420 



LECTURE XVIII. 



from the tissues, there is more of this gas. The following table will give 

 some idea of the amounts of the separate gases in arterial and venous 

 blood. 1 



The venous blood from different vascular regions shows an extremely 

 varying content of the different gases. The carbon dioxide content of all 

 the venous blood taken as a whole, must be represented by that of the 

 right heart; for it is here that the venous blood coming from the whole 

 vascular system is mixed. Schoffer, 2 working in Ludwig's laboratory in 

 1860, compared the composition of arterial blood with that of the right 

 heart. The following table gives the results obtained by Bohr and 

 Henriques. 



If we compare the amount of carbon dioxide present in arterial blood 

 with that in venous blood, it is at once apparent that it cannot be a case of 

 simple absorption. The quantity present is far too large. Like oxygen 

 it must be chemically combined for the most part. The amount of carbon 

 dioxide absorbed by the blood does in fact depend upon the pressure of the 

 gas, with which it is in equilibrium; but the absorption is not proportional 

 to this pressure, as it would be in a case of simple absorption. With what 

 substance in the blood is this gas combined? The relations here are far 

 more complicated than in the case of oxygen. With the latter there is 

 but one kind of combination, that with hemoglobin. Carbon dioxide, 

 however, combines with different substances in the blood. A part of 



1 Christian Bohr: Handbuch, loc. cit. p. 83. 



2 Sitzungsberichte d. Wiener Akad. 41, 613 (1860). C. Ludwig: Mediz. Jahrbucher, 

 Wien, 1865. N. Zuntz and Hagemann: Erganzungsband III zu der landwirtschaftl. 

 Jahrb. 27 (1898). 



