128 HEMOGLOBIN 



variation — a conception which appears to be true of dilute solutions 

 according to the kinetic evidence. There is no corresponding kinetic 

 evidence with regard to strong solutions. 



Henderson started from the fact that if the solution be acidified the 

 haemoglobin unites less readily with oxygen, while if the solution be 

 rendered more alkaline the haemoglobin unites more readily with 

 oxygen. Now the addition of oxygen to reduced haemoglobin makes 

 the solution more acid, and at first sight one might therefore expect the 

 haemoglobin to lose its grip of its oxygen but, according to Henderson, 

 there is a difference between increasing the hydrogen-ion concentra- 

 tion of a haemoglobin solution by the addition of acid and increasing 

 it by the addition of oxygen. The former makes the haemoglobin 

 solution unite with less base, the latter makes the haemoglobin unite 

 with more base. Therefore — so runs the argument as I understand it — 

 the addition of oxygen to haemoglobin, while it renders the solution 

 more acid, makes the haemoglobin behave in the same way as would 

 the addition of alkah to the solution: that is, it causes the haemo- 

 globin to unite more readily with oxygen and thus changes what 

 would have been a hyperbohc into an inflected curve. 

 I think Henderson's theory really amounts to this : 

 (a) That in any haemoglobin solution there exist the following 

 substances which I shall for the moment call by names that will 

 indicate their compositions : 



(1) Haemoglobinic acid. 



(2) Sodium haemoglobinate. 



(3) Oxyhaemoglobinic acid. 



(4) Sodium oxyhaemoglobinate. 



(6) That therefore from the point of view of the oxygen there are 

 two equilibria: 



(1) H.Hb + Oa^^H.HbOg. 



(2) Na.Hb+ Oa^S^^Na.HbOa. 



(c) That the quantity of sodium haemoglobinate increases gradually 

 as the haemoglobin acquires oxygen. 



(d) That the sodium haemoglobinate system has a much stronger 

 affinity for oxygen than the haemoglobinic acid system. The final 

 dissociation curve is a composite of the dissociation curves of the 

 two systems. 



This theory has much that is attractive. It is capable of being 

 elaborated by making various assumptions, and I have little doubt 



