THE SPECIFICITY OF HEMOGLOBIN _ 47 



Pressure of 

 Animal Temperature half-saturation 



Man ... 15° C. y^gg mm. 



Arenicola ... 16° C. y^StJ "^^' (^PP^^^^^i^^^^j) 



Whilst the latter of these determinations is not very accurate it is 

 at least very different from the former. There is, however, a gas 

 relation about which much more is known than about either that 

 of oxygen or of carbon monoxide to haemoglobin, namely, the par- 

 tition of haemoglobin between the two. It would not be unnatural 

 if the relation of affinity of haemoglobin for each of the two gases 

 were affected in the same way by whatever influence affects either 

 the one or the other. That indeed is so of hydrogen-ion concentration. 

 An altered hydrogen-ion concentration affects the affinity of haemo- 

 globin for oxygen, it also affects the affinity of the same substance 

 for CO. The partition coefficient then is not altered. Exposed to a 

 given mixture of oxygen and CO at whatsoever hydrogen-ion con- 

 centration, the oxy- and carboxy haemoglobin will be present in the 

 same proportions. But the cause of the specific differences, whatever 

 it may be, acts differently from hydrogen-ion concentration. That 

 indeed was the essence of the observation of Douglas, Haldane and 

 Haldane on the comparison quoted above of the bloods of man and 

 the mouse respectively. 



Not only does the partition coefficient of the reaction 



COHb -h O2 =^ OaHb + CO 



vary, but the variation seems not to be a function of the affinity of 

 haemoglobin for either of the two gases concerned. 



The reaction equilibrium of the system : oxygen, carbon monoxide, 

 oxyhsemoglobin and carboxyhaemoglobin, may be expressed quanti- 

 tatively in a very simple way. The quotient of the concentration 

 of CO -haemoglobin by that of oxyhaemoglobin bears a constant rela- 

 tion to the quotient of the concentration of CO by that of oxygen 

 (using square brackets to denote "the concentration of") 



[COHb] _ [CO] 

 [O^Hb] ^ [O2] • 



Such a relation may of course be plotted graphically if the value of 

 K is known. For man at 15° C. it is about 540^. 



^ This is the relative concentration of the two gases in the solution which oorre- 

 sponds to a figure of 400 for the relative concentration in the atmosphere above 

 the solution. 



