RESPIRATION AND EXCRETION 



331 



glohin 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. -c ^ ■, 



JjToncmal 



of oxygen, 45 to 50 c.c. of Tixbe 



carbon dioxide, and 1 to 2 c.c. 



rroYn. 



^ Jo 

 piumonary 



Diagram to show what the blood loses and 

 gains in one of the air sacs of the lungs. 



of nitrogen. The same amount fi^'^nonaTy 



artery 



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 mostlj^ 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- 

 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 

 bv 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 1.00 



Water vapor (average) 1.40 



Air expired from the lungs contains : — 



Nitrogen 76.95 



Oxygen 15.67 



Carbon dioxide 4.38 



Water vapor 2 



Argon 1 



