vi INTRODUCTION. 



general^ leading features. Nausea and vomiting ; headaches of most 

 severe character ; feverishness ; hemorrhages ; lassitude^ depression 

 and weakness, and an indescribable feeling of illness, have been re- 

 peatedly mentioned as occurring at great elevations, and have only 

 been cured by descending into lower zones. To these maladies 

 the term mountain-sickness is now commonly applied. 



It is very generally admitted that mountain-sickness should 

 be attributed to the diminished atmospheric pressure (or, as it is 

 termed, to the rarefaction of the air) which is experienced as one 

 goes upward. Yet, in various parts of the world, the notion is, and 

 has long been entertained, that it is due to local causes, such, for 

 example, as noxious exhalations from vegetation. Some sujDport to 

 this notion seems to be found in the fact that whilst the greatest 

 heights in Europe (15-16,000 feet) are annually ascended by 

 throngs of persons without perceptible inconvenience, multitudes 

 of others in Asia and America sulfer acutely at lower elevations 

 (14-15,000 feet) ; and it would therefore seem that there are influ- 

 ences at work on the latter continents which do not operate in 

 Europe. The apparent discordance is explicable without having 

 recourse to local influences, which could not be deemed sufficient 

 to account for the eifects in general, even if they might be enter- 

 tained in particular instances. AYhilst the assumed causes are 

 local, the observed effects are world-wide ; and no cause would be 

 adequate to account for the effects except one operating in every 

 clime and at all times. 



But, although it is very generally admitted that the evils which 

 have been enumerated are due to diminished atmospheric pressure, 

 many persons are unconvinced that such is the true explanation, 

 especially those who are accustomed to travel amongst the mount- 

 ains of Europe ; and it is pointed out, apparently with force, that 

 the whole of the symptoms can be produced by other causes, and 

 that aeronauts have sometimes attained higher elevations than have 

 ever been reached on the earth, and have scarcely been affected 

 at all. It is argued that some persons are predisposed to nausea. 



