Theories and Experiments 211 



stead of a man we. consider a fish living in submarine depths as great 

 as 400 fathoms ... We should then reach a pressure of 2,272,000 

 pounds. 



The English academicians did not doubt that a man can live at 

 a depth of 200 fathoms. (P. 191.) . ... 



The effects of this pressure on the human body cannot fail to be 

 great; we see that when we place animals under the pneumatic bell. 



The body is subjected to the pressure which presses the blood- 

 vessels, the muscles, and the soft parts against the bones. And since 

 in the humors of the body, in the air passages, in fact, everywhere, 

 there is air kept in a small volume by the pressure, when this pres- 

 sure is removed, the animal swells up all over, from the expansion of 

 the lungs, the intestines, and the air contained in the vessels and even 

 in the cell meshes. (P. 192.) . . . 



But there is a great difference between air rarefied by vapors or 

 that rarefied by the removal of a part of itself, and that air which is 

 lighter because of the altitude and its distance from the center of the 

 earth. In the latter, in fact, although it has lost half its weight, respi- 

 ration takes place without difficulty; this I experienced on the moun- 

 tains Jugo and Furca. (Haller quotes Cassini, Bouguer, etc.) 



And one can even live a long time at these heights ... I agree 

 with Arbuthnot, who teaches that a sudden shift to rarefied air is hard 

 to endure at first, but that one can become accustomed to it. Perhaps 

 that is the reason why birds endure rarefied air more easily than other 

 animals (Derham). It is easy to understand, in fact, that the pressure 

 upon our humors and our vessels will increase in proportion as the 

 outer air becomes denser, and vice versa. (P. 193.) . . . 



We easily understand the disadvantages of rarefied air; we shall 

 see that it cannot inflate the lungs completely. Since 'the pressure no 

 longer sustains the vessels of the body, they resist the heart less and 

 are more easily ruptured. In a very much rarefied air, the danger is 

 increased by the expansion of the air contained in our humors. Light 

 air, which does not fully inflate the lungs, makes the passage of the 

 blood in these organs more difficult, and allowing less blood to reach 

 the left heart in a given time, removes from it the stimulus which 

 urges it to contract. (P. 196.) . . . 



In rarefied air, strength is diminished. In our Alps, those who 

 have lung ailments die when they are in lofty places, especially if it is 

 warm there, for cold moderates the ill effects of rarefied air. The 

 sturdy mountaineers of the Alps carry enormous burdens in lofty 

 places. 



The fever, prostration, slight hemorrhages and hemoptysis, an 

 unfortunate example of which one can find in Scheuchzer, 20- which 

 symptoms certain travellers have experienced while passing through 

 the mountains, I attribute rather to the fatigue of the ascent and to 

 the strain on the respiratory powers. In fact, travellers who are rest- 

 ing or are on horseback have no such symptoms. (P. 197.) 



So, according to the celebrated Swiss physiologist, the effect of 

 the rarefied air has as its principal causes the lessening of weight 

 pressing upon the surface of the body, the dilation of the superficial 



