Our recent experiences having shown that the greatest altitude at which acclimatisation takes place is about 22,000 feet above sea-level, it may be reasonably assumed that, from the climber’s point of view, high altitude on Mount Everest begins at that height. Incidentally, also, on approaching the North Col over the East Rongbuk Glacier, the snow and ice conditions met with up to this level approximate very closely to summer conditions in the Alps. Above 22,000 feet, however, such conditions, particularly the state of the snow, resemble those met with in the Alps in mid-winter. This high-altitude zone may be further divided into two sub-zones—the first, from 22,000 feet (the foot of the steep snow and ice slopes leading up to the North Col) to 23,000 feet, in which climatic conditions are by no means severe, as the North Col affords protection from the prevailing west wind; and the second, from 23,000 feet onwards, of which extreme cold and strong wind are the predominant characteristics. It is therefore evident that the climber must be equipped according to the zone in which he finds himself. In the first zone clothing somewhat warmer than that 263used in the Alps in the summer is practically sufficient. Owing to the marked intensity of the sun’s rays, however, it is advisable to cover the trunk with at least one layer of sunproof material, such as a sunproof shirt with spine pad, while a solar topee and suitable snow-glasses constitute the best form of headgear. Crookes’ glasses of smoke-blue colour proved superior to other varieties; they afford complete protection from glare and do not cause eye-strain and subsequent headache. As sunburn, even very superficial and involving only a small area, is invariably followed by conditions of feverishness which must impair one’s fitness, a veil should be worn over the face and gloves on the hands. Oxygen should be employed from the foot of the North Col slopes onwards, for no useful purpose can be served by tiring oneself through not using it, when, as we have seen elsewhere, full recovery from fatigue is no longer possible at 23,000 feet. The second zone (from 23,000 feet onwards), where a radical change in climatic conditions is manifest, demands more complicated preparation. Wind is seldom absent, and the degree of intensity of the cold is comparable with that met with at the Poles, and indeed probably often exceeds it. Also, owing to the rarefied state of the atmosphere, the cold is felt much more severely than would be the case at sea-level. A far greater volume of air is expelled from the climber’s lungs, and this air, at blood heat and under a low pressure approximating to one-third of an atmosphere, is saturated with moisture drawn from the body via the 264lungs. The result is a proportionately far greater loss of animal heat. Further, the partial pressure of oxygen contained in a normal atmosphere becomes so low at altitudes over 23,000 feet that, unless the climber has recourse to a supply of oxygen carried by himself, his climbing efficiency is enormously reduced. The climbing equipment of the mountaineer in this second zone of high altitude should therefore include, firstly, a supply of oxygen; secondly, warm and windproof clothing and foot-gear; thirdly, plenty of food and drink, as the use of oxygen has a most stimulating effect upon the appetite.
The oxygen equipment has already been fully described by Mr. Unna in the Alpine Journal, vol. xxxiv., page 235. The apparatus is, in principle, quite simple. It consists of a frame carried on the shoulders of the climber, at whose back, in a rack attached to the frame, are four steel cylinders filled with oxygen compressed to 120 atmospheres. From the cylinders the oxygen is taken by means of copper tubes over to an instrument arm in front of the climber. This instrument arm, also attached to the frame, carries the pressure gauges and so forth which indicate how much oxygen the climber is left and how rapidly the supplies are being used up. Close to the instrument arm and readily accessible are the valves necessary for controlling the rate of flow of oxygen from the apparatus. From the instrument arm the oxygen passes through a flexible rubber tubing up to a mask covering the face of the climber. The two types of mask 265supplied to the Expedition proved useless, partly owing to their stifling effect upon the wearer, and partly to the fact that saliva and moisture collected rapidly under them and froze. Both, therefore, had to be discarded, but fortunately I was able to make a substitute which functioned successfully. This mask consists of a rubber tube into which is let a rubber bladder by means of a glass T-piece, or by means of two straight pieces of glass tube let in at opposite ends of the bladder. One end of the rubber tube is fastened to the tube of the apparatus out of which the oxygen flows, the other end being held in the climber’s mouth. On exhaling, the climber closes the rubber tube by biting upon it, and the oxygen issuing from the apparatus, instead of being wasted, is stored up in the rubber bladder. On inhaling, the pressure of the teeth is released sufficiently to allow the rubber tube to open, thus permitting the oxygen stored up in the bladder to flow into the climber’s mouth, whence, mixing with the air exhaled, it is drawn into the lungs. The chief advantages of this mask are that, firstly, it economises oxygen to the greatest possible extent, and secondly, the swelling and the shrinking of the bla............