OXYGEN. 



427 



corpuscles by the increased pressure of the carbon dioxide gas. This 

 author believes that the carbon dioxide expels the hydrochloric acid from 

 sodium chloride by virtue of its mass-action. Sodium carbonate is formed, 

 while the hydrochloric acid, set free, migrates to the blood corpuscles. 

 The reciprocal relation of the plasma and blood corpuscles has not, how- 

 ever, been explained satisfactorily up to date. 



Then, again, has the carbon dioxide tension of the blood any influence 

 upon the absorption of oxygen? We have already seen that the converse 

 is not true, because the carbonic acid and oxygen are combined at different 

 places in the hemoglobin molecule. It has been believed for a long time 

 that the pressure exerted by carbon dioxide in the blood does effect the 

 absorption of oxygen. From the above facts, however, it would seem 

 hardly probable a priori. Bohr, Hasselbach, and Krogh, 1 nevertheless, have 

 shown that as a matter of fact the absorption of oxygen is affected by 

 carbon dioxide pressures, which are not above the physiological values. 

 With increasing carbon dioxide pressures the absorption of oxygen becomes 

 less. A few figures will show how great this effect is: 



Bohr explains this by assuming that the entrance of carbonic acid into 

 the globin molecule changes the affinity of the globin for hematin, and 

 thereby influences the absorption of oxygen by hematin at low oxygen 

 pressures. The biological significance of these discoveries may be ex- 

 plained perhaps as follows : We have already seen that, as regards the gas- 

 exchange with the tissues, it is not the total oxygen contained in the blood 

 which is effective, but chiefly that which is contained dissolved in the 

 plasma; it is this that causes the oxygen pressure of the blood. If now 

 an increased amount of carbon dioxide be produced, then as the hemo- 

 globin cannot hold as much oxygen in combination as before, there will be 

 more oxygen in the dissolved state, so that the oxygen pressure of the 



Zentr. Physiol. 17, 661 (1904), and Skand. Arch. Physiol. 16, 402 (1904). 



