RESPIRATION 1 85 



alveolar air and arterial blood causes an increase of about 100 per 

 cent in the resting alveolar ventilation, and from Figure 54 it 

 will be seen that this corresponds to a difference of .012 in Ph. 

 This difference, large as its physiological effect is, cannot be de- 

 tected with certainty by the electrometric method, or by indicators, 

 and is quite undetectable by the shifting of the dissociation curve 

 of oxyhaemoglobin. Nevertheless a twentieth of this difference 

 would produce an easily measurable effect on the breathing or 

 alveolar CO2 pressure. The astounding delicacy of the regulation 

 of blood reaction is thus evident. No existing physical or chemical 

 method of discriminating differences in reaction approaches in 

 delicacy the physiological reaction. Unfortunately, however, the 

 quantitative significance of our calculation has not yet been ap- 

 preciated. The blood within the living body is still treated as if 

 its reaction were not only variable, during rest, as it is, but capable 

 of showing the variations by the existing very rough chemical and 

 physical reactions. One might as well try to cut delicate histo- 

 logical sections with a blunt carving knife, as try to demonstrate 

 ordinary very minute changes in blood reaction by the existing 

 physical and chemical methods. 



It was discovered by Christiansen, Douglas, and myself, as 

 previously set forth, that the reduction of oxyhaemoglobin, as 

 this occurs in the course of the circulation, has an effect re- 

 sembling that of the addition of alkali to the blood. Thus the 

 CO2 pressure of the blood in the systemic capillaries is pre- 

 vented from rising nearly as high as it would otherwise do. The 

 hydrogen ion concentration of the blood is also prevented from 

 rising in correspondence with the actual greatly restricted increase 

 in CO2 pressure. Accordingly the actual increase of hydrogen ion 

 concentration in mixed venous as compared with arterial blood 

 must be very small. In this way the extraordinarily delicate regu- 

 lation of the reaction of arterial blood becomes much more intelli- 

 gible, as venous blood must be very little less alkaline than arterial 

 blood. In determining the hydrogen ion concentration of blood by 

 the ordinary electrometrical method it is necessary to reduce the 

 blood first, as the presence of oxygen interferes with the action of 

 the hydrogen electrode. ^^ Thus the determination is made on re- 

 duced, or by Barcroft's method on partially reduced, blood, but 

 with a CO2 pressure corresponding to that of arterial blood. It is 



'"Peters, Journ. of Physiol., 48, Proc. Phys. Soc, p. vii, 19 14. It is probable 

 that owing to incomplete reduction the values obtained by Hasselbalch have been 

 slightly too low. 



