54 Chapter V 



who were the discoverers of the influence of carbonic acid on the 

 dissociation curve. 



Carbonic acid however is not specific in its effect. Lactic acid 

 acts in precisely the same way (2) ; so also do mixtures of lactic and 

 carbonic acids. 



Having made the rough statement that the effect of acidity is to 

 reduce the effective concentration of oxygen, I must now state more 

 precisely (1) what I mean by "reaction," and (2) what I mean by 

 reduction of the effective concentration of oxygen. 



It seems that the influence of acids depends on the change in 

 hydrogen ion concentration which they cause in the blood : and this 

 appears to be different from the change of hydrogen ion concentration 

 which they would cause in water or salt solution. 



For instance, mineral acids in equal molecular concentration are 

 generally much more powerful than acids such as lactic, acetic or 

 carbonic. They cause a much greater concentration of hydrogen 

 ions. Yet when they are added to serum the change in the hydrogen 

 ion concentration which they produce is nearly the same. This change 

 has been measured by the method of titration with an indicator which 

 changes colour gradually over a considerable range of hydrogen ion 

 concentrations. 



Added to normal salt solution the following strengths of acid 

 would produce equal changes in the hydrogen ion. concentration : 



Lactic Hydrochloric Formic Acetic 



M/200 = M/300 M/80 



M/110 = M/200 M/130 M/50 



M/50 M/170 



M/10 M/130 



But the relative quantities of these acids which produce equal 

 changes in hydrogen ion concentration in serum are 



Lactic Hydrochloric Acetic C0 2 Hydrogen ion cone. 



M/200 M/200 10- 6 ' 8 



M/100 M/120 10- H-1 

 M/100 weaker than M/100 



2 / = exposure to atmosphere of 100 % 10- 4 ' 



These results were obtained by titration with the indicator 

 referred to above. 



Now so far as the affinity of the haemoglobin for oxygen is con- 

 cerned, the same change is wrought by increasing the concentration 



