68 Chapter V 



CO-haemoglobin curves. It is so chosen that the middle point of the 

 CO curve (Fig. 35, .4) at 42 mm. C0 2 pressure coincides on paper with 

 the middle point for the corresponding curve of oxyhaemoglobin. 

 I then tested whether curves drawn from Hill's equation 



fitted the points, with the result which may be seen in Fig. 35. Not 

 only do the lines fit the points absolutely in the case of each of the 

 four curves given, but as in the case of oxyhaemoglobin the lines are 

 all obtained with the same constant value of n, 2*5, and with a change 

 merely in the value of K. The 42 mm. C0 2 curve therefore not only 

 coincides with the similar curve for oxyhaemoglobin at the point of 

 50 per cent, saturation, but is the same identical curve with the same 

 value for n. The identity does not stop here, for the curves for other 

 C0 2 pressures are identical in Figs. 34 and 35. In fact Fig. 35 is the 

 exact counterpart of Fig. 34 but for the trifling difference caused by 

 the disparity between Douglas' blood and my own. 



The aggregation hypothesis forms a complete explanation of the 

 facts that are known concerning the reactions 



Hb + 2 ^= Hb0 2 

 and Hb + CO ^ HbCO. 



The more complicated case remains for consideration that of 

 the reaction 



Hb0 2 + CO ^ HbCO + O 2 . 



There are several remarkable facts about this reaction, any one of 

 which might prove upsetting to a general theoretical explanation. 



(1) The reaction, unlike those which we have discussed, is repre- 

 sented by a rectangular hyperbola. 



(2) This hyperbola, unlike the curves of haemoglobin in the 

 presence of oxygen, or of CO separately, is almost unaffected by 

 acids and by salts. 



(3) While the curve of the reaction 



Hb0 2 + CO 5^ HbCO + O 2 



is a rectangular hyperbola in the presence of an ample supply of 

 O 2 and CO, it ceases to be so when there is insufficient CO and O 2 

 present to saturate the Hb, i.e. when there is a considerable quantity 

 of reduced haemoglobin present. Under these circumstances the 

 entire form of the curve changes in the way which is shown in 

 Fig. 36< u >. 



