The dissociation curve of haemoglobin 



19 



If we write y for C R and x for ( p + ^ j , we obtain the relationship 



xy = & constant, namely -~- . If we now construct a curve plotting y 



vertically and x horizontally, and observing the condition that for 

 any point the product of x and y must be constant, we obtain a 

 curve known as a rectangular hyperbola (Fig. 8). 



This curve does not at first sight relate the concentration of 

 reduced haemoglobin (R) to the pressure p, but to something else, 



namely p + -^ . It remains for us to find out what is the relation 



A 



Of CR tO p. 



B' 



O 



100 . 



A B 



FIG. 9. 



Consider the special case in which C R = 100, i.e. all the haemo- 

 globin is reduced haemoglobin, 



^ 100 

 JR ~ K ' 



The distance AB (Fig. 9) in that case = Hence the distance 



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



We have therefore derived the following information from the law 



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



22 



