READJUSTMENTS OF REGULATION 31 



otherwise needed. Excess of C0 2 , on the other hand, 

 facilitates the dissociation, so that the giving off of 

 C0 2 to the blood in the body capillaries helps to make 

 the curve steeper and so facilitates the oxygen supply 

 to the tissues. 



The curve is not at all of the shape which would be 

 expected on purely chemical grounds from what is 

 known of other substances which dissociate in a similar 

 manner. It was discovered by Barcroft and his pupils 

 that the inorganic salts present along with the haemo- 

 globin in the red corpuscles determine this peculiar 

 form. When the haemoglobin is freed from these 

 salts its dissociation curve has the form which would 

 have been expected on chemical grounds — namely, that 

 of a rectangular hyperbola. With this form of curve 

 the oxyhaemoglobin would be wholly unsuited for 

 performing the work which it actually performs in 

 the body. The action of the salts is almost certainly 

 connected with their power of causing the haemoglo- 

 bin molecules to become aggregated into groups. Bar- 

 croft also found that it is in virtue of its action as 

 an acid when in solution that C0 2 affects the dissocia- 

 tion curve. Alkalies shift the curve to the left, while 

 acids shift it to the right; and the changing position 

 of the curve is an extraordinarily delicate index of 

 small changes in the reaction of the blood. 



Both the plasma and the corpuscles of blood contain 

 substances which enter into chemical combination with 

 C0 2 ; and these combinations dissociate with fall in 

 the pressure of C0 2 , and re-form with rise, just as 

 oxyhaemoglobin dissociates and re-forms. The whole 



