THE DISSOCIATION CURVE OF HEMOGLOBIN 



109 



hydrogen-ion concentration of the solution. The proof as obtained 

 by Cecil Murray and myself of this is as follows : 



Starting from the known facts that the effect of carbonic acid is 

 to reduce the affinity of haemoglobin for oxygen, and that the effect 

 of increased hydrogen-ion concentration is qualitatively the same, if 

 CO2 owes its effect simply to the incidental accumulation of hydrogen 

 ions a given haemoglobin solution of a given cH should have the 

 same affinity for oxygen, whether that concentration of hydrogen 

 ions be established by the addition of COg or of any other acid. 

 This of course assumes that the solutions are similar in all other 



respects. To put the matter in another way, if a solution of haemo- 

 globin be taken and divided into two portions, and if in the case of 

 one portion a number of points be determined in which (a) the 

 percentage saturation of oxygen at a known oxygen pressure is 

 plotted against (b) the cH (or ^^H) — the cH being altered by the 

 addition of HCl — and if in the case of the other portion a similar 

 curve be drawn, but with the cH regulated by exposure to COg, 

 then if COg affects the affinity for oxygen merely by establishing a 

 certain hydrogen-ion concentration, and if HCl does the same, the 

 two curves should be superposable. 



Fig. 33 illustrates the results of such an experiment (7). The gas 

 to which the haemoglobin was exposed was not oxygen but carbon 



vV. 



