BIOLOGICAL SIGNIFICANCE OF HEMOGLOBIN 197 



the least possible drop in the pressure at which it leaves. Look then ! 

 with the loss of another 10 mm. pressure the blood curve imparts 

 another 25 per cent, of all its oxygen, the haemoglobin curves 4-6 per 

 cent. 



And we come to the last of the four properties which, at the com- 

 mencement of this chapter, I set forth as giving haemoglobin its great 

 biological significance, namely, its power of buffering a bicarbonate 

 solution and thus of enabhng the body to deal with the production of 

 large quantities of carbonic acid without the COg produced setting up 

 great changes of hydrogen-ion concentration in the blood, and also 

 without its causing so great a rise of COg-pressure in blood as to dam 

 the gas back in the tissues. About this we know more. After a battle 

 as to whether the buffering property of haemoglobin is due to its 

 own power of uniting with carbonic acid or simply to its acting itself 

 as an acid in competition with COg and claiming the bicarbonate, 

 opinion has set itself firmly in favour of the latter view. But the 

 buffering power of haemoglobin is not merely due to its composition ; 

 it is due in part to the fact of its being housed in corpuscles. 

 The red corpuscle and its properties must form the subject of the 

 other volume, and so of this the end. 



