1 84 RESPIRATION 



As already pointed out this curve is shifted to the right or left with 

 varying alkalinity, and the shifting is a moderately delicate index 

 of the variation (Chapter III). Peters, 25 working with Barcroft, 

 has shown that the shifting with variations in CO 2 pressure de- 

 pends on the shifting of PH. Hence the constancy of the dissocia- 

 tion curve appeared to be a direct index of the constancy in PH of 

 the blood. The lowering of alveolar CO 2 pressure at high altitudes 

 seemed therefore to be just sufficient to keep the PH of the blood 

 steady in so far as direct methods enable us to measure the degree 

 of steadiness. As will be seen below, however, there is physio- 

 logical evidence that the blood is actually more alkaline at high 

 altitudes. More recently Hasselbalch and Lindhard have made 

 direct electrometric measurement of PH in a steel chamber after 

 exposure of sufficient duration to the low pressure, and their 

 measurements give practically the same result. 26 The resting al- 

 veolar CO 2 pressure on Pike's Peak was about 27 mm., or 13 mm. 

 below that at sea level. Raising the alveolar CO 2 pressure on Pike's 

 Peak to 40 mm. would have caused the extremest panting. 



As soon as the results of Hasselbalch and Lundsgaard were 

 published, it was possible to estimate quantitatively the delicacy 

 with which the respiratory center responds to variations in the 

 reaction of the blood : for the delicacy of the reaction of the center 

 to variations of CO 2 pressure was known from our previous ex- 

 periments, while the curves of Hasselbalch and Lundsgaard made 

 it possible to convert variations of CO 2 pressure into variations of 

 PH in the blood. Some confusion arose, however, owing to the 

 fact that Lindhard, 27 and Hasselbalch and Lindhard, 28 had mean- 

 while published experiments which seemed to indicate that the 

 respiratory center in man is commonly far less sensitive to CO 2 

 than Priestley and I had found. The matter was therefore rein- 

 vestigated by Campbell, Douglas, Hobson, and myself. 29 We 

 found that the Danish observers had been deceived, owing to a 

 faulty modification of the method of sampling the alveolar air. 

 The fresh experiments gave practically the same results as Priest- 

 ley and I had obtained, so we could make the calculation accord- 

 ingly. 



A rise of 0.2 per cent or 1.5 mm. in the CO 2 pressure of the 



"Barcroft, The Respiratory Function of the Blood, p. 316, 1913. 



28 Hasselbalch and Lindhard, Biochem. Zeitschr., 68, p. 293, 1915. 



87 Lindhard, Journ. of Physiol., XLII, p. 337, 1911. 



88 Hasselbalch and Lindhard, Skand. Arch. f. Physiol., XXVIII, 1911. 



29 Campbell, Douglas, Haldane, and Hobson, Journ. of Physiol., XLVI, p. 301, 

 1913- 



