8 



GOOD HEALTH 



Turn now to grass and trees. Notice the green leaves 

 as they flutter in the sunshine. You would not suspect it, 

 but even while you watch them they are at work. Each 

 separate one is indeed taking carbon dioxid from the air 

 and is uniting it with water to make food for itself ; and 

 later the food becomes part of the plant. Also, while 

 these changes go on, the plant gives 

 off some of the oxygen which is freed 

 from the carbon dioxid. 



Now this part of plant life goes on 

 only in the light. But continually, by 

 night as well as by day, plants also 

 breathe by taking in oxygen and by 

 giving off carbon dioxid. The truth is, 

 that even though they have no lungs, 

 breathing is as necessary to plants as 

 it is to ourselves; for, whether they 

 are in the sunshine or in total dark- 

 ness, they depend on oxygen as much 

 as we do. Other things use oxygen too. 



Light a small candle, set over it a glass jar that fits 

 down flat on the table, and watch the flame. At first 

 it will burn as brightly as ever; then it will grow more 

 and more dim, until at last it will go out entirely. If you 

 should now put a mouse or bird into the jar, it would 

 die at once, because the oxygen in the jar has been used 

 up by the candle. 



USING UP THE OXYGEN 



