CHAPTER V 



THE EFFECT OF ACID ON THE DISSOCIATION CURVE 



OF BLOOD 



BEFORE entering into a discussion as to whether the influence 

 of " reaction " on the affinity of blood for oxygen is different in 

 nature or only in degree from that of salts, I will state the facts 

 which must form the basis of any such discussion. 



Doubtless the affinity of haemoglobin for oxygen is very sensitive 

 to small changes in acidity or alkalinity. This statement unfortu- 

 nately does not rest on experimental determinations of the influence 

 of minute quantities of acid or alkali on the dissociation curve of an 

 otherwise pure solution of haemoglobin, for no such determinations 

 exist. In the case of acid it remains to be seen whether such an 

 experiment can be carried out without the precipitation of the 

 haemoglobin. What information there is on the subject, then, is 

 derived from experiments on blood and not on haemoglobin. 



In two words, the effect of increased acidity of the solution is to 

 lessen the effective concentration of the oxygen in the solution which 

 contains the haemoglobin. To give a concrete instance, that of my 

 own blood. The presence of 40 mm. pressure of carbonic acid halves 

 the effective concentration of oxygen. In order therefore to pro- 

 duce a given degree of saturation in the presence of 40 mm. CO 2 

 pressure, the concentration of oxygen must be about twice the 

 value which would have sufficed in the absence of the carbonic 

 acid. 



The concentration of free carbonic acid in the solution, necessary 

 for the production of a measurable change in the affinity of haemo- 

 globin for oxygen, is very small, and amounts to something of the 

 order of one part in one hundred million. This fact is directly 

 deducible from the data furnished by Bohr, Hasselbalch and Krogh (1) , 



