RESPIRATION 



Capillaries upon the sides of an air sac 

 (X 200). 



changes in the sounds he can tell what is the matter with 

 the lungs. 



149. What air does to the blood. The air is four fifths 

 nitrogen and one fifth oxygen gas. Both gases go into the 

 air sacs of the lungs, but 



all the nitrogen comes 



back, while some of the 



oxygen is left behind, and 



some carbonic acid gas 



and water are put in its 



place. We must see what 



becomes of the oxygen. 



Upon the sides of the air 



sacs is a close network of 



capillary blood tubes. 



Their sides are very thin. 



While they keep the blood 



from running out, they let oxygen gas pass through very 



easily. The red blood cells are oxygen carriers, and as 



they shoot through the capillaries they take tiny loads of 



oxygen and carry it to 



aU parts of the body 



for the use of the cells. 



Each load of oxygen 



causes its red blood cell 



to become bright red in 



color, and so the whole 



blood becomes a brighter 



red as it passes through 



the lungs. 



150. How air reaches the cells of the body. From the 

 lungs the blood goes to the left side of the heart and is 

 sent through the capillaries to all parts of the body. 



Diagram of the respiration of cells. 



