It is, however, a certain fact that all individuals are not equally affected by diminished pressure, and that instances have occurred at such heights as 14–15,000 feet in which some persons have suffered whilst others have escaped, though the latter have not been exempt upon mounting to greater altitudes. But whilst this must be admitted; and also the probability that the effects of fatigue have often been wrongly interpreted; and, further, that personal frailties are frequently manifested upon mountain ascents, or at great elevations, there is a large residuum which cannot be explained away; and any one examining the matter can hardly fail to arrive at the conclusion that mountain-sickness is a world-wide reality.
This subject, long since, appeared to me to be worthy of investigation for its own sake, more particularly for ascertaining the heights at which effects begin to manifest themselves; the symptoms; and whether the effects are permanent. It seemed certain that, sooner or later, every one must be affected by diminished pressure, but the manner in which it would operate was uncertain, and whether its effects would be felt permanently at any given elevation was unknown. Those who have been affected by mountain-sickness have always desired to be rid of the infliction, and have descended to lower levels at the earliest opportunity. Hence it had not been ascertained whether cures might be effected on the spot; or, to put the matter in another way, whether one can become habituated to low pressures. The remarks which have fallen from those who are most entitled to attention have not been of an encouraging nature, and it may be inferred from their general tenor that as the cause is constant and permanent so will the effects be constant and permanent.
De Saussure, after finding himself through weakness, and difficulty in breathing, unable to make during a four and a half hours stay on the summit of Mont Blanc the experiments which he had repeatedly performed in less than three hours at the level of the
