CHAPTER X 



THE DISSOCIATION CURVE OF HEMOGLOBIN 



J- F a hsemoglobin solution be shaken up with oxygen the haemoglobin 

 unites with a definite quantity of the gas, which is in the proportion 

 of 32 grams of oxygen to each 56 grams of iron in the haemoglobin. 

 However much stress we may lay upon this fact — and we cannot 

 lay too much stress upon it — the most elementary consideration of 

 the haemoglobin in the circulation reveals the fact that it is always 

 united with less oxygen than the total amount possible. 



^ A A 



20 



40 



100 



Fig. 19. The numbers denote the pressure of oxygen in mm. 



The next step therefore, if we are to regard oxyhaemoglobin as a 

 chemical compound, is to enquire whether we can reconcile the fact 

 that haemoglobin in the body unites, now with more, now with less 

 oxygen, with the known laws of chemical action. 



The most obvious law which might illuminate this problem is the 

 law of mass action. Our enquiry therefore resolves itself into this : 

 granted a solution which contains (1) oxygen, (2) oxyhaemoglobin, 

 and (3) reduced haemoglobin, does the amount of oxyhaemoglobin 

 depend upon the concentration of oxygen in the solution? The 

 answer to this question can only be supplied by experiment. The 

 experiment is not a difficult one. It is easy to obtain solutions of 

 haemoglobin containing known quantities of oxygen in solution, for 

 the concentration of oxygen in the solution depends directly upon 

 the oxygen pressure of the atmosphere with which the solution is 

 in equilibrium. If a be the volume of oxygen which is dissolved in 



