The Intermediate Compound Hypothesis 



Figure 1 . Oxy haemoglobin dis- 

 sociation curve of dilute sheep 

 blood in borate buffer, pVL 9-3, 

 17-19°C, plotted from data of 

 Forbes and Roughton 2 and 

 Forbes 5 . 



100 



eo 



60 



4C 



20 



— ; ~ 



2 4 6 



Qxyyeri Pressure in mm Hg 



particular sample, p0 2 = 3-6 mm at 50 per cent saturation, all the 

 oxygen pressures for the corresponding curve are multiplied by 3-0/3-6 

 before being plotted in Figure 1*). The smooth curve is based not only 

 on the actual points plotted therein (22 out of 25 of these fall within 

 ±1*5 per cent 2 Hb of the curve), but also on numerous other points, 

 which though technically less satisfactory, tally well on the average 

 with the preferred data. Table I shows the relation between p0 2 and y, 

 as read off from the points and the curve of Figure 1 . It is believed 



Table I 



Relation between oxygen pressure, p, and percentage saturation, y, as 



given by data of Forbes and Roughton 2 on oxyhaemoglobin dissociations 



of diluted sheep blood at pH 9-3 



that the values of y are reliable to within ±1-5 per cent saturation 

 over the whole range, and that the accuracy of p ranges from ±'01 

 mm Hg at the lower values of y to ± -03 mm Hg at the higher values. 

 We shall now test the various sets of values of K u K 2 , K 3 , K±, which 

 have appeared in the literature, against the data of Table I. In each 



* This procedure assumes that individual blood variations within the same species only 

 affect the scale of oxygen pressures but not the shape of the dissociation curve. This 

 assumption has been shown to be true within experimental error for the effects of pH and 

 temperature on the dissociation curve (cp Roughton, 1936), but, as stressed in that paper, 

 there is no proof that the assumption is mathematically exact. 



85 



