CHAPTER II 



THE DISSOCIATION CURVE OF HAEMOGLOBIN 



IF a haemoglobin solution be shaken up with oxygen, the haemo- 

 globin 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 con- 

 sideration of the haemoglobin in the circulation reveals the fact 

 that it is always united with less oxygen than the total amount 

 possible, frequently with much less and in any case with no precise 

 or invariable amount. 



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

 chemical compound, is to inquire 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 inquiry 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 concentrations of oxygen in solution, 

 for the concentration of oxygen 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 1 c.c. of the 

 solution at the temperature of the experiment and at 760 mm. 

 pressure, then the concentration of oxygen at any other pressure 



p is p j: . The experiment then will consist of exposing portions 

 of a haemoglobin solution to various atmospheres containing known 



