PAET III 



THE DISSOCIATION CURVE CONSIDERED AS AN 

 "INDICATOR" OF THE "REACTION" OF THE BLOOD 



CHAPTER XIV 



THE DISSOCIATION CURVE IN MAN 



WE are now in a position to discuss the dissociation curve in man 

 from what I may call the practical rather than the theoretical side. 

 Firstly, let us consider the constancy of its position in the same person 

 at different times. Secondly, the degree of coincidence in the curves 

 obtained from different persons. Here let me say at the outset that 

 I am only dealing with the individual in his normal condition and 

 not under special conditions such as violent exercise. 



The first question which confronts the worker is whether he is to 

 study the dissociation curve in the presence or absence of carbonic 

 acid. Three possible courses are open : 



(1) To study the dissociation curve in the absence of C0 2 . 



(2) To study it at a standard CO 2 pressure. 



(3) To study it at the C0 2 pressure of the alveolar air of 



the person. 



Each of these courses has something to be said for it, but it is 

 clear that the first two give slightly different information from the 

 third. The third tells of the blood as it actually circulates in the 

 arteries and is the most interesting and most valuable measurement 

 of the three : it tells most about the condition of the individual. But 

 the first and second methods have a value of their own if you wish 

 to inquire whether the blood of all persons is the same ; it is best to 

 study this question under the simplest conditions possible, hence I 

 shall start without the complication of the alveolar air. Nor need the 

 whole curve be studied, let me rather take some convenient pressure of 



