414 LECTURE XVIII. 



exerted by the gas in question may be accurately computed), and the liquid 

 shaken with this gas mixture for some time. Now, according as the gas 

 contained in the liquid exerts a less pressure, the same pressure, or a greater 

 pressure, than is exerted by the same gas in the gas mixture, there will be 

 either an increase, no change, or a diminution in the amount of the par- 

 ticular gas above the liquid. 



Let us now come back to the question of the condition of the oxygen 

 as it circulates in the blood. According to the above principles, it ought 

 to be easy to decide whether there is any chemical combination between 

 the oxygen and the blood. From the amount of oxygen in the air that is 

 breathed into the lungs, or, what is the same thing, from the partial pressure 

 of the oxygen in the alveolar air, taking into consideration the temperature 

 of the body and the composition of the blood, we can compute how much 

 oxygen the latter could take up by simple absorption. 

 . There are a number of different methods which are derived from the 

 above principles for determining the gas content of a liquid. Since with 

 rise of temperature the amount of gas absorbed diminishes, it is evident 

 that the gas can be expelled from a liquid by heating it. When the liquid 

 begins to boil, i.e., when it is itself being converted into vapor, all of the 

 absorbed gases have been expelled. The pressure of the gas in the liquid 

 is now equal to zero, whether it is due to the fact that there is a complete 

 vacuum above the liquid, or because the gas which was absorbed by the 

 liquid has been replaced by some other gas (e.g., water vapor) in the 

 atmosphere directly in contact with the liquid. According to the above 

 description of the behavior of gases, the effect in the latter case, as far as 

 the absorption of the gas goes, must be exactly the same as if all the gases 

 had been removed, for then the partial pressure of the given gas in contact 

 with the liquid would have become zero. 



The air that is breathed into the lungs contains in round numbers 79 

 per cent by volume of nitrogen, 21 per cent oxygen, 0.03 per cent of carbon 

 dioxide, and varying amounts of water vapor. If we compare the amount 

 of oxygen taken up by the blood in the lungs, with that computed to be 

 present from the partial pressure of the oxygen in the gas mixture that 

 reaches them, it is found that far too much oxygen is removed by the 

 blood, so that it is quite out of the question to consider the phenomenon 

 as one of simple absorption. 1 Nitrogen and argon, which, as far as we 

 know, take no part in the metabolism of the living animal organism, behave 

 quite differently when in contact with the blood. They are, for the most 

 part, merely absorbed mechanically. The absorption coefficient for nitro- 

 gen amounts at the body temperature to about 0.013 to 0.02. Oxygen, 

 however, in its absorption by the blood, in no way follows the gas laws. 

 The amounts of oxygen absorbed by the blood, when it is exposed to differ- 



1 Cf. Hiifner: Arch. Anat. Physiol. 1890, 1; 1895, 209. 



