94 ELEMENTARY PH YSIOLOGY. 



THE 



The excretory functions of the lungs 



Impurities J 



Thrown off (Turn to manikin of the body, 8, 9.) 

 e Lungs. j iave b een referred to under Respira- 

 tion, and their structure there explained. The pure 

 air, taken into the lungs, gives up its life-giving 

 oxygen, and in return becomes heavily loaded with 

 carbon dioxide, or, as it is more commonly called, 

 carbonic acid gas. 



The chief of the excretions fcrom the 

 moxide lungs is carbon dioxide. It is a re- 



sult of the union of the oxygen of the 

 air inhaled, and carbon from the tissues of the body. 

 This compound will not only fail to support life, 

 but is an actual poison. 



The destructive nature of this gas is 

 illustrated in many ways. As for in- 

 stance, if a man goes down into a well 

 and is overcome, becomes unconscious and helpless, 

 it is this gas which causes his condition. It is of 

 the same kind as that which is thrown off by the 

 lungs, is colorless, and is heavier than air, and conse- 

 quently settles to the floor, or into cellars, wells, etc. 

 Therefore it is safer to sleep on a bed than on the 

 floor, since this deadly gas settles, during the night, 

 on the floor. 



As it will not support life in man and animals, so 

 it will not support combustion, or burning. Hence, 

 if it should become necessary to go down into a well, 



