692 



Experiments 



asphyxia at a degree of oxygen lack and in expanded air at a de- 

 gree of decompression in which the oxygen tension is identical. 

 So, in dogs, respiratory disturbances appear in confined air at 

 about the time when there is only 12 per cent of oxygen; in pure 

 air, they appear at about the pressure of 43 cm., a pressure which 

 is met at about 5000 meters altitude; in both cases the oxygen ten- 

 sion is the same, for 12 x 76 = 20.9 x 43.6. As to serious symptoms, 

 nausea, etc., the proportion of oxygen in the confined air must 

 drop to about 8 per cent, or the barometric pressure of the pure 

 air must be reduced to about 30 cm., which corresponds to a height 

 of 7300 meters; the oxygen tension is the same in both cases. 



Fig. 54 — Maxima and minima of cardiac pressure in asphyxia without 

 carbonic acid. 



Now — new confirmation — , it is at these altitudes approximately 

 that the symptoms and disturbances which constitute "balloon 

 sickness" occur in aeronauts, motionless in their basket. 



The agreement becomes still more interesting when it concerns 

 observations on man himself. 



The most important are contributed by M. Felix Leblanc, 2 

 who had the opportunity to analyze the air of the mines of Poul- 

 laouen and Huelgoat, in Brittany, whose treatise contains valuable 

 information about the sensations of the miners. 



The pyrites which are present in abundance in the veins being 

 worked combine with a part of the oxygen in the air, which is 

 thus lessened without being tainted at the same time by carbonic 

 acid or other gases, as happens in confined places. 



From the data reported by M. Leblanc we extract the following: 



A: In a place where there is only 16.7 per cent of oxygen, 

 respiration is only slightly affected, but the air is considered 

 "weak" by the miners; 



