346 A YEAR IN SCIENCE 



Internal and external respiration. The process in 

 which the cells of the body take oxygen from the 

 blood, use it for oxidation, and return to the blood 

 waste products is the essential part of respiration and 

 is known as internal respiration. This name distin- 



Lwy*. 



Fig. 162. The respiratory organs. 



guishes it from external respiration, which is purely a 

 mechanical process by means of which air is taken into 

 and given off from the body. 



