READJUSTMENTS OF REGULATION 49 



age results of measurements of alveolar CO2 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 CO2 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 CO2 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 COg 

 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 COo pressure 

 depends on the existing alveolar oxygen pressure. 



What is the significance of the fall in alveolar CO2 

 pressure at low barometric pressures? It might be 



