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 admiration 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 height from what it had been at 25,000 feet, or even lower; and I have no doubt there are many people, if only they can be found, who can get to the top of Everest unaided save by their own physiological reaction to a life at 21,000 feet for a few days. If a number of such people were allowed to live at a height corresponding to our Camp III for a fortnight or so, making perhaps a few minor excursions to 23,000 or 24,000 feet, then I have no doubt from the physiological point of view that they will be able to climb Mount Everest, provided the weather is fine and the wind not too violent. Without allowing time for acclimatisation to take place, it is