144 



THE FEEDING OF ANIMALS 



ends in an elongated dUation which is made up of air 

 cells opening into a conunon cavity. These cells are so 

 numerous in the lung tissues that only a very thin wall 

 separates adjoining ones, and in this wall are carried the 



R1G>HT LUNa 



LETT nine 



Fig. 9. Air-tubes of the hiiman lung. (Gerrish.) 



capillaries or fine divisions of the blood vessels leading 

 from the heart. 



205. Object of respiration. — ^The lung structure per- 

 mits the blood to take up oxygen as it flows along and 

 transfer certain wastes into the lung cavities, and thus be 

 made ready to go back to the body carrying a joint load 

 of digested food and oxygen. The air that passes out of 



