GENERAL PART OF EXAMIXATIOX. 49 



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 cmph\sema). 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- 

 bles, may be at the bottom of emphysema of the integument. 



Sometimes after rumenotomy or trocaring, gas passes 

 from the paunch through the muscular wound into the sub- 

 cutaneous tissue. The skin wound having shifted position, 

 the escape of the gas to flie surface is prevented, hence it 

 collects in the loose connective tissue along the back. 



Diseases of the Skin. 



The following terms are most commonly employed to denomi- 

 nate the phenomena of skin lesions: 



1. Spots (maculae) are well circumscribed abnormal colora- 

 tions of the skin. 



