THE CARBON DIOXIDE IN BLOOD 



533 



those of oxygen, for it is present in simple solution and in different 

 forms of chemical combination in both the plasma and corpuscles, 

 and is not combined with only one definite substance, as the oxygen 

 is with haemoglobin. Data have already been given to show that 

 the average amounts of carbon dioxide which can be extracted 

 from arterial and venous blood are 43 and 50 volumes per cent. 

 Of these amounts the larger quantity can be extracted from the 

 plasma, and the distribution may be taken as two-thirds in the 

 plasma and one-third in the corpuscles. 



The quantity of carbon dioxide in simple solution is about 

 2 volumes per cent., or 5 per cent, of the total carbon dioxide. 

 The greater part of the gas in the plasma or serum is in loose 

 chemical combination and can be extracted by the blood-pump ; 

 the smaller part is in firm chemical combination, and can only be 

 set free in the pump by the addition of a weak acid. In this 

 respect an important contrast is observed between blood and 

 serum ; all the carbon dioxide can be extracted from the former 

 by exposure to the vacuum alone, the haemoglobin of the red 

 corpuscles acting apparently as an acid. 



The carbon dioxide absorbed by the blood in simple solution 

 follows Henry's law, but the quantity held in chemical combination 

 shows no such simple relation to the pressure. The following data 

 from experiments by Jaquet and Bohr will explain this relationship. 



Absorption of Carbon Dioxide by Blood at 38. 



The next curve (Fig. 30) has been constructed by Bohr from 

 the data just given. 



