150 HEMOGLOBIN 



CO is in equilibrium with a certain percentage of COHb in a certain 

 blood then, under similar circumstances, in another sample of the 

 same blood 245 times that pressure of Og will be in equilibrium with 

 the same percentage of oxy haemoglobin. This statement may be 

 made within limits which are extraordinarily narrow considering that 

 the oxygen curves were done with the old pump and that indeed 

 the curves were extrapolations, i.e. they were contours drawn on 

 what was virtually a surface which represented three variables, the 

 oxygen pressure, the COg-pressure and the percentage saturation. 

 While in general the curves given by Douglas, Haldane and Haldane, 

 and those given by Bohr, Hasselbalch and Krogh, are superposable, 

 there is a certain slight systematic difference which might be passed 

 over, but for the fact that it raises a point of theoretical interest. 

 If any pair of corresponding curves be selected, say those at 80 mm. 

 COg-pressure, the oxyhsemoglobin curve tends to cross the CO-haemo- 

 globin curve, being to the left of it at low percentage saturations 

 and to the right of it at high percentage saturations. Now it must be 

 remembered that oxyhaemoglobin is a stronger acid than reduced 

 haemoglobin and therefore, as the oxygen leaves the corpuscle, the 

 reaction of the inside of the corpuscle becomes more alkaUne, which 

 fact would tend to divert the curve to the left. So one may pause a 

 moment to enquire whether the same is true of carbon monoxide. 

 If the carboxyhaemoglobin is not a stronger acid than reduced haemo- 

 globin we have a qualitative difference between the relationship of 

 oxygen and carbon monoxide to haemoglobin. This difference, if it 

 existed, might account for the crossing of the curves. 



The evidence, however, is in quite the opposite direction. Parsons (3> 

 (using the hydrogen electrode) and the Rockefeller school (4) agree that 

 carbon monoxide produces much the same change of hydrogen-ion 

 concentration in reduced blood as oxygen would do. And on general 

 grounds this is likely to be so, for the change of hydrogen-ion concen- 

 tration wrought by oxygen or CO on blood is but the counterpart 

 of the change of oxygen (or CO-) content wrought by alteration of 

 the hydrogen-ion concentration. There is reason to beUeve that 

 the very alterations in 02-content and CO-content, which correspond 

 so exactly in Fig. 47, are due to changes in hydrogen-ion content 

 and not to specific changes in COg . It is hkely that saturation, whether 

 with oxygen or CO, will produce the same effect on the hydrogen-ion 

 concentration. 



If, therefore, we wish to discover the reason why the curves of 



