ANIMALS. 137 



smaller, until they become a multitude of minute tubes, 

 called capillaries, passing through every part of the body. 

 At length these again gradually unite in veins (v, v, v\ 

 through which the blood is returned to the heart. It is 



Arteries, Capillaries, and Veins. 



then sent out through another set of tubes, which con- 

 duct it through the lungs, where it is brought in con- 

 tact with the air taken into the lungs in breathing, 

 becomes purified, returns to the heart, and starts again 

 on its original course. 



