82 NOTES OF A NATURALIST. 



frequently felt at lower elevations, and that the human 

 economy is able so readily to adapt itself to the 

 altered conditions when transferred to an atmosphere 

 of say two-thirds of the ordinary density, where the 

 diminished supply to the lungs is aggravated by the 

 increased mechanical effort requisite to move the limbs, 

 and raise the weight of the body in an attenuated 

 medium. Observation shows that the effects actually 

 produced at great heights vary much with different 

 individuals, and that in healthy subjects the functions 

 after a short time adapt themselves to the new con- 

 ditions. It is obvious that this process must have a 

 limit, which has probably been very nearly attained 

 in some cases. 



In spite of some statements lately published, I am 

 inclined to believe that the utmost limit of height 

 compatible with active exertion will be found to lie, 

 according to individual constitution, between twenty 

 and twenty-five thousand feet. As regards our ex- 

 periences at Chicla, the difficulty is to account for the 

 fact that the effects produced while the body is at 

 rest should disappear during active exercise ; and 

 whatever the nature of the disturbance of the func- 

 tions, this was not accompanied by any discernible 

 derangement of the respiration or the circulation. It 

 appeared to me that the seat of disturbance, such as 

 it was, was limited to the nervous system. 



On the evening of our arrival we met at the hotel 

 the commandant of the Chilian detachment, and on 

 presenting my letter from the commander-in-chief, he 

 was profuse in offers of assistance. It was speedily 

 arranged that we should start on the following morn- 



