QUANTITY OF AIR BREATHED 



295 



The reserve air is that which may be expelled by a forcible and deeper 

 expiration, after an ordinary expiration, such as that which expels the 

 tidal air. The reserve air amounts to from 1,200 to 1,500 cc. This is also 

 termed the supplemental air. 



FIG. 235. Photograph of the Sanborn Company form of spirometer. The grad- 

 uated disc records the volume of air exhaled. In using the spirometer the reservoir is 

 first filled with water to form a water seal for the air chamber. To perform a respi- 

 ratory volume test the instrument is set automatically at zero, though it is well to 

 begin with the air chamber empty. Place the previously sterilized mouth piece between 

 the lips and if necessary, close the nostrils with pinch cock or with the hand. The 

 receiving chamber is delicately balanced and as the breath is forced through the tube into 

 this bell it rises, recording the movement on the circular index, from the scale of which 

 the volume is read off directly. For very accurate comparative determinations the 

 expired air should be allowed to stand long enough to come to constant temperature, 

 and corrections for variations from the standard temperature and pressure should be 

 made. This is not necessary in the routine laboratory and gymnasium measurements. 



The residual air is the quantity which still remains in the lungs after 

 the most violent expiratory effort. Its amount depends in great measure 

 on the absolute size of the chest, but may be estimated at about i ,000 cc. 



tO 1,200 CC. 



The quantity of air breathed per minute, called the minute volume, 

 varies in the adult at rest according to size. But the average may be set 

 down as between 5 and 8 liters. In 24 hours this would amount to from 



