126 HEMOGLOBIN 



which has the same pressure at 50 per cent, saturation. Such a 

 curve might easily obey Hill's equation with a variation in the value 

 of n, but the matter has not been put to any exhaustive test. 



Since Hill's theory was propounded the atmosphere surroimding 

 haemoglobin has changed. Adair (lO) and Svedberg(ii) have inde- 

 pendently arrived at the conclusion that the molecular weight of 

 haemoglobin is at its simplest (16,700)4, i.e. w = 4, and in the case of 

 the latter research it was clear that 4 is not an average figure but is 

 the actual value for each molecule. Therefore, if Hill's theory was held 

 now, it would resolve itself into a statement that the basic equation 

 was 



y _ Kx* 

 Too" 1 + Kx^' 



In so far as this equation does not fit actual curves (and it fits no 

 actual curve determined experimentally) some reason must be shown 

 for the introduction of a correction. This point has been discussed 

 by Adair and will be considered as part of his theory. 



Douglas, Haldane and Haldane's{9) theory is based on Hill's idea 

 of aggregation, but it introduces another compHcation, namely, that 

 each time the haemoglobin aggregate unites with oxygen it breaks up 

 into simple molecules and each of these, having taken up its load of 

 oxygen, re-aggregates. 



Moreover, the oxyhaemoglobin and the reduced haemoglobin do not 

 aggregate to the same extent. The tendency of the reduced haemo- 

 globin to aggregate is greater than that of the oxyhaemoglobin. There 

 are therefore several reactions taking place at the same time and all 

 obeying the law of mass action : 



Hb -F Hb 5^ Hba, 

 Hbg-f Hb:^Hb3, 

 Hb3 + Hb:i^Hb4,etc.; 

 also 



HbOa + HbOai^HbaO^, 

 HbOa + Hb204 z^ HbgOe , 

 HbOa + HbgOfi :i^ Hb408 , etc. ; 



as well as the reaction of haemoglobin with oxygen, which can only 

 take place as the result of the disruption of these units. 



Precisely analogous is the reaction of haemoglobin with carbon 

 monoxide; the reduced haemoglobin and the carboxyhaemoglobin 

 respectively aggregate — the latter more readily than the former. 



