4 GOOD HEALTH 



This shows the difference between oxygen and car- 

 bon dioxid: one is our friend, the other our enemy. 

 Fortunately, in fresh, outdoor air there is always much 

 oxygen and little carbon dioxid. 



A change comes, however, in the rooms where people 

 live and breathe, for when you take a deep breath of sweet, 

 pure air the lungs use up a part of the oxygen at once ; 

 and when you expel the air from your lungs, carbon 

 dioxid is there in place of the oxygen. The exchange 

 is made inside the lungs. 



It is plain, then, that breathing takes oxygen out of the 

 air and puts carbon dioxid in its place. 



If a man is in a very small room, and if no fresh air 

 can get in from anywhere, his breathing will change the 

 air in the room so much that if he stays there long enough 

 he will die. One of the saddest cases of this kind was in 

 India when the British and Hindoo soldiers were right- 

 ing each other. Finally the Hindoos captured one hun- 

 dred and forty-six British prisoners and put them into 

 a room that was about twenty feet square. It had two 

 small windows, so that a little air did manage to get 

 in; but there was not enough of it for so many people. 

 Fresh air could not enter fast enough to give the men 

 the oxygen they needed, and the air that was in the 

 room grew worse and worse until everybody suffered 

 and gasped for breath, and when morning came only 

 twenty-three of the men were alive. The rest had died 



