RESPIRATION 247 



respired air, it is possible to figure approximately 

 the total amount of oxygen absorbed and carbon 

 dioxide given off during respiration. The minimum 

 daily volume of air breathed is assumed to be 10,800 

 liters and the maximum daily volume 12,240 liters. 

 Thus the minimum daily yolume of oxygen absorbed 

 is 510 liters, maximum 585 liters. Carbon dioxide 

 is exhaled amounting to 473 liters, the minimum 

 daily volume; 520 liters, the maximum daily volume. 



Thus one can readily understand how essential it 

 is for human beings to obtain a fresh supply of air 

 to breathe in order to maintain life and carry on its 

 various activities. Since during every breath the 

 external air loses oxygen and gains carbon dioxide, 

 besides other waste products, the air in dwellings, 

 offices, etc., should be frequently renewed in order 

 to maintain a condition of health. If we take in at 

 each inspiration 30 cubic feet of air, and breathe at 

 the rate of 18 respirations a minute, then in twenty- 

 four hours 450 cubic feet (12.8 cm.) will pass in and 

 out of the lungs. Thus it is easy to understand how 

 a person laboring, or sleeping, etc., in an unventilated 

 room w r ould readily succumb, theoretically, by rebreath- 

 ing the poisoned air from his own lungs. 



The Changes in the Blood during Respiration. 

 The blood as it is forced from the right ventricle of 

 the heart through the pulmonary artery to the lungs, 

 is dark bluish red in color. On reaching the air cells 

 of the lungs the blood becomes bright red in color and 

 is carried through the pulmonary veins to the left 

 auricle, then into the left ventricle of the heart, when 

 it passes out through the large artery (aorta) to supply 

 the body tissues. 



The blood is changed while flowing through the 

 capillaries from <he venous to the arterial state. When 

 the dark bluish-red blood in the pulmonary arteries 

 reaches the capillaries of the pulmonary system where 

 they surround the air cells, and the thin membrane 



