58 HUMAN PHYSIOLOGY CHAP, v 



12. The exchange of gases in the lungs through the walls 

 of the capillaries and air sacs is called osmotic action. 



13. Breathing changes the temperature and composition 

 of the air. Rebreathing the same air is dangerous because it 

 contains too little oxygen, too much carbon dioxid and organic 

 poisons. 



14. The average rate of breathing per minute is thirteen 

 when lying down, nineteen sitting, and twenty-two standing. 



15. The presence of carbon dioxid and organic wastes in 

 the blood irritates the nerve cells which regulate the muscular 

 movements in breathing. 



