To determine whether it is humanly possible to climb to the summit of Mount Everest or what may be the chances of success in such an undertaking, other factors besides the mere mountaineering difficulties have to be considered. It is at least probable that the obstacles presented by this mountain could be overcome by any competent party if they met them in the Alps. But it is a very different matter to be confronted with such obstacles at elevations between 23,000 and 29,000 feet. We do not know that it is physiologically possible at such high altitudes for the human body to make the efforts required to lift itself up even on the simplest ground. The condition of the party of 1921 in September during the days of the Assault cannot be taken as evidence that the feat is impossible. The long periods spent in high camps and the tax of many exhausting expeditions had undoubtedly reduced the physical efficiency of Sahibs and coolies alike. The party of 1922, on the other hand, will presumably choose for their attempt a time when the climbers are at the top of their form and their powers will depend on the extent of their adaptability to the condition of high altitude. Nothing perhaps was so astonishing in the party of reconnaissance as the rapidity with which they became acclimatised and capable of great exertions between 18,000 and 21,000 feet. Where is the limit of this process? Will the multiplication of red corpuscles continue so that men may become acclimatised much higher? There is evidence enough to show that they may exist comfortably enough, eating and digesting hearty meals and retaining a feeling of vitality and energy up to 23,000 feet. It may be that, after two or three days quietly spent at this height, the body would sufficiently adjust itself to endure the still greater difference from normal atmospheric pressure 6,000 feet higher. At all events, a practical test can alone provide the proof in such a case. Experiments carried out in a laboratory by putting a man into a sealed chamber and reducing the pressure say to half an atmosphere, valuable as they may be when related to the experiences of airmen, can establish nothing for mountaineers; for they leave out of account the all-important physiological factor of acclimatisation. But in any case it is to be expected that efforts above 23,000 feet will be more exhausting than those at lower elevations; and it may well be that the nature of the ground will turn the scale against the climber. For him it is all important that he should be able to breathe regularly, the demand upon his lungs along the final arete cannot fail to be a terrible strain, and anything like a tussle up some steep obstacle which would interfere with the regularity of his breathing might prove to be an ordeal beyond his strength. As a way out of these difficulties of breathing, the use of oxygen has often been recommended and experiments were made by Dr. Kellas,[14] which will be continued in 1922.