THE BLOOD GASES 335 



of nitrogen. The partial pressure of the oxygen therefore is .21 X 760 = 159.6 

 mm. Hg., and that of nitrogen is .79 X 760 = 600.4 mm. Hg. The absorption 

 of oxygen into water takes place then under a pressure of 159.6 and that of 

 nitrogen under a pressure of 600.4 mm. Hg. 



B. When the liquid exercises a chemical attraction for the gas, it is not 

 only absorbed physically, but is combined chemically. We have, however, to 

 distinguish two cases, according as the chemical combination does or does not 

 depend upon the partial pressure of the gas. If it does not, the whole quantity 

 of gas will be absorbed whatever the pressure. If it does, that is, if the com- 

 bination between the liquid and the gas is a function of the gas pressure, the 

 combination will gradually become less and less as the partial pressure dimin- 

 ishes, and with a partial pressure of zero will cease entirely on account of dis- 

 sociation. In the latter case, therefore, just as when the absorption is purely 

 physical, the quantity of gas entering a liquid is a function of the pressure, 

 but with the important difference that there is here no direct proportion between 

 the volume absorbed and the pressure. 



When a liquid has stood for a long time in contact with a certain volume 

 of mixed gases until it has become saturated with the different gases in the 

 mixture, the tension of each gas in the liquid is equal to its partial pressure in 

 the surrounding space. If the partial pressure of any one gas becomes less, the 

 liquid gives off just enough of this gas to establish equilibrium once more, and 

 vice versa. 



In order to determine the tension of gases in a liquid, the liquid is placed 

 under a definite pressure in contact with a mixture of gases previously analyzed, 

 and, after a certain time, the mixture is again analyzed. The tension of any 

 gas in the liquid is equal to the partial pressure of this gas in the surrounding 

 space, if at the end of the experiment its partial pressure is the same as it was 

 before. In order to hasten the equalization of tensions, the liquid can be shaken 

 up with the mixture of gases, or may be allowed to flow through them in a 

 fine stream. 



2. THE BLOOD GASES 

 A. NITROGEN AND ARGON 



These gases are only absorbed physically in the blood. The coefficient of 

 absorption for nitrogen at the temperature of the body is about 0.013-0.02 

 and the content of nitrogen and argon together is in the neighborhood of 

 2 vols. per cent ; according to Regnard and Schloessing the blood contains some 

 0.04 vols. per cent of argon. 



When the air pressure is very much increased, as in diving and in caisson 

 work, the quantity of nitrogen taken up by the blood must be considerable. If 

 the pressure is removed rapidly, the nitrogen (the other gases of the blood in 

 part also) passes suddenly over into the form of a gas and air emboli are formed 

 in the vascular system, which may cause more or less serious disorders or even 

 death (Hoppe-Seyler, Bert). The gas collected from the heart in such cases 

 consists of about eighty per cent nitrogen. 



B. OXYGEN 



After Lothar Meyer had demonstrated that the oxygen content of the 

 blood presents but slight variations with diiferent partial pressures, whence 



