214 Historical 



absolutely cannot continue; whereas, on a lofty mountain, one is some- 

 times so exhausted that, to avoid most imminent danger, he would 

 literally not take four steps more, perhaps not even one step. For if 

 one persists in making efforts, he is attacked by palpitations and such 

 rapid and hard throbbing in all the arteries that he would fall in a 

 faint if he increased the palpitations still more by continuing to ascend. 



However, and this forms the second characteristic of this strange 

 kind of fatigue, the strength is restored as quickly, and apparently as 

 completely, as it was exhausted. Mere cessation of movement, even 

 if one does not sit down, and in the short space of three or four min- 

 utes, seems to restore the strength so perfectly that when one starts 

 walking again, he is convinced that he will ascend even to the summit 

 of the mountain all in one breath. Now on the plain, a fatigue as 

 great as that of which we have been speaking does not pass away so 

 quickly. 



560. — One would be tempted to ascribe these effects to the diffi- 

 culty in breathing; it seems natural to believe that this rare and light 

 air does not expand the lungs sufficiently, and that the organs of 

 respiration are tired by the efforts they make to supply it, or that, 

 since the duty of this vital function is not completely carried out, and 

 since the blood, according to the theory of M. Priestley, is not suffi- 

 ciently supplied with its phlogiston, the whole animal economy is dis- 

 turbed by it. 



But what persuades me that this is not the real reason for these 

 effects is that one feels fatigued, but not at all oppressed; if the painful 

 action of climbing a steep slope makes the respiration shorter and 

 more difficult, this inconvenience is felt on low as well as on high 

 mountains, and yet does not produce in us, when we climb these low 

 mountains, the effect which we experience on those which are very 

 lofty; moreover, on the latter, when one is quiet, he breathes with the 

 greatest ease. Finally, and this consideration appears to me conclu- 

 sive, if it was imperfect respiration which produced this prostration, 

 how could a few instants of rest taken while breathing this same air 

 seem to restore the strength so completely? 



561. — I am inclined to believe instead that these effects should 

 be attributed to the relaxing of the vessels caused by the decrease of 

 the compressing power of the air. 



Because we are accustomed to living compressed by the weight of 

 the atmosphere, we hardly think of the action of this weight and its 

 effect upon the animal economy. However, if one reflects that at sea 

 level every part of the surface of our body is laden with the weight 

 of a column of mercury 28 inches high, that a single inch of this fluid 

 exerts upon a surface one foot square a pressure equivalent to 78 

 pounds, 11 ounces, 40 grains, marc weight; that consequently 28 inches 

 exert on this same surface the pressure of 2203 pounds, 6 ounces; and 

 that therefore, reckoning ten square feet of surface for a man of 

 average height, as is usually done, the total mass of weight which 

 compresses the body of this man is equivalent to 22,033 pounds, 12 

 ounces; if we consider what must result from the action of this 

 weight, we shall see that it must compact all parts of our body, that 

 it binds them together, so to speak, that it compresses the vessels, that 



