1 88 RESPIRATION 



the peculiar shape of the dissociation curve of the oxyhaemoglobin 

 in blood is correct, alter the shape of the dissociation curve. 



In a quite recent paper Lovatt Evans^^ has shown that the Ph 

 of blood as determined colorimetrically by an indicator method 

 is as much as 0.2 higher than when determined electrometrically. 

 He has also shown pretty conclusively that the electrometric 

 method has an error owing to the formation of formate from 

 carbonate by catalytic action at the electrode, so that the Ph of 

 blood is higher by 0.2 than appears from the electrometric de- 

 terminations. The new colorimetric method of Dale and Evans^^ 

 seems to avoid several defects inherent in the electrometric method 

 as applied to blood. 



On the existing evidence, and allowing for mistaken inferences 

 which have been drawn in ignorance of the peculiar properties of 

 haemoglobin (as it exists in the red corpuscles) in regulating the 

 Ph of blood, it seems evident that during health the regulation 

 of the reaction of the arterial blood is carried out with a delicacy 

 and constancy of which we can at present only obtain a real con- 

 ception by physiological observations. The foregoing discussions 

 show that there are at least three regulators of the reaction — the 

 lungs, the kidneys, and the liver. We can also now form a general 

 conception of how these regulators act under ordinary conditions. 



The part played by the lungs in this regulation is, quite clearly, 

 to deal rapidly with variations in reaction due to varying pro- 

 duction of CO2, and particularly to the rapid variation caused by 

 varying muscular exertion. By keeping the alveolar CO2 pressure 

 approximately normal, the action of the lungs keeps the arterial 

 CO2 pressure approximately normal ; and so long as the dissocia- 

 tion curve for CO2 in the blood is also kept normal by other means 

 the reaction of the arterial blood is also kept almost exactly 

 normal. If, however, owing to rapid production of lactic acid in 

 muscles, rapid secretion of gastric or pancreatic juice, or other 

 causes, the dissociation curve for CO2 is temporarily disturbed, the 

 breathing compensates approximately at once for the disturbance 

 in blood reaction. 



The part played by the kidneys seems also clear. They not only 

 respond to the minutest variations in blood alkalinity by secreting 

 more acid or more alkaline urine, but also tend to keep normal the 

 proportion of soda and potash and other crystalloid substances 

 existing in the blood. In this way the dissociation curve of the COj 



"Lovatt Evans, Journ. of Physiol., LIV, p. 353, 1921. 

 "Dale and Evans, Journ. of Physiol., LIV, p. 167, 1920. 



