206 PHYSIOLOGY FOR DENTAL STUDENTS. 



shows that 100 c. c. contains about 45 to 50 c. c. of carbon diox- 

 ide, and that the gas exerts a pressure or tension of about 40 mm. 

 mercury, which is equal to about five per cent of an atmosphere. 

 Now water will dissolve under these conditions about 2 1 / c. c. of 

 carbon dioxide per 100 c. c. This would leave the most of the 

 carbon dioxide of the blood unaccounted for, in case the blood 

 has the same solvent power for the gas that water has. The rest 

 of the carbon dioxide therefore must be accounted for as being 

 in chemical combination with the constituents of the plasma and 

 corpuscles. The major part is probably held in the form of 

 sodium carbonate and bicarbonate, the remainder being combined 

 with the proteins of the plasma and the red corpuscles. The most 

 satisfactory explanation of the manner in which carbon dioxide 

 is dissociated from the above mentioned compounds in the blood, 

 is that there are substances in the plasma, such as the blood pro- 

 teins, which act as weak acids, and gradually drive off the carbon 

 dioxide when, as in the air in the lungs, its escape is rendered 

 easy by a lowered carbon dioxide pressure outside the plasma. 



