal and excessive 

 distention of the air-vesicles of an emphysematous lung. This argu- 



