220 



A MANUAL OF PHYSIOLOGY 



in it is read off. This gives the volume of the expired air at atmo- 

 spheric pressure. Similarly, by breathing air from the spirometer 

 the amount inspired can be measured (p. 291). 



From 400 to 500 c.c. of air* 

 are taken in and given out 

 at each respiration in quiet 

 breathing. This is called tidal 

 air. It amounts to 35 pounds 

 by weight in twenty-four 

 hours, or enough to fill, at 

 atmospheric pressure, a cubical 

 box with a side of 8 feet. 

 With the deepest possible in- 

 spiration room can be made 

 for 2,000 c.c. more ; this is 

 called complemental air. By 

 a forced expiration 1,500 c.c. 

 can be expelled besides the 

 tidal air ; and to this quantity 



FIG. IOI.-DIAGRAM OF SPIROMETER. the name of supplemental or 

 A, vessel filled with water. B, glass reserve air has been given. 

 cylinder with scale c, swung on pulleys After the deepest expiration 

 and counterpoised by weights w. D, t h er e always remains 1,000 



tube for breathing through. r . . ,-, 



to 1,200 c.c. of air in the 



lungs (Durig), and this is called the residual air. After a 

 normal expiration following a normal inspiration the lungs 

 still contain stationary air to the amount of about 2,500 c.c. 



The term 

 vital or res- 

 p i r ato r y 



ia 



ilemt nft/i 



R\csidual air 



FIG. 102. DIAGRAM TO ILLUSTRATE THE RELATIVE AMOUNT OF 

 COMPLEMENTAL, TIDAL, SUPPLEMENTAL, AND RESIDUAL AIR. 



capacity is 

 applied to 

 the quantity 

 of air which 

 can be ex- 



11 rl h thp 

 P 6j DVtI 



deepest ex- 



piration following the deepest inspiration, and amounts in an 

 adult of average height to 3,500 or 4,000 c.c. The maximum 

 quantity of air which the lungs can contain is evidently equal 

 to vital capacity plus residual air. At one time the vital 



* The average obtained by the writer for 8 1 healthy students, with an 

 average body-weight of 66 kilos, was 460 c.c., or 7 c.c. per kilo. In 4 new- 

 born children the tidal air varied from 20 to 30 c.c., and from 7-6 to 7-3 c.c. 

 per kilo, which is not very different from the amount in the adult. The 

 pulmonary ventilation must therefore be far more rapid in the child, since 

 its respiratory frequency is so much greater. 



