PNEUMOTHORAX. 289 



orifice. The gas which escapes consists principally of carbonic acid 

 and nitrogen, and contains but little oxygen. Its quantity varies, but 

 is usually sufficient to produce the monstrous dilatation of the chest 

 above alluded to. It is rare for the pleural sac to contain air alone. 

 Even though the patient only survive the pneumothorax a day or two, 

 pleurisy develops, and we find sero-purulent or purulent exudation in 

 the pleura besides the air. The quantity of the effusion is variable, 

 and generally is largest when the pneumothorax is of longest standing. 

 Again, the effusion may almost fill up the pleura, while the amount of 

 air it contains may be very small. Finally, all the air may disappear 

 from the sac, so that it contains nothing except the effusion. 



Whether the pleura contain air alone, or both air and pleuritic exu- 

 dation,- the lung is compressed into a very small volume, completely 

 void of air, and is pushed up against the spinal column. And it is 

 only when it is partially attached by adhesions to the thoracic wall 

 that it occupies any other position. In many cases it is only with great 

 trouble, and by inflating the lung under water, that the point of perfo- 

 ration, which is usually covered by fibrinous deposit, can be discovered. 

 In other instances the orifice is already closed. Besides the above- 

 mentioned downward displacement of the diaphragm, a considerable 

 lateral displacement of the heart and mediastinum is generally found 

 in pneumothorax. 



Many important variations from the anatomical alterations de- 

 scribed above take place when uniform retraction of the lung on all 

 sides is prevented by extensive and firm adhesions of the pleural sur- 

 faces. Sometimes the air which has escaped is contained in spaces of 

 small capacity, and enclosed by adhesions upon all sides. Then, only, 

 the adjacent parts of the lung are compressed, and the thorax is only 

 partially dilated ; the liver and heart are not displaced. This latter condi- 

 tion is the rule in pneumothorax from perforation of an empyema, but it 

 occasionally is met with also in cases of perforation of a superficial cavity. 



SYMPTOMS AND COURSE. The symptoms of pneumothorax are 

 generally very striking and characteristic, and are easily understood, 

 if we bear in mind the consequences which necessarily must ensue after 

 perforation of the pulmonary pleura, or of the thoracic wall. 



The pleural cavity being no longer hermetically sealed, the lung 

 retracts by virtue of its elasticity. A retraction of the lung, such as 

 we find upon opening the thorax upon the dissecting-table, occurs 

 during life, at the moment when the air enters the pleural sac through 

 a perforation, either externally or internally. Even the lung of the 

 uninjured side retracts as far as the mediastinum can yield to the 

 traction, now exerted upon one side of it alone. Immediately after 

 the establishment of the pneumothorax, the cavitv only contains the 

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