RESPIRATION. 355 



usually represented by 50 cubic inches. Abdominal tumors, what- 

 ever their nature and whatever the organ affected, have the constant 

 effect of diminishing the volume of air expired; pregnancy alone 

 has not that consequence. 



If a lung from an animal be thrown into a vessel of water, it 

 floats. If it be forcibly submerged and then squeezed, bubbles of 

 air will find their way to the water's surface. From this little 

 experiment the student knows that, even though the lungs be col- 

 lapsed, yet they contain a certain amount of air which is not very 

 readily expelled. This is the air that is held within the confines of 

 the small alveoli and that cannot very easily find its way through 

 the small passageways opening into them. It follows, then, that all 

 of the air in the lungs cannot possibly be changed during each res- 

 piration, and the amount that is changed beais a very close rela- 

 tionship to the type of respiration, whether it be forced or ordinary. 



1. Tidal Air. The volume of air that is introduced into the 

 lungs during ordinary inspiration by an adult in good health is 

 termed tidal air. It is 20 to 30 cubic inches. 



The tidal air finds its way into and out of only the larger bron- 

 chi, where it comes in contact with the nearly stationary columns of 

 air which extend through the smaller bronchial tubes. The oxygen 

 finds its way into the blood flowing through the capillaries, while the 

 carbonic acid makes its way into the larger bronchial tubes to be 

 finally expelled from the body. 



2. Complemental Air is the quantity of air which we are able 

 to inspire with the greatest effort over and above that of ordinary 

 breathing. The average is estimated by volume as 110 cubic inches. 



3. Reserved Air, or supplemental air, is the quantity of air 

 remaining in the lungs after an ordinary expiration that would be 

 expelled by the fullest effort. It is considered to be about 100 cubic 

 inches. 



4. Residual Air is that which remains in the lungs after the 

 fullest possible expiration and cannot be expelled by any voluntary 

 effort. Its amount depends in great measure on the absolute size of 

 the chest. Its volume is also 100 cubic inches. 



5. The Vital Capacity is the tidal, complemental, and reserved 

 airs added together, and is 230 cubic inches. It represents the 

 amount of air which a person is able to expel from his lungs after 

 the deepest possible inspiration. One-sixth of the air in the lungs 

 is renewed at each ordinary respiration. 



