RESPIRATION AND EXCRETION 



331 



globin of the red corpuscles. Changes taking place in blood are 

 obviously the reverse of those which take place in air in the 

 lungs. Every hundred cubic centimeters of blood going into 

 the lungs contains 8 to 12 c.c. 

 of oxygen, 45 to 50 c.c. of 

 carbon dioxide, and 1 to 2 c.c. r 



rTorn, 

 puLmonary 



ariery 



pulmonajy 



of nitrogen. The same amount 

 of blood passing out of the 

 lungs contains 20 c.c. of oxy- 

 gen, 38 c.c. of carbon dioxide, 

 and 1 to 2 c.c. of nitrogen. 

 The water, of which about 

 half a pint is given off daily, 

 is mostly lost from the blood. 



Changes in Air in the Lungs. 

 Air is much warmer after 

 leaving the lungs than before 

 it enters them. Breathe on 

 the bulb of a thermometer to 



prove this. Expired air COn- Diagram to show what the blood loses and 



gains in one of the air sacs of the lungs. 



tains a considerable amount 



of moisture, as may be proved by breathing on a cold polished 

 surface. This it has taken up in the air sacs of the lungs. The 

 presence of carbon dioxide in expired air may easily be detected 

 by the limewater test. Air such as we breathe out of doors con- 

 tains, by volume : 



Nitrogen 76.95 



Oxygen 20.61 



Carbon dioxide 03 



Argon '-,.. v 1.00 



Water vapor (average) . . . 1.40 



Air expired from the lungs contains : 



Nitrogen ... ..... . , * > > ^ - - : 76.95 



Oxygen . . . , . v ; . . . . 15.67 



Carbon dioxide . -. . .''.. . . . . . . .* . . . '*.; 4.38 



Water vapor .V v . 2 



Argon ...... 1 



