Tlte dissociation curve of haemoglobin 17 



We are impelled to ask whether any definite relationship exists 

 between these quantities of oxyhaemoglobin and the oxygen pressures 

 to which they correspond. In doing so we must bear in mind that 

 we shall shortly be face to face with a very serious position, for the 

 very relationship which we are about to investigate is defined by 

 the law of mass action itself, and should the relation as found not 

 agree with that as prescribed, our theory must be abandoned and 

 some other explanation of the properties of haemoglobin must be 

 found. Let us introduce the element of pressure quantitatively by 

 spacing the cylinders apart from one another at distances which are 

 proportional to the concentrations (or pressures) of oxygen dissolved 

 in the solution, as is done in Fig. 6. 



By joining the points which divide the blue and red portions of 

 the cylinders we obtain a curve which relates (1) the percentage of 

 the total haemoglobin which is oxyhaemoglobin to (2) the concentra- 

 tion of oxygen dissolved in the fluid at all concentrations of oxygen 

 between and '0029 c.c., and consequently to all pressures of oxygen 

 between and 100 mm. This curve representing the equilibrium 

 between oxygen and haemoglobin is called the dissociation curve of 

 oxyhaemoglobin. It is shown in Fig. 7. 



Let us now turn from the observed properties of haemoglobin to 

 the other side of the question, namely the requirements of the law of 

 mass action. This law has been stated quantitatively by Guldberg 

 and Waage in the following terms : 



" The velocity of chemical change is proportional to the product of 

 the active masses of the reacting substances." The chemical change 

 is conceived of as taking place in both directions simultaneously, 

 that is to say, oxyhaemoglobin is all the time being formed and 

 being broken up, and we therefore have these two changes taking- 

 place at the same time, (1) the formation, (2) the breakdown 

 of oxyhaemoglobin. Since these changes balance one another, the 

 whole system being in equilibrium, the velocities of the two changes 

 are equal. Taking first the formation of oxyhaemoglobin, the re- 

 acting substances are reduced haemoglobin and oxygen and the 

 velocity of their reaction is proportional, says the law, to the product 

 of their concentrations in the solution. If C be the concentration 

 of oxygen and C R of reduced haemoglobin, then the velocity of the 

 reaction is proportional to, or is equal to, a constant k multiplied by 

 the product of C R and C , i.e. k (C R x C ). As regards the other 

 phase of the reaction the breakdown of oxyhaemoglobin there 



B. R. F. 



