THE DISSOCIATION CURVE OF HEMOGLOBIN 107 



SO I shall pause for a moment to consider it. Imagine the curve 

 drawn on a sheet of india-rubber, which could be stretched hori- 

 zontally without alteration in its vertical dimensions ; then the altera- 

 tion in the curve which would be caused by rise of temperature 

 could be simulated by mere stretching of the sheet. This relationship 

 is excellently shown in the series of curves given by A. V. Hill and 

 Brown (3) for blood at different temperatures. They are as it were 

 all the same curve but drawn on different horizontal scales. The 

 property is such as would be caused by a simple alteration in the 

 equilibrium constant of the reaction, without any alteration in such 

 factors as are responsible for the degree of inflection of the curves. 

 Therefore we at once get at a conception which separates causes which 

 define the curve into two categories, those which are responsible for 

 the equilibrium constant and for the degree of inflection respectively. 

 A particular factor may affect both the constant and the inflection 

 but it need not necessarily do so and temperature appears to affect 

 the former without altering the latter. The effect of temperature will, 

 however, be treated in greater detail in a future chapter. 



The effect of salts. Concerning the effect of salts on the oxygen dis- 

 sociation curve we know very little. Among the earliest observations 

 made by Camis and myself (4) was the one that certain salts added to a 

 solution of haemoglobin in distilled water altered the curve, making it 

 more inflected. I never know whether it was more fortunate or unfor- 

 tunate that the observation was made at so early a stage ; it was unfor- 

 tunate because at that time the effect of hydrogen-ion concentration 

 was not appreciated and therefore not controlled and it is certain that 

 many of the salts used, e.g. sodium phosphate, altered the hydrogen- 

 ion concentration of the fluid. Moreover, the distilled- water solution 

 was not itself so free from salts as it would have been, had the 

 investigation been made a year later. The fortunate circumstance, 

 however, was that had the discovery not been made at the time it was, 

 it might have been long postponed; for the whole effect of salts on 

 the dissociation curve might have been attributed to changes in 

 hydrogen-ion concentration. In any case the thing must be done 

 again and it wants doing both in relation to the hydrogen-ion con- 

 centration and the haemoglobin concentration. We are only waiting 

 for a certain base line from which to start, in order to test the effect 

 of salts on dilute solutions of haemoglobin. So far as may be gathered 

 from the work on the velocity constants carried out by Hartridge 

 and Roughton (5) salts have no effect on the rate at which really dilute 



