RESPIRATION 237 



due to the rarefied air at 14,000 feet did not produce active secre- 

 tion of oxygen inwards. We used the same method as at Oxford, 

 taking every precaution against errors. The results were quite 

 unmistakable. We found that as soon as acclimatization to the air 

 was established the arterial oxygen pressure became considerably 

 higher than that of the alveolar air. The next table shows our 

 results. In ordinary resting experiments on acclimatized persons, 

 the arterial oxygen pressure was on an average about 70 per cent 

 above the alveolar oxygen pressure. When, however, air extra 

 rich in oxygen was breathed, so that the alveolar oxygen pressure 

 rose to about what it is at sea level, the difference between arterial 

 and alveolar oxygen pressure fell to 8 or 10 per cent, even during 

 the short period of an experiment. In a subject investigated im- 

 mediately on arrival at the summit by the cogwheel railway the 

 arterial was only about 15 per cent above the alveolar oxygen 

 pressure, whereas three days later, after acclimatization, the ex- 

 cess was 100 per cent. 



The Pike's Peak results threw much new light on oxygen secre- 

 tion by the lungs, and on the former experiments at Oxford. It 

 was evident, that not only is oxygen want a stimulus to active 

 oxygen secretion by the lungs, but that the response to the stimulus 

 improves greatly with practice or "acclimatization," just as is 

 the case with other physiological responses. We can now see why 

 some experiments — for instance those which Lorrain Smith and I 

 made jointly on ourselves, indicated oxygen secretion, while other 

 experiments in which the physical and chemical conditions seemed 

 to be the same gave negative results. It was the physiological con- 

 ditions which were different. In the latter experiments we were 

 not acclimatized against anoxaemia. 



It is easy to see the physiological advantage of oxygen secretion 

 as a defense against the anoxaemia of high altitudes and similar 

 conditions, or against carbon monoxide poisoning; but its uses 

 under ordinary conditions, where nothing but pure air at about 

 ordinary atmospheric pressure is breathed, are not so obvious. It 

 is clear that as the arterial haemoglobin is nearly saturated with 

 oxygen, during rest, at any rate, without any active secretion, 

 hardly anything could be gained by secretion, since any additional 

 oxygen which could be added to the blood would be trifling in 

 amount unless with an enormous secretory pressure such as has 

 never been found experimentally. We can thus readily under- 

 stand why there is no secretion during rest under normal condi- 

 tions, as our experiments clearly showed to be the case. It was 



