1032 Summary and Conclusions 



sion shows its effects by paraplegia, recompression must be car- 

 ried on at once, without losing time in inhaling oxygen, especially 

 when the symptom did not appear until some time after the return 

 to the open air, for in this case we have to do, not with a general 

 obstruction of the pulmonary circulation, but with some bubble 

 of gas lodged in the vessels of the medulla, whose volume must be 

 reduced at once so that the blood may drive it out. 



Workmen employed in compressed air may suffer other dis- 

 comforts which, though less serious, should not be completely dis- 

 regarded. Sudden expansion of the intestinal gases and the froth 

 formed in the liquids of the digestive tract may have consequences 

 which are annoying for the digestion and contribute to these dis- 

 turbances of the appetite which have often been noticed. 



Moreover, the air in which they stay is anything but whole- 

 some. In the caissons of the bridge of Kehl, M. Bucquoy found 

 2.377o of carbonic acid (p. 373), and when the pressure rose 

 to 3V2 atmospheres, the workmen were, as we have proved, in the 

 same condition as if, at normal pressure, they had breathed air 

 containing 2.37 x 3.5 = 8.3% of CO.; and surely, such an atmosphere 

 would not be without danger. In the same way, other gases, the 

 carbon monoxide of incomplete combustions, the gases produced 

 by the explosions sometimes used in mines, or those wliich rise 

 from the ground, act in the double ratio of their percentage and 

 the manometric pressure; we have seen (p. 717) how quickly a 

 few drops of ether cause anesthesia in compressed air. We see 

 that energetic ventilation is absolutely necessary, and this point 

 has not been sufficiently emphasized, because the multiplying ef- 

 fects of pressure on the action of toxic gases were not known. 



5. Conclusions from the Point of View of General Natural 

 History. 



While speaking of diminished pressure, we have shown briefly 

 the part it plays in the general conditions of life on the earth and 

 in the geographical distribution of animals or plants. 



The study of present nature shows us nothing comparable from 

 the standpoint of increased pressure, at least if we consider air- 

 breathing living beings: the few regions which are a little below 

 sea level (valleys of the Dead Sea and the Caspian) can hardly be 

 called populated. But the case is quite different, or at least it 

 seems so, for the beings which live in the waters of the sea at 

 depths which reach 4000 and 5000 meters. 



First, if we consider in their habitat the creatures of the greatest 



