READJUSTMENTS OF REGULATION 49 



age results of measurements of alveolar CO z pressure 

 made by Miss Fitz Gerald, in connection with the 

 Pike's Peak Expedition, on persons residing perma- 

 nently at different altitudes. It will be seen that the 

 alveolar C0 2 pressure diminishes regularly with alti- 

 tude, starting from sea level. That this diminution 

 is a response to the diminished alveolar oxygen pres- 

 sure there can be no doubt. If the barometric pres- 

 sure is kept steady, and the oxygen pressure is dimin- 

 ished by lowering the percentage of oxygen, the re- 

 sults are precisely the same, so far as can be judged by 

 the available observations; and, as was first clearly 

 pointed out by Paul Bert, practically all the physiologi- 

 cal disturbances produced by low barometric pressures, 

 or high altitudes, are due to lowering of the oxygen 

 pressure. 



From Figure 3 it is pretty evident that if the oxygen 

 pressure is raised above the normal value at sea level, 

 the alveolar C0 2 pressure will rise still higher. That 

 this is actually the case has recently been shown by 

 Hasselbalch and Lindhard, who have confirmed in a 

 steel chamber many of the Pike's Peak results, and 

 have added further observations of their own. It 

 appears from their results that the alveolar C0 2 

 pressure does not rise much higher after the normal 

 oxygen alveolar oxygen percentage has been exceeded ; 

 but the fact that there is a rise is of great interest, as 

 showing that even the "normal" alveolar C0 2 pressure 

 depends on the existing alveolar oxygen pressure. 



What is the significance of the fall in alveolar C0 2 

 pressure at low barometric pressures? It might be 



