THE DISSOCIATION CURVE OF HEMOGLOBIN 111 



the inflection became relatively constant, the CO2 affecting the curves 

 much in the way that temperature might do. 



Thus the first effect, when CO2 is added to a salt-free or nearly 

 salt-free solution of haemoglobin, includes a salt effect. Herein haemo- 

 globin differs from blood. CO2 has no effect or almost no effect on 

 the degree of inflection of the oxygen dissociation curve of blood, the 

 inflection is already present even in the COa-free blood, being ap- 

 parently produced and stabilised by the salts ; the effect of concentra- 

 tion we do not yet know. The curves published by Bohr, Hasselbalch 



100 



20 40 60 80 



Fig. 34. Oxygen dissociation curves at different H-ion concentrations. 

 y = percentage of oxygenation. 

 X = oxygen pressure in mm. 



and Krogh(iO) and Barcroft and Poulton(ii), as well as by Douglas, 

 Haldane and Haldane(i2), illustrating the effect of COg on blood 

 exposed to CO in the absence of oxygen, all agree in showing that 

 there is very little difference in the degree of inflection of the curves 

 at various CO2 pressures. The curve for any one CO2 pressure, for 

 blood, could be almost superposed on that for any other pressure 

 by merely altering the horizontal scale on which it is drawn. 



The degree to which the curves (at varying CO2 pressures) are 

 unaltered in inflection may be shown by a comparison of Figs. 35 



