CARBON MONOXIDE— REDUCED HEMOGLOBIN 155 



Houghton's work therefore extends to the measurement of velocity 

 coefficients of reactions, one of which is something hke two hundred 

 thousand times as rapid as the other. 



A moment ago I alluded to conditions of temperature and of 

 hydrogen-ion concentration. Reference to Chapter xi will show that 

 the reaction 



Hb + O2 — ^ HbOa 



is but slightly affected either by hydrogen-ion concentration or by 

 temperature, but that the reaction 



HbOg -^ Hb -h O2 



is extremely sensitive to temperature, and over a certain range of 

 alkalinity to changes in hydrogen-ion concentration. That range is 

 very near the neutral point. 



We may ask ourselves : Do these corresponding reactions of haemo- 

 globin with CO show the same properties? We can speak more 

 confidently about the union of CO and haemoglobin than about the 

 opposite phase of the reaction. Is it, like that of haemoglobin with 

 oxygen, independent of temperature and hydrogen-ion concentra- 

 tion? The answer is that both hydrogen-ion concentration and tem- 

 perature have an influence on the rate of association of carbon 

 monoxide with haemoglobin, though the influence is not a very great 

 one. Thus the rate of association increases with the alkalinity of the 

 fluid, being about half as great again at ^H == 10 as at pH = 6. 

 Rise of temperature also increases the rate of association of carbon 

 monoxide with haemoglobin; the velocity constant of the reaction 

 varies from 1-4 to 2 according to the specimen of haemoglobin studied. 



Here therefore are two quahtative differences between the be- 

 haviour of haemoglobin towards carbon monoxide and its behaviour 

 towards oxygen. The other important quahtative difference is that 

 light dissociates carboxy haemoglobin and not oxy haemoglobin. 



Turning to the dissociation phase of the reaction, it will be recalled 

 that the dissociation of oxyhaemoglobin into reduced haemoglobin 

 and oxygen has a very high temperature coefficient — in sheep's blood 

 the velocity constant increases about fourfold for a rise of tempera- 

 ture of ten degrees. In the few cases so far observed the temperature 

 coefficient of the dissociation of carboxyhaemoglobin varied between 

 3 and 6. We have already seen that the velocity of combination of 

 CO with haemoglobin is scarcely affected by changes in hydrogen-ion 

 concentration. There is a field left for investigation as to why, when 



