162 HAEMOGLOBIN 



has been given in the last chapter, and is briefly that oxygen or 

 ferricyanide can be used as acceptors of the haemoglobin without 

 retarding the rate at which the HbCO is broken down, 



II, So much for the conversion of carboxyhsemoglobin into oxy- 

 haemoglobin ; now as regards the opposite phase, the conversion of 

 the oxy- into the carboxy-compound. Here again, if there are two 

 stages in the reaction : 



(a) HbOa ^^02+ Hb, 

 (6) Hb + CO — HbCO, 



the first is much more rapid than the second, though the disparity 

 is not so great as in the previous case, so that here also the oxygen 

 and the reduced haemoglobin are practically in equilibrium, and the 

 rate at which the whole process proceeds is governed principally by 

 the rate at which reduced haemoglobin unites with carbon monoxide ; 

 nevertheless it is to some extent influenced by the rate at which the 

 haemoglobin is hberated. Now if the reaction were 



HbOg + CO -^ HbCO + O2 



the velocity in that direction would be influenced only by the reacting 

 masses of the HbOg and CO and not at all by the active masses of 

 the O2 or of the HbCO, Of course as these last accumulate they 

 would set up a reaction in the opposite direction, but that is another 

 matter. 



Now, in practice, the velocity of the reaction in the direction from 

 HbOa to HbCO does depend on the reacting mass of oxygen, and this 

 is intelligible on the two-stage theory, for the increase in the reacting 

 mass of oxygen, by pushing the reaction (a) in the direction 



HbOa ^-02+ Hb, 



will decrease the concentration of Hb at any given time and therefore 

 decrease the active mass of Hb available for the reaction (6), 



So much for the evidence in favour of the two-stage reaction : now 

 as to the difficulties regarding it. 



As a preUminary it may be useful to tabulate the effects of in- 

 creased hydrogen-ion concentration and temperature on the principal 

 reactions which have been considered. (See table on p. 163,) 



Now if the conversion from oxy- to carboxyhaemoglobin is in two 

 stages, following equations (2) and (3) in the table below, the effects 

 of temperature and pH should be the products of the individual 

 coefficients, i.e, a rise of 10° C. should accelerate the reaction 



