COMBINING POWER OF HEMOGLOBIN WITH OXYGEN 



293 



the amount of oxygen that was combined was very great per unit of in- 

 creased pressure at the low pressures, but relatively less at the higher 

 pressures. Or, which amounts to the same, if hemoglobin saturated with 

 oxygen be subjected to decreasing oxygen pressure, it sets free the combined 

 oxygen, at first slowly, then more rapidly. By consulting the typical curve 



too 



80 



70 



60 



50 



30 



20 



10 



/ 



10 



20 



30 



FIG. 239. Dissociation curves of oxy hemoglobin in: 1,0.7 P er cent, sodium chlor- 

 ide; II, in sodium bicarbonate, and III, in disodium phosphate. The figures along the 

 ordinates represent percentages of saturation of hemoglobin by oxygen. The figures 

 along the abscissae represent mm. of oxygen pressure in mercury. (Bancroft and Camis.) 



showing this relation, it will be evident that the critical partial oxygen pres- 

 sures influencing this combination fall at about 30 to 35 mm. mercury of 

 oxygen tension and below. See figure 238. 



A number of factors influence the dissociation of oxygen from hemoglobin 

 at a given oxygen tension. Of prime importance is the influence of the 

 presence of carbon dioxide gas as shown by Bohr and recently confirmed by 

 Bancroft and Camis. With an increase in the tension of carbon dioxide 

 there is a decrease in the fixation of oxygen. 



