kl-.si'lRATION 



diffuse-, into the blood and is taken up by the luemoglobin, so 

 that this is all converted again into oxyluvmoglobin. 



In this way the air in the lungs gains carbonic acid and 

 loses oxygen. 



Changes in the Air. Put some clear lime water into a 

 bottle and by means of a tube blow the air you expire through 

 it. In a short time the lime water becomes " milky." This is 

 because the lime takes up carbonic acid from the expired air, 

 and carbonate of lime is formed as a white precipitate. If 

 you suck ordinary air through 

 lime water, no milkincss, or 

 only a very little, is produced. 

 This shows that air that has 

 been taken into the lungs 

 IKI-, gained a quantity of 

 carbonic acid. If two bottles 

 containing lime water are 

 arranged as in Fig. 5 i , breath- 

 ing can be carried on natur ^ 



ally through the tube C, the 



inspired air coining in through 



A, and the expired air going out through li. A remains clear, 



B becomes milky. 



Ordinary atmospheric air breathed into the lungs contains 

 in 100 volumes about 



Nitrogen . . . . 79.0 volumes 

 Oxygen .... 20.9 ., 



Carbonic acid gas . . .04 



and a variable amount of water in the form of aqueous vapour. 



The air expired from the lungs contains in 100 volumes about 

 Nitrogen .... 79 volumes 

 Oxygen . . . 16 



Carbonic acid gas . . 4 ,, 



There is therefore a loss of 4 or nearly 5 per cent of oxygen 

 and a gain of 4 per cent of carbonic acid gas. The tempera- 

 ture of the atmospheric air varies very much, but the expired 

 air is at, or nearly at, the temperature of the body (98" K.), 

 whatever that of the air inspired is. The expired air is 

 always saturated with aqueous vapour. When the tcmpera- 



FIG. 51. 



