380 RESPIRATION 



the rarefied air this would certainly suffice to saturate the arterial | 

 blood to the same extent as at sea level. At 140 mm. of barometric l 

 pressure there would still be at least 53 mm. of alveolar oxygen ; 

 pressure; and it is probable that marked symptoms of oxygen 

 shortage would only begin to appear at pressures below this. At I 

 100 mm, they would become urgent in unacclimatized persons. 

 At 80 mm. Paul Bert's animals were at the point of death. 



It is difficult to see how the addition of CO2 to the inspired 

 oxygen could be of any service, although at moderate diminutions , 

 of pressure CO2 is of considerable service, as already pointed ! 

 out. When pure oxygen is breathed it is impossible to raise the ' 

 alveolar CO2 pressure without lowering the alveolar oxygen pres- j 

 sure; and at very low barometric pressures every millimeter of I 

 alveolar oxygen pressure counts. Moreover rise of alveolar CO2 ! 

 pressure would, on account of the Bohr effect, tend of itself to ■ 

 diminish the percentage saturation of the arterial blood with 

 oxygen and thus counteract any advantage gained by increased 

 rate of circulation. Aggazotti has shown^'' that when animals are 

 placed in oxygen containing a considerable percentage of CO2 

 they are capable of withstanding extremely low pressures; but 

 the same was found by Paul Bert when the atmosphere was one 

 of pure oxygen. Aggazotti himself reached the very low pressure 

 of 120 mm. in a steel chamber while breathing oxygen with CO2 

 added. 



To make it safe to go much above 30,000 feet it would be 

 necessary to have an apparatus which made it certain that the 

 wearer always breathed pure oxygen, or at any rate oxygen not 

 mixed with any other gas than CO2. An ordinary mine-rescue 

 apparatus with the usual constant oxygen supply of about 2 liters 

 per minute (measured at ordinary atmospheric pressure) would 

 secure this result with a very moderate expenditure of oxygen. 

 Care would, however, be necessary to insure that both the purifier 

 and the oxygen supply worked properly at the low temperature 

 and pressure met with at very high altitudes. With a larger con- 

 sumption of oxygen an apparatus could be made to work safely 

 without a purifier. If it were required to go much above 40,000 

 feet, and to a barometric pressure below 130 mm., it would be 

 necessary to inclose the airman in an air-tight dress, somewhat 

 similar to a diving dress, but capable of resisting an internal pres- 

 sure of say 130 mm. of mercury. This dress would be so arranged 



"Aggazotti, ArcA. Hal. de Biologie, XLVI, 1905. 



