RESPIRATION 8l 



On this view the aggregated haemoglobin molecules have their 

 molecular affinities saturated, and therefore go out of the re- 

 action between oxygen or CO and haemoglobin, thus following 

 the general principle that corpora non agunt nisi soluta. The only 

 reaction taking place between the haemoglobin and oxygen is thus 

 the first one mentioned above. To explain the actual form of the 

 dissociation curve for blood or salt solutions we assumed that the 

 degree of aggregation depends on the concentration of the haemo- 

 globin or oxyhaemoglobin in the solution, in accordance with the 

 reactions 



Hb + Hb^Hbs 

 Hb + Hbs^Hbg etc. 

 HbOs + Hb02^Hb204 

 HbOg + HbsO^^HbgOe etc. 



Thus reduced haemoglobin and oxyhaemoglobin molecules ag- 

 gregate separately; and if we assume that reduced haemoglobin 

 aggregates more readily than oxyhaemoglobin we can explain at 

 once the distortion of the curve from the primary rectangular 

 hyperbola obtained by Barcroft. For as the oxyhaemoglobin be- 

 comes reduced the aggregation of the reduced haemoglobin mole- 

 . cules must increase more rapidly than the aggregation of the 

 I oxyhaemoglobin diminishes. Hence at what would, but for the 

 I aggregation, be half-saturation, there are fewer free reduced 

 '! haemoglobin molecules and more free oxyhaemoglobin molecules 

 than would be the case if the oxyhaemoglobin molecules aggre- 

 gated as readily as the reduced haemoglobin molecules. Hence 

 the actual saturation will be much less than half, and not just half, 

 as would be the case if the tendency to aggregation were the same 

 for the two kinds of molecules. The actual dissociation curve will 

 also have the double bend which is characteristic of it. We also 

 assumed that the saturated molecules of HbCO have just as much 

 tendency to aggregate with one another and with the saturated 

 . molecules of HbOg as have the molecules of HbOa- For this reason 

 the dissociation curve of HbCO in blood in presence of oxygen 

 must be a rectangular hyperbola, as is actually the case, though its 

 dissociation curve in the absence of oxygen has the same form as 

 the dissociation curve of HbOs- 



By making certain assumptions (for a statement of which I 



i must refer to our original paper) J. B. S. Haldane found that the 



|, following equation to the curve for human blood in Figure 20 



