140 HEMOGLOBIN 



accumulating oxyhaemoglobin must be allowed for by calculation. This 

 allowance can be made if the velocity constant for the reaction, 



HbOa -»- Hb+ O2, 

 be known. 



The question may be asked with reason: Does not just the same 

 argument apply to the reaction, 



HbOg-^ Hb + O2, 



as to the oxidation ? Is it possible to find the velocity constant for 

 the reduction of haemoglobin without a knowledge of that for the 

 oxidation? And indeed the argument would appear to have great 

 force inasmuch as the velocity constant for the oxidation is much 

 greater than for the reduction. The answer is that Hartridge and 

 Roughton have broken this vicious circle in the following way (5). 

 They have succeeded, in the case of the reduction, in removing the 

 oxygen from the sphere of action as quickly as it is formed ; this they 

 achieved by the presence in the system of the reducing agent, 

 sodium hydrosulphite — ^Na2S2 04. 



Let us turn to the consideration of Hartridge and Roughton's experi- 

 ments for the measurement of the velocity constant for the reaction 



HbOa— ^ Hb+ O2. 



The apparatus was essentially the same in nature as that which 

 we have already described, but inasmuch as the reaction is slower, 

 the whole apparatus does not require to be so powerful. A slower 

 current along the observation tube suffices, powerful pumps for the 

 propulsion of the fluids are unnecessary, and the pressures inside the 

 apparatus are not so great but that it can be assembled from ordinary 

 laboratory materials. The reacting fluids led into the observation 

 tube were, fluid I, a solution of oxyhaemoglobin, which necessarily 

 contained dissolved oxygen and which was buffered to the required 

 hydrogen-ion concentration; fluid II, a solution of hydrosulphite, 

 which in the nature of the case was free from dissolved oxygen — any 

 such would at once be taken up by the hydrosulphite. 



When the fluids met, the following sequence of events took place. 

 Firstly, the hydrosulphite ate up the oxygen in solution. Secondly, 

 when the oxygen pressure in the fluid was reduced to a few milli- 

 metres (the temperature being 15'6° C.) the oxyhaemoglobin com- 

 menced to yield its oxygen, which for a moment went into physical 

 solution. Thirdly, this oxygen was immediately laid hold upon by the 



