282 HUMAN PHYSIOLOGY 



sary to overcome the atmospheric pressure and create 

 a vacuum. Students of physics will recall the Magde- 

 burg Hemispheres. A wound which pierces the human 

 thorax may admit air between the two layers of the 

 pleura and permit the collapse of a lung, giving rise to 

 a condition known as pneumothorax. This can happen 



FIG. 69. To suggest the absence of connection between the lungs 

 and the walls of the chest. (See text.) 



to one lung without seriously affecting the situation of 

 the other. 



A collapsed lung is practically useless. It no longer 

 follows the movements of the chest as the normal lung 

 does. Instead it remains of a nearly constant volume 

 and the little air which it contains is not renewed. 

 Recovery from one-sided pneumothorax is possible. 



