READJUSTMENTS OF REGULATION 57 



acclimatisation, be practically as fully saturated as 

 usual ; and considering the increase in the haemoglobin 

 percentage the amount of oxygen in the arterial blood 

 must be greater than normal. The oxygen consump- 

 tion during rest was the same on Pike's Peak as at 

 sea level, and the circulation rate, so far as our tests 

 could determine it, was about the same.^ Hence the 

 oxygen pressure in the capillaries of the body would 

 be somewhat higher than usual, and our unusually 

 rosy color seemed to confirm this. 



The most probable explanation as to how oxygen 

 want produces these effects is that there is some sub- 

 stance which normally undergoes almost complete oxi- 

 dation in the lungs at each round of the circulation. 

 At high altitudes it escapes past the lungs in abnormal 

 quantity in consequence of the lowered oxygen pres- 

 sure, and probably also of the longer time required by 

 the blood in the lungs to reach its full oxygen pres- 

 sure. There are many facts pointing to the assump- 

 tion that such a substance exists and that its presence 

 in the blood is the source of various phenomena accom- 

 panying oxygen want. 



The increase in the capacity of the lung epithelium 

 to secrete oxygen is comparable to the increased 

 efficiency produced in almost any organ by increased 

 use. This increased capacity suggests the probable 

 explanation of why in the original human experiments 

 of Lorrain Smith and myself we obtained much more 



1 By more accurate tests Krogh and Lindhard have re- 

 cently shown definitely that there is no alteration in the 

 circulation rate after acclimatisation in a steel chamber. 



