RESPIRATION 191 



the breathing, as shown by a fall in the alveolar CO 2 pressure. 

 This fact, already referred to in connection with the historical 

 development of the theory of regulation of the breathing by the 

 blood reaction, was brought out in full clearness by the investiga- 

 tions carried out in connection with the Pike's Peak expedition 

 by Miss FitzGerald on persons fully acclimatized at different 

 altitudes. 36 Figure 57 represents graphically her results on this 

 subject. It will be seen that in such persons the alveolar CO 2 pres- 

 sure falls regularly with increase of altitude. In other words the 

 breathing increases in a regular ratio with diminution in the oxy- 

 gen pressure of the inspired air. 



What is the cause of this increase? Since the experiments, 

 already referred to, of Boycott, Ogier Ward, and myself, it has 

 been pretty generally assumed that in response to the stimulus of 

 anoxaemia a slight acidosis, sufficient to account for the increased 

 breathing, develops in the blood. This explanation received strong 

 confirmation from the discovery by Barcroft in the Teneriffe 

 experiments that the dissociation curve of the oxyhaemoglobin of 

 the blood at high altitudes is sensibly the same in presence of the 

 existing alveolar CO 2 pressure as at sea level in presence of the 

 alveolar CO 2 pressure existing there. The extra acid, or dimin- 

 ished available alkali, present in the blood seemed just to compen- 

 sate for what would otherwise be increased alkalinity due to the 

 lowered CO 2 pressure. The physiological facts, however, do not 

 correspond with the lactic acid theory. Moreover no excess of 

 lactic acid could be discovered by Ryffel in the urine and hardly 

 any in the blood, of persons exposed to low pressures in a respira- 

 tion chamber or steel chamber, 37 or indeed in persons at high 

 altitudes ; 38 and no other abnormal acid could be discovered in the 

 blood. Hence the theory of an acidosis due to formation of ab- 

 normal acids cannot be substantiated. In the report of the Pike's 

 Peak Expedition we adopted the theory that the anoxaemia alters 

 the activity of the kidneys in such a way that they regulate the 

 blood to a lower level of alkalinity. 



Another, and essentially similar, theory was adopted by Has- 

 selbalch and Lindhard as the result of experiments in a steel 

 chamber. 39 They found that the excretion of ammonia is markedly 



"FitzGerald, Phil. Trans. Roy. Soc., 203 (B), p. 351, 1913; and Proc. Roy. 

 Soc., 88 (B), p. 248, 1914. See also, Yandell Henderson, Journ. of Biol. Chem., 

 1920. 



"Ryffel, Journ. of Physiol., XXXIX (Proc. Physiol. Soc.), p. xxix, 1910. 



88 See Barcroft, The Respiratory Function of the Blood, p. 260. 



"Hasselbalch and Lindhard, Biochem. Zeitschr., 68, p. 295, 1915. 



