288 DISEASES OF THE PLEURA. 



m which the disease has resulted from a rupture of dilated emphysom- 

 atous subpleural pulmonary vesicles. 



The majority of cases of traumatic pneumothorax are not, as a 

 rule, the result of entrance of air into the pleural sac, through a mere 

 penetrating Around of the thoracic wall, but of a stab or gun-shot 

 wound, which also involves the pulmonary pleura, thus permitting the 

 escape of air from the lung into the pleural sac. In fracture of the 

 ribs, it sometimes happens that the pulmonary pleura is lacerated by 

 spicula of bone, causing pneumothorax, without perforation or appre- 

 ciable wound of the wall of the chest. A gradual perforation of the 

 pulmonary pleura, by ulceration of its external surface, is a much more 

 frequent occurrence than this acute traumatic perforation. As we have 

 already stated, the bursting of an empyema into the lungs and its 

 evacuation through the bronchi take place in a similar manner. After 

 a certain amount of pus has been discharged by the coughing-fit which 

 follows the perforation of the empyema, a corresponding quantity of 

 air naturally enters the sac with the next inspiratory act. The pyo- 

 thorax is thus converted into a pneumo-pyothorax. In this form of 

 disease the air scarcely ever passes freely into the pleura, but merely 

 enters a space firmly bounded by adhesions, by which the empyema is 

 incapsulated, and which separate it from the rest of the cavity, a con- 

 dition to which we shall allude again while discussing the symptoms. 



We have already stated that all perforations of the thoracic wall 

 do not cause pneumothorax. If the track of the wound through the 

 wall of the chest be tolerably narrow, and if its direction be oblique, 

 the integument forms a sort of valve at its outer end, which prevents 

 the air from entering the chest. It is the same with the fistulous 

 passages, which usually remain after the spontaneous external opening 

 of an empyema. On the contrary, if the thoracic wall be penetrated 

 perpendicularly, and the opening be sufficiently large, pneumothorax 

 does occur, air flowing in and out of the pleura, through the orifice, aa 

 the chest heaves and falls. It may be mentioned, finally, that in ex- 

 ceedingly rare instances, pneumothorax arises through the perforation 

 of the pleural sac by ulceration or degeneration of growths within the 

 stomach or oesophagus. 



ANATOMICAL APPEARANCES. The existence of pneumothorax may 

 often be guessed upon simple inspection of the cadaver, owing to the 

 enormous distention of one or other side of the chest, with obliteration 

 or prominence of the intercostal spaces. If the abdomen be opened 

 first, we find that the convexity of the diaphragm faces downward, 

 and that the liver or the spleen is deeply displaced. If a knife 01 

 trocar be thrust into the distended side of the chest, the ah* gushes out 

 witn a hissing sound, capable of extinguishing a light held before the 



