i8 CLINICAL DIAGNOSTICS. 



fined. The contained air can be temporarily displaced by 

 applying pressure to parts of the swelling, but as soon as the 

 pressure is released the space caused by it refills. 



Emphysema originating spontaneously is infrequent. It 

 is mostly due to the formation of gas in decomposing blood 

 extravasates or retained abscesses (cmph. scpticum). Spon- 

 taneous emphysema is pathognomonic of black leg, where it 

 appears upon the back, neck, and muscular portions of the 

 legs. 



Emphysema occurs also from the aspiration of 

 air from without into the subcutis. The air may enter 

 through a wound in the skin, or may come from some air- 

 containing internal organ. 



In the first case the air is sucked or pumped into the 

 subcutis through skin wounds which continually shift posi- 

 tion during locomotion. Wounds in the neighborhood of the 

 elbow, therefore, produce emphysema of the shoulder and 

 neck. It is a common practice to treat atrophies of super- 

 ficial muscles ("sweeny") by inflating the overlying skin with 

 air artificially introduced by a bicycle pump or pipe stem] . 

 In the second case the emphysema of the skin has its origin 

 from an internal organ, usually the lung, the alveoli of which 

 are ruptured (interstitial pulmonary emphysema). The 

 course followed by the air is as follows : It passes from the 

 ruptured alveoli into the subpleural connective tissue, making 

 its way to the mediastinum, between which folds it continues 

 to the upper part of the thorax, then following the course 

 of the trachea, large blood vessels and esophagus, it escapes 

 from the pectoral cavity through its anterior aperture into 

 the subcutaneous and intermuscular tissues. Rupture of the 

 pulmonary alveoli may result from a destruction of the lung 

 tissue by pus or putrefaction (gangrene). Rib fractures in- 

 volving the lung, great intra-thoracic pressure from violent 

 coughing, continued bellowing, forced contraction (straining) 

 of the abdominal muscles in bowel, bladder and uterine trou- 



