198 



APPLIED PHYSIOLOGY 



way help in raising the chest wall are called into play, 

 and the expenditure of muscular energy becomes very 

 great, equivalent, it has been calculated, to raising a 

 weight of 300 pounds. In forced expiration the abdo- 

 minal muscles are largely made use of to press up the 

 liver and other viscera against the under surface of the 



FIG. 13. VERTICAL SECTION OF THE BIGHT LUNG TO SHOW 

 EXPANSION. (KEITH.) 



diaphragm, which has been relaxed by the pulling down 

 of the lower ribs. Hence the capacity of the chest is 

 lessened both laterally and vertically. 



The air which is still left in the lungs after the fullest 

 expiration, and which is only displaced when the chest 

 wall is opened, is termed 'residual.' It amounts to 

 about 100 cubic inches for the two lungs. When the 



