THE UNION OF OXYGEN WITH HEMOGLOBIN 127 



Lastly, if oxygen and carbon monoxide are both present a series 

 of compounds is formed, which are mixed aggregates of the oxy- 

 and carboxyhsemoglobin : 



HbOa + HbCO :i^ Hbg (O^) (CO), etc. 



About the aggregates of the last type it must be admitted that 

 they have never been isolated and further, as far as is known at 

 present, their formation does not affect the spectrum. It has never 

 been claimed that an actual mixture of 50 per cent, oxyhsemoglobin 

 and 50 per cent, carboxyhaemoglobin is spectroscopically different 

 from an optical mixture of the two substances — the former would 

 consist largely of the mixed aggregates from which the latter would 

 be free. 



The equation, which expresses the shape of the dissociation curve 

 on the theory under consideration, is 



^_ Ky[l+b{l-y)]* 

 {l-y){l + ay) 

 X in the above equation is the oxygen pressure expressed in hundredths 

 of an atmosphere, y is the fraction of the total haemoglobin (taken 

 as unity) which is oxyhsemoglobin, K is the equihbrium constant, 

 whilst a and b are constants referring to the degree of aggregation of 

 the oxy- and reduced hasmoglobin respectively. Thus, "the values 

 a = 2, 6 = 8 mean that in fully oxidised haemoglobin | of the oxy- 

 hsemoglobin is aggregated and ^ free, and in completely reduced 

 blood f of the reduced haemoglobin is aggregated and ^ free." 



The theory would probably not be regarded by the authors now 

 as being in nearly as strong a position as when it was pubUshed, for 

 it imphes that the osmotic pressure of a solution of oxyhaemoglobin 

 is greater than one of reduced haemoglobin, which Adair has shown 

 by experiment not to be the case. Both have a molecular weight of 

 68,000. 



L. J. Henderson's theory. Henderson (12), in criticising Hill's theory, 

 took exception to the very large changes in the value of K, pointing 

 out the want of analogy for, say, hundredfold variations in the 

 equilibrium constant of a reaction, wrought by such means as altera- 

 tions in hydrogen-ion concentration (I pass over the impHcation that 

 Hb4 -f 4O2 = Hb408 is the same reaction as Hb + 62= HbOg). 

 Henderson therefore put forward a theory in which the value of 

 the equihbrium constant does not suffer more than a twentyfold 



* In the original paper the dividend is given as Ky [1 —6(1 — y)] — a misprint 

 in the sign. 



