EMPHYSEMA OF THE LUNG, 113 



ineiit ought to have prevented the confusion which exists between per- 

 manent inspiratory ectasis and emphysema of the lung. Permanent 

 inspiratory ectasis may subside completely ; and, indeed, after removal 

 of the obstacles to expiration, often does so subside. (These are the 

 cases of so-called recovery of emphysema of the authors.) But, if per- 

 manent inspiratory vesicular inflation be kept up for any great length 

 of time, the continuous strain and expansion produce structural 

 changes in the vesicular icalls. They atrophy, grow thin, become per- 

 forated, several vesicles blend into one larger cyst, and then emphysema 

 really commences. 



This account of the origin of substantive emphysema, from immod- 

 erate inspiratory expansion and stretching of the vesicular walls, is not 

 applicable to all cases, however, and there are a good many instances in 

 which we must give credit to the expiratory theory. It is easy to un- 

 derstand how emphysema may arise in the upper part of the lungs as a 

 result of often-repeated forcible expiration with simultaneous contraction 

 of the glottis. In severe paroxysms of coughing, such as occur in 

 whooping-cough and chronic bronchial catarrh, the thorax is vigorously 

 contracted, while, at the same time, the escape of air is impeded by con- 

 striction of the glottis. In straining, and in playing upon wind-instru- 

 ments, the same process occurs. So, too, in lifting heavy weights, and 

 in other severe bodily exertions, the ah* is compressed within the thorax, 

 and only allowed to escape at intervals, and with a groaning or panting 

 sound. In all these acts contraction of the chest is effected by vigorous 

 upheaval of the diaphragm. The result is the expulsion of a strong 

 current of air from the lower bronchi, the direction of which is obliquely 

 upward, and, if the air be prevented from escaping through the larynx, 

 a portion of it, in a compressed state, must be driven into the upper 

 bronchi, whose direction is obliquely downward. By the centrifugal 

 pressure exerted, by the air thus compressed, upon the vesicles of the 

 upper lobes of the lung, and upon the adjacent thoracic wall, the latter 

 become distended as far as it is possible for them to yield. In a vigor- 

 ous man, whom I have had under observation, and in whom the pecto- 

 ralis minor and a larger portion of the pectoralis major were absent, I 

 have been able to see that, both in coughing and straining, so much air 

 was forced into the upper part of the lung as to cause prominence ol 

 the upper intercostal spaces ; and I have often noticed and pointed out 

 the same phenomena, though in a lesser degree, in patients with thin 

 muscles, and but little subcutaneous fat. 



The occurrence of emphysema, in patients who have not been ex- 

 posed to any of the causes hitherto mentioned, is rare, but the fact is 

 certain. Hence, in a small number of cases, it would seem that the 

 third of the above theories of the origin of emphysema is the correct 

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