144 



HEMOGLOBIN 



of the logarithm of the percentage saturation of oxyhaemoglobin to 

 the time in the case of a single solution of haemoglobin, it depicts 

 that relation for a number of such solutions, the hydrogen-ion con- 

 centrations of which diflfer. The figure attached to each hne indicates 

 the ^H of the solution to which the hne refers. As the alkalinity 

 increases so the rate of reduction becomes slower, but not xmiformly 

 so; evidently between ^H 6*9 and 7-7 a given change in reaction has 



Fig. 44. Abscissa = time in seconds. Ordinate = oxyh8emoglobin percentage; numerals 

 on left of ordinate axis indicate corresponding value of oxyhaemoglobin per- 

 centage. 



a much greater effect upon the slope of the line than in the more 

 acid and more alkaline regions. Indeed, above ^H 8 increased 

 alkalinity has but httle effect on the velocity constant, and the same 

 is probably true, though the experimental evidence is more meagre, 

 below ^H 5. It is only in the region of the isoelectric point that 

 hydrogen-ion concentration greatly influences the rate at which 

 haemoglobin breaks up. The hydrogen-ion concentration of the 

 blood is, however, about 7-4-7' 6 and is therefore that at which the 

 velocity constant of the reduction phase is most sensitive to tempera- 

 ture. The relation between the velocity constant for the reaction 



095 



HbOa 



Hb-f-Oo 



