202 RESPIRATION 



the alveolar CO 2 pressure showed that it was about a fourth deeper 

 than it otherwise would have been. On the physiological evidence, 

 therefore, the fall in PH was only about .003, instead of .12, or 

 only one-fortieth as much as calculated. From this example it 

 would seem to follow that Hasselbalch's method, when extended 

 to abnormal blood, is as unreliable as that of Barcroft and Peters. 

 Further investigation as to methods of determining hydrogen ion 

 concentration in abnormal blood seems to be much needed. 



Except by observation of physiological reactions, there seems at 

 present to be no method of estimating in a reliable manner the 

 small variations in PH which are of so much physiological impor- 

 tance. Hasselbalch estimates that a difference of .03 can be detected 

 in single determinations by the electrometrical method ; but this is 

 a very large difference, corresponding to an increase of 250 per 

 cent in the breathing. The colorimetric method by means of indi- 

 cators is equally rough. Time and effort will continue to be wasted 

 on futile measurements until the extreme fineness of the physio- 

 logical regulation of PH in the blood and tissues is more fully 

 realized. 



On account of various sources of error, already alluded to, in 

 the electrometrical or other measurements of PH, we are still with- 

 out much very exact information as to the permanent steadiness 

 during health of the alkalinity of the blood under resting condi- 

 tions. In this connection some very interesting observations have 

 been made by Hasselbalch and Gammeltoft on the PH of the 



