HALDANE EFF'^CT 273 



of pressure. If m is the degree of saturation of the pigment with 

 carbon monoxide at a pco of q, the combination of the remainder of 

 the pigment with oxygen will trace out the path taken by the disso- 

 ciation curve as y increases from m to /. This curve is no longer of 

 the original sigmoid shape, and the dissociation of the oxyhemoglobin 

 for a given drop of partial pressure is less than that which would have 

 taken place in the absence of carbon monoxide. It is possible to 

 predict the saturation of the pigment if both the gases are present 

 from a knowledge of the dissociation curve for one of them as well 

 as of the value of the partition coefficient, K. Roughton and Darling 

 (2366) point out that this would be expected on Pauling's theory only 

 if the interaction constant a is the same for the combination of 

 oxygen and carbon monoxide with hemoglobin. 



The latter workers (532) also showed that the dissociation of 

 oxygen from oxyhemoglobin was affected by the presence of hemi- 

 globin in the same way as it was affected by carbon monoxide. They 

 failed to find significant differences, however, between the dis.sociation 

 curves of oxyhemoglobin-hemfglobin mixtures prepared by the oxida- 

 tion of a certain fraction of the hemoglobin by nitrite or by ferri- 

 cyanide or prepared by addition to oxyhemoglobin of a solution of 

 hemoglobin. In the former case, intermediates containing both 

 ferrous and ferric iron would be expected to be present, while in the 

 latter, the solution would be expected to contain initially only mole- 

 cules containing four ferrous or four ferric iron atoms, in which case 

 the dissociation of the oxyhemoglobin should be uninfluenced by the 

 hemoglobin. In explanation of this negative finding they suggested 

 that equilibrium was established relatively rapidly between molecules 

 containing only ferrous, or only ferric, iron atoms, and molecules 

 containing both : 



where the first square represents a molecule of hem/globin. 



Drabkin and co-workers (623) have recently attempted to differ- 

 entiate physiologically between the effects produced by the presence 

 in the blood of dogs of hybrid hemoglobin molecules containing both 

 oxygen and carbon monoxide, and the effects produced by an equiva- 

 lent mixture of hemoglobin molecules, each of which was homogeneous 

 with respect to the gas with which it was combined. They were 



