68 ELEMENTARY PHYSIOLOGY 



because it is robbed of the life supporting oxygen, 

 but because one of the gases which are expelled from 

 the body, by the breath, acts like a poison when it is 

 inhaled (re-breathed) again. 



Ventilation means the furnishing of the 



Ventilation. 



needed supply of pure air. Nothing is 

 more important in the line of hygienic or health pre- 

 cepts than this, that we should avoid the breathing 

 of air which has been made impure by the breath. 

 To avoid this, it is necessary to have, at all times, 

 a proper interchange between the air of a room and 

 the pure, free air without. No person can remain 

 long in a closed room without being injured by his 

 own breath. There must be a place of escape for 

 the impure air and a place of entrance for the pure 

 air. Since impure air rises toward the top of a 

 room, it escapes best from the opening of a window 

 at the top, while pure air enters best through an 

 opening lower down. But without attempting to 

 describe any of the numerous plans of ventilation, 

 let this precept suffice: Get from the abundance of 

 pure air which God has provided, as Etuch as you 

 can at every breath, and avoid, as a poison, the inha- 

 lation of impure air. 



THE VOICE. 



The organs of the voice are so closely connected 

 with the respiratory system that we will give a 

 brief description of them here. 



