200 APPLIED PHYSIOLOGY 



Even the supplemental air only gives another two 

 minutes' supply, for the most expert pearl-divers cannot 

 stay longer under water than that. 



The complemental capacity of the lungs is made use 

 of by a man who fills his chest preparatory to swimming 

 under water ; the supplemental by a singer in sustaining 

 a prolonged note. 



If the chest be filled as completely as possible, and 



! Complemental 

 Tidal 

 Reserve 

 Residual 



FIG. 14. DIAGRAM OF VITAL CAPACITY. (AFTER HUTCHINSON.) 



then squeezed as empty as the expiratory muscles can 

 squeeze it, the volume of air expelled is the measure of 

 the vital capacity. The vital capacity is thus a gauge of 

 the efficiency of respiration or of the vital activity of the 

 lungs. In health it amounts to about 225 cubic inches, 

 but varies greatly with age, size of chest, etc. Tall 

 people have a greater vital capacity than short,* and, 



* For every inch of stature between 5 and 6 feet, 8 additional 

 cubic inches of air are given out by a forced expiration. 



