HEMOGLOBIN, CARBON MONOXIDE AND OXYGEN 169 



factor, namely, light, to which the reaction is very sensitive. Light 

 tends to expel the CO from haemoglobin to the advantage of the 

 oxygen. If, therefore, the equilibrium between oxygen and haemo- 

 globin and CO is struck in the light, there will be a less percentage of 

 CO-hsemoglobin and a greater percentage of oxyhaemoglobin, than 

 if the equiUbrium is struck in the dark. So far as I know no systematic 

 work has been pubHshed on this subject, in the sense that the quanti- 

 tative relation of the value of K to the measured intensity of light has 

 never been determined even for any specified wave length; but the 

 general effect has been observed by many who have worked upon 

 the subject — Haldane in the first instance and later Hartridge and 

 others. The subject will be more fully discussed in a later chapter. 



In the above discussion of the reaction of haemoglobin with oxygen 

 and carbon monoxide simultaneously it has been assumed tacitly 

 that sufficient of the two gases taken together has been available 

 for the saturation of the haemoglobin with either the one or the other, 

 that is to say that no appreciable amoimt of reduced haemoglobin 

 is present. The consideration of the system, Hb, HbOg, HbCO, O2 

 and CO, all present simultaneously, forms a very interesting problem 

 and one on which Httle work has been done. 



The following avenue of approach might seem to be a rather natural 

 view of the subject, and one which has been used by Douglas, Haldane 

 and Haldane (2) and A. V. Hill (6). 



Consider first the quantity of reduced haemoglobin in the system ; 

 a curve may be drawn indicating the quantity of haemoglobin which 

 is not combined with gas, from that which is. The gas pressure may 

 be expressed in equivalents of oxygen pressure; reverting to the 

 example given on page 166, one part of CO would count as 310 

 equivalents of oxygen. So that a mixture of -01 mm. of CO and 

 5 mm. of O2 would count as 



CO = -01 X 310- 3-1 

 O2 = 5 = 5_ 



8*1 virtual mm. Og. 



The dissociation curve then between gas-free and gas-combined haemo- 

 globin would be the ordinary one of oxyhaemoglobin, but in which 

 mm. Oa-pressure was replaced by virtual mm. Og-pressure. 



The partition of the gas-combined haemoglobin would then take 

 place just as if the reduced haemoglobin were not present. To carry 

 the examples given above a Httle further. 



