The Everest Expedition of 1922 had no preconceived programme of scientific investigation, and was first and foremost an attempt to get up the mountain; though, as I had been connected with physiological research for some years, I was naturally anxious to make observations on the effect of altitude on the human frame. These observations were rather subjective, and were unaccompanied by any accurate data—in other words, the reader will be relieved to hear that there are no tables of figures to be reproduced. Barcroft and others were in the course of their Expedition to the Andes, and I knew full well their results would supply more accurate information on the exact process of acclimatisation at high altitudes than anything we could do with our simpler apparatus. We left it to this other Expedition, therefore, to supply the figures, while our observations were exclusively on the practical side; that is to say, we observed the rapidity and effect of acclimatisation, while not investigating exactly how it is brought about. The first effect of altitude, in such moderate degree as we encountered it on the plains of Tibet, was almost 300entirely a mere breathlessness, which limited our rate of walking, and increased the popularity of our uncomfortable Tibetan saddles when travelling uphill. A few of us had severe headaches from time to time; at the modest height of 17,000 feet I noticed Cheyne-Stokes respiration at night when lying down, though never when sitting or standing; and I remember being distinctly amused at the fact that one was unable to control it.[7] A few of the party had a single attack of vomiting, but no permanent effect was noticed, and by the time we had lived on the Tibetan Plateau for a few weeks we had lost all ill effects save only breathlessness, which, of course, persisted to some extent until we reached comparatively low elevations. Further effect at these heights was not noticed save in the case of some of the older members of the party, who suffered from a considerable loss of appetite while at the Base Camp at 16,000 feet; this effect on appetite did not improve as time went on.
7.  For the benefit of the non-medical reader, Cheyne-Stokes breathing is the gradual alternation of shallow and deep respirations: usually about ten shallow breaths are followed by respirations which get gradually deeper; then by three or four really deep ones, which become shallower until the cycle recommences.
It was when we began the more serious work on the mountain that we made the most interesting observations on acclimatisation, and proved both its rapidity (which was known before) and its persistence to great heights. Scientists of various schools had, before the start of the Expedition, predicted that acclimatisation would be impossible 301above the height of 20,000 feet. Why they had done so will always remain a mystery to me; but possibly they were misled by the fact that so many climbing expeditions in the past have failed somewhere in the region of 23,000 feet above sea-level. We were enabled, however, to prove conclusively that acclimatisation does go on to greater heights; in fact, I do not see a theoretical limit to it at any elevation below the top of Mount Everest. Our observations were largely subjective, but for that reason they are perhaps all the more to be appreciated by the general reader; and in view of their subjective nature I may perhaps be pardoned in substituting “feelings” for figures and putting information in the form of a personal experience.
When Mallory and I arrived at Camp III and established it on the site chosen by the reconnaissance party, our first concern was the preparation of another camp at the North Col. I shall never forget our first ascent up that accursed slope of snow and ice, each step a hardship, every foot a fight; until at last we lay almost exhausted on the top. After a day or two at Camp III below, we went up again to the col, this time with Strutt and Morshead, and I think Norton. The ascent of the col this time was hard work, but not more than that; and after the col had been reached Morshead and I were sufficiently cheerful to explore the way leading up to Everest. A day or two later we again ascended the North Col, and never really noticed more discomfort than was occasioned by breathlessness. 302Though not possessing the scientific data which explained this change in our condition, yet in those few days of life at 21,000 feet we had become acclimatised to our altitude to a very remarkable degree; what had previously been a hard struggle had now become a comparatively easy job. By this rapid change in our constitution we had not only proved the predictions of scientists to be wrong, but had gained the physical power which took us without artificial oxygen supply to 27,000 feet, and we had determined that acclimatisation is not only possible but is also quite rapid at these high altitudes.
Thus, by sojourn and exercise for a week above 20,000 feet, we obtained the physiological equipment necessary for an attempt on the mountain, and at this point some personal experiences may be of interest, though possibly of no great importance. We found that, as we ascended, we fell into an automatic rate of breathing; Mallory preferred to breathe slowly and deeply, while rapid and shallower respirations appealed to me; but we all walked upwards at almost exactly the same rate at any given height. Below the North Col, I took three breaths to a step, while at 26,000 feet I was taking five complete respirations; but as long as I was walking slowly enough I experienced no distress or discomfort. If one hurried for a short distance, one was forced to rest for a few seconds—a rest was imperative, and one felt it were impossible to do without it; but as long as an even pace was kept up, one had no desire to stop, nor to make one’s 303admiration of the landscape an excuse for delaying one’s comrades. At the height of 26,000 feet, I took my pulse (which was 180) and my respirations (which were 50 to 55 to the minute); but withal one felt perfectly comfortable even though these abnormal physiological conditions were present. No doubt the heart must be young to stand this rate of beating for many hours; yet not too young, or it will easily become enlarged and permanently damaged.
In view of our experiences it seems justifiable to predict that acclimatisation at 23,000 feet will be sufficient for the attainment of the summit of Mount Everest, if indeed a sojourn at 21,000 feet is insufficient—which is to my mind more than doubtful. The other important practical observation we made is less encouraging: namely, that we all varied in our rate of acclimatisation, and in fact some of our number (especially the older ones among us) actually seemed to deteriorate in condition while staying at a great height. But I think we proved that it is possible to climb to the summit of Everest without the use of oxygen, though the selection of men who are able to do so is very difficult until those heights are actually reached at which acclimatisation becomes established. Personally I felt perfectly well at 27,000 feet, and my condition seemed no different at that he............