242 RESPIRATION 



ally to a high altitude. There is, however, much more in this 

 acclimatization than mere increase in the power of oxygen secre- 

 tion, since there is also the gradual adjustment of blood reaction 

 to increased breathing, as explained fully in Chapter VIII. 



In a more recent series of experiments by Kellas, Kennaway, 

 and myself 28 these two effects were separated. One of our objects 

 was to see how far acclimatization to high altitudes could be ob- 

 tained by discontinuous exposures to low barometric pressures. 

 This question is of course of considerable importance to airmen, 

 in whom the exposures are discontinuous. The effects produced 

 before acclimatization on Dr. Kellas, myself, and others, by an 

 exposure to 320 or 330 mm. barometric pressure, are described 

 in Chapter VI. To obtain acclimatization we used the method of 

 exposing ourselves for six to eight hours to atmospheric pressures 

 of 500, 430, and 360 mm. on three successive days. We found, how- 

 ever, that our resting alveolar CO 2 pressure had always returned 

 to normal before the morning after each successive exposure. 

 Thus there was no lasting adjustment of blood reaction to in- 

 creased breathing, as any change in this direction had disappeared 

 by the morning. There was also no lasting increase in our haemo- 

 globin percentages. Any acclimatization obtained must therefore, 

 apparently, be due to increased power of oxygen secretion. 



The result of the experiment was that there was marked ac- 

 climatization, but limited in amount. When unacclimatized I had 

 been totally disabled, and had lost all memory, at a pressure of 

 320 mm., as already described. But on the last day of the ac- 

 climatization we stayed at 315 mm. for a considerable time, during 

 which, though we were distinctly blue, I could quite easily con- 

 tinue to do gas analyses and other operations, and move about 

 as usual, with no loss of memory afterwards of what had occurred. 

 In this experiment my son, Captain J. B. S. Haldane, acted as an 

 unacclimatized control. He came in with us and stayed for some 

 time at 366 mm. ; but after two hours he was so much affected that 

 we had to let him out. His breathing had become increasingly 

 rapid and shallow, and he had gradually sunk into a stupefied 

 condition. After coming out he could remember hardly anything 

 of the last hour in the chamber. 



It is clear from this experiment that airmen, so long as they 

 retain their health, and remain at high altitudes pretty fre- 

 quently, must be capable of acquiring a considerable degree of 



28 Haldane, Kellas, and Kennaway, Journ. of Physiol., LIII, p. 181, 1919- 



