RESPIRATION. 



103 



Exchanges between the Air and the Blood in the 

 Lungs. Whatever the air coming from the lungs cen- 

 tains that was not in the air entering them, it has taken 

 from the blood, and what the air has lost it has given to 

 the blood. The air in the air vesicle is separated from the 



BRONCHIAL TUBE 



FROM PULMONARY ARTERY 



TO PULMONARY VEIN 



Fig. 46. Exchanges between the Air and the Blood in the Lungs. 



blood in the pulmonary capillaries only by the thin wall of 

 the air vesicle and the thin capillary wall. Carbon dioxid, 

 water, and other waste matters pass from the blood through 

 this thin partition into the air vesicle, to be sent out by 

 later expiration. Oxygen from the air in the vesicle passes 



