

THE RESPIRATION 159 



both of the - , must, therefore, be lifted. (Test by 

 experiment.) 



264. Modifications of the Breath. After studying the 

 following list and experimenting with your own breathing, 

 write after each word, I or E, according as inspiration or 

 expiration is chiefly involved in the action. Study each 

 action in other respects also : 



Sighing Coughing Sneezing 



Sobbing Laughing Hiccoughing 



Crying (of a child) Yawning Snoring 



265. Air is composed of a mixture made up chiefly of 

 oxygen, nitrogen and a very small quantity of carbon 

 dioxid. Nitrogen is colorless, tasteless, and odorless ; it 

 does not support combustion, and is one of the most 

 inactive gases known to chemists. The oxygen of the 

 air is also colorless, tasteless, and odorless, but is one 

 of the most active gases known to chemists. The air 

 exhaled contains about the same amount of nitrogen as 

 that inhaled, but it contains much less of oxygen, the latter 

 having been replaced by an almost equal quantity of carbon 

 dioxid. 



266. One Hundred Parts of Pure Air contain about 20 

 parts of oxygen, nearly 80 parts of nitrogen ( and other 

 gases), and .004 of a part of carbon dioxid. Air com- 

 ing from the lungs contains 16 parts of oxygen, nearly 

 80 parts of nitrogen, and over 4 parts of carbon dioxid. 

 The air while in the lungs has lost four parts of its oxygen, 

 there has been no change in the quantity of nitrogen, and 

 it has gained four parts of carbon dioxid. The oxygen is 

 in the air in order to supply an element to animals essential 

 to their activity. The nitrogen in the air is not used in the 

 body. The small amount of carbon dioxid in the air sup- 

 plies the plants with carbon. Its quantity is being constantly 

 added to by fires and by the breath of animals. The leaves 



