Summary and Discussion 323 



excessive susceptibility, since, according to Poeppig and Tschudi, 

 they cannot live above 4000 meters (pages 40, 46) . However, we 

 must note that, in the opinion of Tschudi and Elliotson, animals 

 born on the mountains are not as sick as the others. 



But it must be admitted that all of this relates to imported 

 domestic animals. The' native species seem very comfortable at 

 the greatest heights; only Captain Webb saw yaks attacked by the 

 sickness (page 134); llamas seem completely immune, and in the 

 free state graze at altitudes of more than 4000 meters. Since the 

 time of Ulloa, everyone has been struck with astonishment at the 

 sight of condors soaring habitually at 4000 or 5000 meters, and 

 sometimes above 7000 meters; in the Himalayas, the lapwings and 

 other sparrows live at altitudes of more than 5000 meters. 



Here we are dealing with one of the most interesting points 

 of this birdseye view of the subject. The influence of habit or 

 custom on mountain sickness is undeniable; but its conditions have 

 been both exaggerated and poorly determined. 



On the testimony of d'Orbigny, Poeppig, Gay, Tschudi, and 

 Guilbert, one can become quite accustomed to living in the lofty 

 regions of the Andes, and the often unendurable distress which 

 attacks the European in the early part of his sojourn gradually 

 disappears. "In the streets", says Guilbert, "it is easy to distinguish 

 the newcomers; every forty or fifty steps they stop for a few 

 seconds" (page 54) . Analogous effects have been noted on our 

 European mountains; a novice who, when newly arrived from the 

 plains, is sick at a low altitude, can later make much higher ascents 

 with impunity. But we must not think that this immunity is 

 absolute; a fairly great change in level or peculiar circumstances 

 may suddenly bring on the sickness that had disappeared; we 

 shall find the proof of that in the accounts of M. Weddell, M. 

 Pissis and d'Orbigny himself. In a word, the same thing is true 

 of arrival in the mountains as of all sudden changes to which we 

 may be subjected; the passage of a certain time' permits the 

 reestablishment of the equilibrium which was shaken for an 

 instant, and which slower transitions would have left unaltered. 



We shall try later to determine the nature and the importance 

 of the conditions changed by the act of ascent; but even now we 

 can assert the reality of habit or, as we usually say, acclimatization 

 to lofty places. 



But here, as we cannot repeat too often, we are dealing only 

 with the violent and sudden symptoms of mountain sickness, in a 

 word; we have no intention of plunging into the delicate and com- 

 plex study (in which the means of demonstration are the more 



