RESPIRATORY SYSTEM 



351 



presence of some air in the lungs all the time makes it 

 possible for the exchange of gases in the blood to take 

 place continually instead of at intervals. 



Rib. 



Fig. 166. Diagram showing the position of the ribs and diaphragm 

 in A, expiration ; B, inspiration. 



Comparison of inhaled and exhaled air. The oxygen 

 of the air which is inhaled diffuses through the thin 

 walls of the air sacs and capillaries in the lungs and 

 enters the blood. Most of it combines with the hemo- 

 globin in the red corpuscles and is thus carried to the 

 different cells of the body, where it is given up again. 

 As a result of the oxidation which then takes place the 

 energy which we need is produced, and also, as in any 

 burning, waste products are formed. Of these waste 

 products the principal one removed by the lungs is 

 carbon dioxide. 



