THE NATURE OF HEMOGLOBIN SOLUTION 81 



So much for the technical difficulties, great enough, but less than 

 those imposed by the nature of haemoglobin itself. 



What if haemoglobin has no osmotic pressure, the pressure which 

 is set up being due to adherent salts? In such an event haemoglobin 

 would not be in solution ; but in such a case also the particular con- 

 ditions which Adair demanded (8) would probably not have been 

 complied with. They were (1) that successive samples of haemoglobin 

 should give the same value iinder similar conditions; (2) that if, 

 when final equilibrium had been reached, the pressure were disturbed 

 in either direction, it should return to the previous value; and 

 (3) that the pressure should be maintained at a constant level for 

 a considerable time. Haemoglobin gave results which fell so well 

 within the set limitations, as to leave no doubt that it did of itself 

 exert a definite osmotic pressure. 



Definite ! Yes, but the osmotic pressure was a function of the 

 conditions under which it was measured, as indeed Roaf has dis- 

 covered. How could this be? The idea which underlay Hiifner's 

 work and, as I suppose, Waymouth Ri,eid'Sj was that the haemoglobin 

 molecule was just a molecule — as it might be urea or sugar but vastly 

 larger. How much larger, was what they set themselves to discover. 

 The modern view is different, it is that haemoglobin is something 

 which in alkaline solutions behaves like an acid uniting with a base 

 and in acid solutions behaves like an alkah, uniting with an acid. 

 Picture it then in a dilute solution of sodium hydrate, forming a salt — 

 sodium haemoglobinate ; the precise number of gram atomic weights of 

 sodium with which each 17,000 gram units of haemoglobin unites 

 need not be discussed here, but it may be quite considerable, say 

 ten, if the solution is sufficiently alkaline. A true salt is formed, that 

 is to say the sodium atoms are at least partially in the ionised con- 

 dition as also is the haemoglobin. The osmotic pressure of course 

 will depend upon the number of ions. Within limits the more alkaline 

 the solution the greater will be the osmotic pressure of the sodium 

 haemoglobinate. Hence in an alkaline solution the osmotic pressure 

 will fall as the alkalinity diminishes. The same is true of an acid 

 solution where the haemoglobin acts as a base and attaches to itself 

 numerous acid ions, the less the concentration of hydrogen ions the 

 less the osmotic pressure caused by the haemoglobin. At the isoelectric 

 point therefore of the haemoglobin (about pH. 6-8) the haemoglobin 

 should on this theory exert its minimum osmotic pressure (9). It is 

 not very easy to obtain haemoglobin quite free from base and at 



