38 PHYSIOLOGY FOR NURSES 



air entering and leaving the infundibula and alveoli. If 

 the air vesicles are filled up, or the listening is done 

 over large bronchi, the second is modified and becomes 

 tubular. It is the difference in sound caused by the air 

 moving in small tubes and large ones. 



Quantity of Air. The total quantity of movable air 

 in the lungs of an average man is about 230 cubic inches. 

 Of this amount about 20 cubic inches is taken in at each 

 inspiration, about 110 cubic inches can be taken in after 

 an ordinary inspiration and about 100 cubic inches is 

 the amount which can be forcibly expelled after an or- 

 dinary expiration. The amount passing in and out in 

 each ordinary respiratory cycle is called tidal air, that 

 taken in by forced inspiration, complemental air and 

 that which can be expelled by the greatest effort supple- 

 mental. Tidal, complemental, and supplemental air to- 

 gether constitute one's vital capacity. 



Not the utmost effort will expel all the air from lungs 

 which have once been filled, a fact which causes lung 

 tissue to float in water, which no other tissue will do. 

 The fact that once filled lung tissue floats and that never 

 filled sinks, often enables experts to determine whether 

 a dead child has ever breathed or was born dead. The 

 air remaining after fullest expiration is termed residual 

 air and amounts to about 100 cubic inches. 



Number of Respirations. Within the limits of health 

 respirations may vary from sixteen to twenty-four per 

 minute, or one respiration to four heartbeats. In child- 

 hood breathing is more rapid and at all ages it varies 

 with exercise or the position of the body, while in feb- 

 rile diseases the rate greatly increases. Some patho- 

 logic conditions diminish the rate. 



Modifications of Respiration. When breathing is dif- 

 ficult for any reason it is termed dyspnea, from two 



