INTERNAL ORGANS. 



teriial surface of the ribs, and the external sur- 

 face of the lungs, did not the air rush in 

 through the windpipe, and so distend its 

 branches and cells as to make the lungs com- 

 pletely fill the cavity. Thus are the lungs con- 

 stantly employed in inspiration and expiration ; 

 and this process, which we call breathing, is car- 

 ried on by the combined action of the diaphragm, 

 and the muscles of the ribs aiid abdomen. It 

 is supposed that the elasticity of the lungs, 

 or rather of the branches of the windpipe, 

 materially contributes to this important action, 

 in the same manner as a bottle of elastic gum, 

 or Indian-rubber, fills itself either with air or 

 water, from its great elasticitj^ If a small 

 pipe or quill be tied to the m.outh of one of 

 those bottles, and the air pressed out by the 

 hand; as soon as the pressure is removed, 

 the bottle will resume its oritrinal form, and 

 consequently be filled with air again. If the 

 mouth of the bottle or the pipe be put into 

 water after the air has been pressed out, on 

 removing the pressure, the bottle will be filled 

 with water. 



