244 AIR. 



carbonic acid gas, (in the same way as 

 burning fuel, (see pp. 33, 36). 



Q. What becomes of the NITROGEN of the 

 air, after the oxygen enters the blood ? 



A. The nitrogen is exhaled, and 

 taken up by the leaves of trees and 

 other vegetables, (seep. 35). 



Q. Wliy does the vitiated air (after the 

 oxygen has been absorbed) COME OUT of the MOUTH, 

 and not sink into the stomach ? 



A. The vitiated air (being heated 

 by the heat of the body} ascends naturally, 

 and passes by the heavier fresh air 

 (which we inhale) without obstruction 

 or injury. 



Q. If (both in combustion and in respiration) 

 the OXYGEN of the air is CONSUMED, and the 

 NITROGEN REJECTED Why are not the PROPOR- 

 TIONS Of the AIR DESTROYED ? 



A. Because the upper surface of 

 vegetable leaves (during the day) gives out 

 oxygen and absorbs nitrogen, and thus 

 the proper balance is perpetually 

 restored. 



Q. Show how God has made ANIMAL and 



VEGETABLE life DEPENDENT OU each Other ? 



