CHAPTER IV. 



THE EXTERNAL ENVIRONMENT (continued). 



183. Atmospheric Pressure below Ground Level. Below the 

 ground, in a mine, the atmospheric pressure is greater than on 

 the surface. The increase of the proportion of oxygen in the air, 

 which follows, does not modify in the least the value of the 

 respiratory exchanges. At the ordinary depths of a mine it 

 cannot be" the pressure which causes physiological troubles. All 

 the more so that the increase is very small ; the rate of the oxygen 

 varies, therefore, very little, and experiment has shown clearly 

 that the respiration remains normal, f 1 ) It was found, in this 

 latter case, that the blood was merely momentarily over- 

 saturated ; ( 2 ) but this phenomenon must be absolutely uncertain, 

 having escaped a number of observers. ( 3 ) 



Far from being in contact with a super-oxygenated atmosphere 

 miners are exposed to breathing deleterious gases. Notably 

 carbon-dioxide and carburetted hydrogen (fire damp). The heat 

 the humidity and the darkness of underground workings exert 

 a certain influence on the workers. 



The heat is due to the depth. If the outside temperature at 

 the surface is 10 C., that at 1,500 metres is 50-55. There is 

 also a higher degree of humidity. Labour in a hot and humid 

 atmosphere is, from what has already been explained, very 

 troublesome ( 174). In such conditions 25 is a hardly bearable 

 limit ; so that after a depth of 700 to 800 metres the hottest 

 parts of the mine have to be cooled by sending down cold air to 

 mix with the hot.( 4 ) 



The effect of darkness will be examined later ( 187). 



Highly compressed air presents more dangers than the slightly 

 overcharged air of the mine. The proportion of oxygen, which 

 is notably increased, is not the cause, and entails no evil conse- 

 quences. But it is in no wise immaterial that the organism 

 should suffer successive compressions and relaxations, especially 

 if these are produced suddenly and without very great precau- 

 tions. The troubles which follow from a stay in compressed air 

 can be extremely serious. They are shown in workmen em- 

 ployed in caissons and in divers. They suffer from caisson sick- 



Regnault (Ann. Ch. Phys., 1849, vol. xxvi., p. 299) ; de Saint-Martin 



p. 96), 

 ( 2 ) Falloise (Trav. Lab. Fred6ricq, 1896-1901) ; A Dung (Arch./. Physiol., 



(Reck. Expir. sur la Respiration, Paris, 1893 



1903, suppl. p. 209). 

 () Schaternikoff (Arch. f. Physiol., 1904, suppl. p. 135). 

 () Dietz (Zeitsch. f. Die Gesamte Kaelte- Industrie, Dec., 1911). 



