CHAPTER XII 



THEORIES OF THE UNION OF OXYGEN WITH 

 HAEMOGLOBIN 



X o say that every worker on haemoglobin has had a pet theory of 

 the way in which that substance unites with oxygen would of course 

 be a gross exaggeration, nevertheless the lure of this subject has been 

 remarkable — perhaps "remarkable" is the wrong word because the 

 importance of the subject is so great. After all, biologically, the re- 

 action is one upon which much of Ufe depends and, biochemically, 

 there is much to be learned about proteins in general from a complete 

 understanding of haemoglobin. Let us say that the lure of the subject 

 has been "more than considerable." 



When The Respiratory Function of the Blood was first written, interest 

 centred largely about the question of whether the union of oxygen 

 with haemoglobin was a chemical or a physical one. Of the seven 

 theories that come to the mind six are chemical and one is physical. 

 In so far as there is any real difference between a chemical and 

 physical conception, there seems to be no doubt that oxyhaemoglobin 

 is a true chemical compoimd. 



At the risk perhaps of some repetition let us state the case for and 

 against the adsorption hypothesis. This theory was put forward by 

 Wolfgang Ostwald(i) at a time when the idea of adsorption was very 

 much in th^ air. The imderlying conception was that the large haemo- 

 globin molecule attracted oxygen molecules to it which remained 

 adherent to the surface in view of their electrical charges. It assumed 

 that the haemoglobin molecule was something large enough to have 

 a surface with definite properties as opposed to those of the rest of 

 the molecule, and that the quantity of oxygen which adhered to the 

 surface at any given time depended upon the pressure of oxygen 

 present and could be increased indefinitely by increasing the oxygen 

 pressure. Of course it is not suggested that equal increments of 

 pressure produce equal increments in the quantity of adsorbed oxygen. 

 The relation is a parabohc one. 



The actual facts are in conflict with the above statement of theory 

 at several points, brief and crude as that statement may be. 



In the first place the relation between haemoglobin and oxygen 



