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TEXT-BOOK OF PHYSIOLOGY 



which is stature. It is found that between 5 and 6 feet the capacity in- 

 creases 8 inches (130 c.c.) for each inch increase in height. 



The Total Volume of Air Breathed Daily. For the solution of certain 

 problems connected with ventilation it is necessary to determine the total 

 volume of air taken into the lungs in the course of 24 hours. This can 

 be determined approximately if the two factors, the average volume of air 

 taken into the lungs at each inspiration, and the average number of res- 



FIG. 195. GAD'S PNEUMATOGRAPH. 



pirations per minute be known. If it be accepted that the inspired volume 

 varies from 328 to 492 c.c. and that the respiratory frequency averages 18 per 

 minute, then the total volume breathed would amount to from 8500 to 

 12,752 liters. 



The volume changes of the thorax indicated by the volumes of air en- 

 tering and leaving the lungs can be not only determined but graphically 

 represented by means of an apparatus similar in principle to the spirometer, 

 devised by Gad and known as the pneumato graph or aeroplethysmo graph 



FIG. 196. DIAGRAM REPRESENTING THE VOLUME CHANGES OF THE THORAX AND LUNGS. 



(Modi-fled, jrom Boruttau.) 



(Fig. 195). This consists of a quadrangular box with double walls, the 

 space between which is filled with water. The center of the box is an air 

 chamber. A thin walled mica box sinks into the water. Posteriorly it is 

 attached to and rotates around an axis, which permits of an elevation or 

 depression of the anterior portion. It is also carefully counterpoised. A 

 light lever attached to the mica box records its movements. The interior 

 of the box communicates by a tube with a large reservoir into which the 

 individual breathes, the object being to prevent a too rapid vitiation of the 



