CHAP. XIX. SU3131ARY OF OUR EXPERIENCES. 367 



AVhile there is not the least doubt that they are directly or 

 indirectly produced by diminution in atmospheric pressure, many 

 writers (even amongst those who are well convinced that this is 

 the true cause) continue to speak, when discussing mountain- 

 sickness, solely of elevation above the level of the sea and ignore 

 pressure ; and in this way help to perpetuate the false idea that it 

 is an effect of altitude. In the remarks that follow, less promin- 

 ence will be given to the heights which were reached than to the 

 pressures which were experienced ; though, as it is more usual 

 to think in feet than in barometric inches, the approximately 

 equivalent elevations will be given with the pressures that are 

 mentioned. 



Notwithstanding the large number of allusions which had been 

 made in print to Mountain - sickness, I was unable, prior to my 

 journey amongst the Great Andes of the Equator, to tell at what 

 pressure it was probable that we might or should be affected. I 

 found, also, that I could not distinguish with certainty the effects 

 which were due to diminution in pressure from those which might 

 have arisen from other causes ; or, further, say which (if any) of 

 the effects that might be certainly due to diminution in pressure 

 would remain permanently if one should continue constantly at a 

 low pressure. These three points were those upon which I sought 

 for information. — Firstly, at wliat jiressure shall we commence to be 

 affected ? Secondly, in what way shall we be affected ? Thirdly, 

 can one become habituated to low j^^essures 9 



The answer to the first question came sooner than was ex- 

 pected. At a pressure of 16*500 inches (16,664 feet) we were 

 incapacitated for work [pp. 48-53], and found ourselves jn-e- 

 occupied by the paramount necessity of obtaining air. All pains 

 had been taken to eliminate the possibility of complications from 

 other causes, and I repeat [see p. 52] ^*^that our incapacity ^ at 

 this time was neither due to exhaustion nor to deficiency of bodily 

 strength, nor to weakness from want of food, but was caused by 

 the whole of our attention being taken up in efforts to get air.'^ 



