76 



HEMOGLOBIN 



critical pressure at above which all the haemoglobin would be oxy- 

 haemoglobin and below which it would be reduced haemoglobin. 



In the case of haemoglobin it is particularly desirable to have 

 clear views as to whether it really is in solution or not, because the 

 whole modern theory of haemoglobin which contemplates the sub- 

 stance as one which presents the properties of an acid and a base in 

 varying degrees under different circumstances, assumes fundamentally 

 that the substance is in solution, otherwise it would not dissociate 

 into hydrogen, hydroxyl and haemoglobin ions. 



12 3 4 5 6 



8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 



FiQ. 14. Dissociation curves of oxyhaemoglobin, all 50 per cent, saturated at 10 mm. 

 pressure, but with varying values of n. 



Another criterion which is sometimes cited of whether a substance 

 is or is not in solution is its power to exert an osmotic pressure. 

 What justification had we a while back for stating that haemoglobin 

 possessed this property? The answer cannot be given Avithout going 

 in some detail into a rather chequered chapter of physiological 

 research. The importance of the issues involved was recognised by 



