AIR, 



27. Air a Necessity of Life. 



There can be no life of any sort without air. Ani- 

 mals breathe it and plants need it, in order to live. There 

 is air even in water and fishes could not live without 

 this air. We live in an ocean of air which surrounds the 

 whole earth and this ocean is called the atmosphere. The 

 meaning of the word "atmosphere" is breath-sphere. Do 

 you think that the atmosphere is well named? 



Experiment 35. Holding the Breath and Deep 

 Breathing. 



a. See how many seconds you can hold your 

 breath. You should be able to hold it one minute, with 

 practice. 



b. Stand erect with the chest up, without having 

 any of your muscles hard and take just as long a breath 

 as you can, breathing through the nose. When you 

 think that you cannot draw in, or inhale, any more air, 

 contract all the muscles of the body, and hold the breath 

 for a few seconds. Slowly let the air come out. Letting 

 the air out is called exhaling. Repeat several times and 

 then see how long you can hold your breath. Always 

 take this exercise before holding your breath. Why can 

 you hold it longer than you did at first? 



Experiment 36. *The Effect of Depriving a Plant 

 of Air. 



* Adapted from Farmers' Bulletin 408, U. S. Dept. of Agriculture. 



