THE DISSOCIATION CURVE OF HEMOGLOBIN 



95 



namely p + j^. It remains for us to find out what the relation of 



Cji to p is. 



Consider the special case in which C^ = 100, i.e. all the haemoglobin 

 is reduced haemoglobin, 



/ 1 \ ^ 100 



100 = 



p= 0. 



100 



The distance AB (Fig. 24) in that case = ^ . Hence the distance 

 from BB' of any point on the hyperbola is a measure of the pressure. 



xA' e 



Fig. 24. 



We have therefore derived the following information from the law 

 of mass action. If the reaction is a chemical one involving single 

 molecules only, the relation of the okygen pressure to the percentage 

 of oxy- to totial haemoglobin is capable of beihg represented as a 

 rectangular hyperbola, the origin of which is at once the point at 

 which there is no pressure of oxygen and no oxyhaemoglobin, and 

 the curve approximates to a line representing complete saturation. 

 If now we turn back to Fig. 22 we shall see that the curve which we 

 have shown as representing the relation of the pressure of oxygen 

 to the percentage of oxyhaemoglobin is identical with the curve we 

 have just given, and therefore the law of mass action is to this extent 

 satisfied. 



