HEAT IN RELATION TO THE HUMAN BODY 15 



water in a tub or sink remove the stopper. Holding the 

 inverted jug tipped sufficiently, let one end of a rubber tube 

 be put up through the neck of the jug. Have some one 

 of the class fill his lungs to their utmost capacity, and then 

 through the tube force out into the jug as far as possible all 

 air from the lungs, withdrawing the end of the tube from 

 the jug before taking the other end from the mouth. 



Keep the mouth of the jug under water and replace the 

 stopper to retain in the jug all the water not displaced by 

 the exhaled air. Remove the jug from the water, set it right 

 side up, and by use of a graduate ascertain the volume of 

 air expelled from the lungs by measuring the quantity of 

 water needed to refill the jug. 1 [Lung capacity is tested 

 most satisfactorily by use of a spirometer.] 



6. In like manner, and as average of several trials by 

 the same person, determine the volume of a natural (not 

 forced) exhalation. 



7. From the results above, calculate what per cent of 

 the air capacity of the lungs was used in once breathing. 

 Infer a good purpose served (a) by an occasional long, deep 

 breath ; (6) by not having the lungs emptied of all air at 

 every breath. 



8. From the data above calculate the volume of air taken 

 into the lungs (a) per minute; (b) per hour. About one 

 fifth of this is oxygen. 



Calculate how long it would take the individuals present 

 in the room to breathe as much air as the room contains, 

 using the same air but once. 



1 1000 c.c. (1 liter) is equivalent to about 64 cubic inches. 



