THE BLOOD GASES 339 



serum. It should be added, however, that the curve of C0 2 absorption for 

 the corpuscles exhibits a much greater dependence upon the partial pressure 

 of C0 2 than that for the serum (Bohr). The constituent most actively 

 concerned here again is the haemoglobin (Fig. 132). 



Hcemoglobin therefore can combine carbon dioxide as well as oxygen. We 

 are not yet clear just how this takes place. Bohr has shown that the absorp- 

 tion of carbon dioxide by hemoglobin free of alkalies is influenced little 



FIG. 132. The absorption of carbon dioxide in a solution of haemoglobin, after Bohr, 



1.76 per cent solution; 3.8 per cent solution. The abscissae represent the pres- 



sure to which the gas was subjected, the ordinates the amount of carbon dioxide in c.c. 

 absorbed by 1 g. of haemoglobin. 



or not at all by oxygen. For this reason he assumes that the two gases are 

 combined with different parts of the haemoglobin molecule the oxygen with 

 the pigment nucleus, and the carbon dioxide with the proteid component. 



D. THE QUANTITY OF BLOOD GASES 



The content of gases is very different in arterial and venous blood. Anal- 

 yses of the gases in dog's blood, carried out under the direction of Ludwig and 

 Pfliiger, give us, according to the summary of Zuntz, the following average 

 percentages : arterial blood, 18.3 vols. per cent oxygen and 38.3 vols. per cent 

 carbon dioxide. By very rapid extraction of the gases Pfliiger obtained for 

 arterial blood 22.6 vols. per cent oxygen and 34.3 vols. per cent carbon dioxide. 

 Merely by standing, therefore, the blood uses up oxygen and forms carbon 

 dioxide. From arterial human blood Setchenow obtained 21.6 vols. per cent 

 oxygen and 40.3 vols. per cent carbon dioxide. The percentage of oxygen and 

 carbon dioxide in arterial blood moreover exhibits considerable variations. 



The content of gases in venous blood depends naturally upon the velocity 

 of blood flow and upon the activity of metabolism. That the blood gases 

 exhibit great variations in the different vascular regions, according as the 

 organs are more or less active, is quite beyond question. But at present we have 

 analyses of only the mixed blood from the right heart and from the central 

 veins. These give us, according to the summary of Zuntz, as compared with 



