RESPIRATION AND EXCRETION 



385 



part the movement is beyond our control. 

 The nerve centers which govern inspiration 

 are part of the sympathetic nervous system. 

 Anything of an irritating nature in the trachea 

 or larynx will cause a sudden expiration or 

 cough. When a boy runs, the quickened res- 

 piration is due to the fact that oxygen is used 

 up rapidly and a larger quantity of carbon di- 

 oxide is formed. Thus the nervous center 

 which has control of respiration is stimulated 

 to greater activity, and quickened inspiration 

 follows. 



Problem LII. A study of the prod- 

 ucts of respiration. {Laboratory Man - 

 ual, Prob. LII. ) 



Vnlii [ihnH'titiil 

 Air 



II 1(1 Cll. ill. 



Tidal Air 



■ ill cu. in. 



Jii-srrrc 

 Air 



lull I'll. ill. 



Rcsicliial 



?^()i=?== 



L^30 

 CU. in. 



Diagram showing the relative 

 amounts of tidal, comple- 

 mental, reserve, and resid- 

 ual air. The brace shows 

 the average lung capacity 

 for the adult man. 



Changes in Air in the Lungs. — Air is 

 much warmer after leaving the lungs 

 than before it enters them. Breathe on 

 the bulb of a thermometer to prove this. 

 Expired air contains a considerable 

 amount of moisture, as may be proved 

 by breathing on a cold polished surface. 

 This it has taken up in the air sacs of 

 the lungs. The presence of carbon di- 

 oxide in expired air may easily be de- 

 tected by the limewater test. Air such as we breathe out of doors 

 contains, by volume : — 



Nitrogen 79 



Oxygen 20.96 



Carbon dioxide . 04 



Air expired from the lungs contains : — 



Nitrogen 79 



Oxygen 16.02 



Carbon dioxide 4.38 



Water 60 



In other words, there is a loss of between four and five per cent 

 oxygen, and nearly a corresponding gain in carbon dioxide, in 

 expired air. There are also some other organic substances present. 



HUNT. BS. BIO. — 25 



