316 Historical 



men and animals ascend to great heights above sea level, they 

 always finally experience a series of more or less serious symp- 

 toms, the combination of which constitutes mountain sickness. 



The very existence of these symptoms, however, has been 

 denied, as we have seen; but these denials, which are rash and 

 unscientific generalizations upon a few isolated cases, do not merit 

 our attention here. 



The first striking fact, when we examine the series of data 

 which we have collected, is the difference in altitude at which the 

 dangerous symptoms appear, depending upon whether we are 

 dealing with mountain journeys or balloon ascensions. Whereas 

 in the first case travellers often become ill at about 3000 meters, 

 and almost never mount above a height of 5000 meters without 

 serious suffering, Gay-Lussac, Barral and Bixio, and M. Glaisher 

 felt only a few slight disturbances at 7000 meters. In a moment, 

 we shall easily find the reason for this enormous difference. 



On earth as in the air, the severity of the symptoms keeps 

 increasing with the altitude; but in its ascending progress, it 

 follows a law of progression, not of proportion. Up to 3000 meters, 

 a traveller who set out from the level of the valley, 1000 meters 

 for example, will be warned of the decrease of pressure only by 

 a slight increase in pulse and respiratory rates; from 3000 meters 

 to 4000 meters, the symptoms increase considerably in intensity; 

 above that, each ascent of a few hundred meters is marked by a 

 progressively increasing aggravation of them, and a moment comes 

 when it is harder to climb 50 meters than it was to ascend 500 

 meters at the beginning of the journey. It is not surprising, 

 therefore, to see, as Captain Gerard reported, mountaineers of 

 Koonawur, accustomed to observing sensations of this sort, esti- 

 mate the altitude of the point which they have reached by the 

 difficulty in breathing experienced there. 



The altitude at which the symptoms of mountain sickness 

 appear varies considerably in the different regions of the earth. 

 We have seen that in the Pyrenees serious symptoms appear only 

 near the highest summits, that is, above 3000 meters and then they 

 are very rare. At the same level in the Alps the accounts of trav- 

 ellers begin to indicate some disturbances; they are rather 

 customary between 3500 and 4000 meters; above that, their exis- 

 tence constitutes a rule from which far fewer persons escape than 

 the editors of the Alpine Clubs would have us believe. Etna, with 

 its 3313 meters, is in this respect, as we have said, a limited moun- 

 tain, as is the Peak of Teneriffe (3716 meters). In the Caucasus 

 and the mountains of Armenia the level at which almost everyone 



