164 HEMOGLOBIN 



of blood in 5000 of buffered water. The difficulty is that in order to 

 make the reaction progress in the one direction either or both of 

 the Hb and the CO should be removed as it is formed. The substances 

 tried for the purpose of removing reduced haemoglobin were oxygen 

 and potassium ferricyanide. The use of oxygen depends for its justifi- 

 cation on the assumption that when HbCO in the presence of oxygen 

 forms Hb02 the reaction consists of two separate stages: 



HbCO — »► Hb + CO, 

 Hb + Oa-^-HbOa, 

 and not one stage 



HbCO + 02^ HbOg + CO. 



Now we shall treat of this reaction in the next chapter, but here 

 we would say that neither view of the nature of the change from 

 carboxy- to oxyhsemoglobin can be regarded as definitely proven. 

 For the view just stated there are" several pieces of evidence. Those 

 relevant here are (1) that Hartridge and Roughton did not find in- 

 creasing the concentration of oxygen appreciably increased the velocity 

 of the decomposition of COHb, and (2) that the maximum rate of dis- 

 sociation of Hb with CO in the presence of ferricyanide is approxi- 

 mately the same as in the presence of oxygen. The uncertainty of 

 the position prevents us, at present, from adopting any definite 

 coefficient for the dissociation velocity of carboxyhaemoglobin, but it 

 does not obscure the important issue, namely, that the velocity 

 constant is an extremely small one. The breakdown takes place very 

 slowly. Where oxyhsemoglobin would dissociate in a fraction of a 

 second, carboxyhaemoglobin requires minutes, and of these more than 

 one or two. This is so where oxygen is used as a haemoglobin acceptor. 

 If the use of the oxygen is unjustifiable the reason would be that 

 the oxygen hustled the carbon monoxide out of the haemoglobin, and 

 the conclusion would be that in the absence of the oxygen the break- 

 down of the haemoglobin would be even more leisurely. 



Summing up then, if we select conditions of temperature and 

 hydrogen-ion concentration such as are found in the body, we may 

 imagine a certain degree of union of haemoglobin with oxygen as 

 taking place in one-thousandth of a second ; the same degree of union 

 of carbon monoxide with haemoglobin would take one-hundredth of 

 a second or more. The reverse process in the case of the oxyhsemo- 

 globin would take one-twentieth of a second, and in the case of 

 the CO-haemoglobin over 3 minutes. The range of Hartridge and 



