1034 Summary and Conclusions 



depths have shown that it contained less oxygen than surface 

 water. According to Lant Carpenter, 10 the water of the ocean 

 would contain, on the average, no matter what the depth, 2.8 

 volumes of gas per 100 volumes of water; this gas would be con- 

 stituted as follows: 



100.00 100.00 



And so, less oxygen and a little less nitrogen. From this there 

 appear two conclusions: 



First, a stay in the depths does not subject the animals to any 

 danger coming from decreased oxygen tension. In the second 

 place, sudden decompression should produce no harmful effect upon 

 the animals of the depths because they will not have an excess of 

 nitrogen dissolved in their tissues; and the truth of this is borne 

 out by the fact that no free gases have ever been found in the 

 tissues of a fish or an invertebrate brought up by the drag. 



Circumstances would be greatly changed if some source of air 

 should suddenly gush up from the bottom of the sea. It would 

 need to come from only 100 meters, if it were chemically pure, to 

 kill rapidly all the beings it met on its way. 



If we consider, for air-breathing animals as well as aquatic 

 animals, not the present epoch, but geological ages, we have every 

 reason to think that barometric pressure must have played an 

 important part in the appearance and the modification of life on 

 the surface of the globe. In the first ages of our planet, indeed, 

 the oxygen tension must have been much greater than today for 

 two reasons: the atmosphere was higher and its oxygen content 

 greater, since the rocks were not yet cooled and oxidized to so 

 great a depth. The epochs which follow us will no doubt see the 

 air enter further and further into the depths of the ground and 

 the oxygen diminish in it in growing proportion. So it is per- 

 missible to imagine that there was a time when present beings 

 could not have lived on the ground because of too great oxygen 

 tension, and that a time will come when they can no longer live 

 on account of its too weak tension. To go beyond this first plausible 

 hypothesis would be to adventure into the pure realm of fancy; 

 we shall leave to others this attractive and easy occupation. 



