Effect of acid on aggregation 59 



and Halclane by the curves which they obtained for the dissociation of 

 carboxyhaemoglobin into reduced haemoglobin and CO, in the presence 

 of different CO 2 pressures. Clearly they approximate to this ideal. 



It seemed desirable to redetermine the corresponding points for 

 oxyhaemoglobin for the purpose of ascertaining whether there were 

 any difference between the curves at various CO 2 pressures other 

 than the scale on which they were drawn. To this matter Poulton 

 and I addressed ourselves. We made determinations of points on 

 the dissociation curve in the presence of 3, 20 and 90 mm. C0 2 

 respectively. These points are shown in Fig. 30. The curves in this 

 figure are all derived from my dissociation curve at 40 mm. pressure. 

 For any percentage saturation the pressure on the line corresponding 

 to 3 mm. C0 2 line is ^, that on the 20 mm. line is ^, and on the 

 90 mm. line is f of the pressure on my 40 mm. line. 



Not until Poulton and I arrived at 90 mm. C0 2 was there any 

 suggestion of a discrepancy. The discrepancy that occurred then 

 may be due to experimental error, for the determinations could just 

 be included within the extreme limits of such errors. Nevertheless 

 in view of the fact that there is a similar disposition of the points 

 on the corresponding curve for CO haemoglobin (Fig. 29), and also 

 that a similar tendency is evident in some of the curves obtained 

 on Monte Rosa, I am inclined to think that at C0 2 pressures of 

 about 100 mm. the dissociation curve does become slightly more 

 curved than it would be were it a mere horizontal expansion of the 

 curves obtained at lower pressures *. 



This slight divergence at a very high concentration of CO 2 does 

 not seem to invalidate the general truth of the conception that the 

 main action of increased hydrogen ion concentration is to reduce 

 the effective concentration of oxygen in precisely the way we have 

 described. One of the most unbending of physical laws (Boyle's law ) 

 bends when pushed to extremes. The laws of ionic dissociation do the 

 same, and it could scarcely be expected that our present case should 

 be more rigid than these. The important point is that over ranges 

 of CO 2 pressure which are not extreme the curves appear to differ 

 merely in the scale on which they are drawn. This, as I have indi- 

 cated, suggests that in the presence of considerable quantities of salt 

 small changes in hydrogen ion concentration do not appreciably alter 

 the degree of aggregation of the molecules. 



Now that I have stated the main facts about the relation of salts 



* See Appendix II. 



