176 



APPLIED PHYSIOLOGY 



which suck venous blood toward the heart just as it sucks 

 air into the lungs. 



306. Pulmonary circulation. As the blood enters the 

 veins from the capillaries, it has lost some oxygen and 



gained carbonic 

 acid gas and other 

 waste matter. This 

 makes it much 

 darker in color. 

 Before it is used 

 again it is purified 

 and given a new 

 supply of oxygen. 

 For this purpose 

 it is sent to the 

 lungs as soon as it 

 reaches the heart. 

 From the veins 

 the blood flows in- 

 to the right side 

 of the heart, and 

 then to the lungs 

 through the pul- 

 monary artery. 

 The pulmonary 

 artery divides 

 again and again 

 into small twigs, 

 and these divide 

 into a close net- 

 Diagram of the course of the blood in the circulation. work of cap iH ar ies 



within the lungs, where the blood is separated from the air 

 by only the thin walls of the capillaries. Through these 



