Our greatest enemy as we went on was not, after all, the deep powdery snow. The racket sank slightly below the surface and carried a little snow each step as one lifted it; the work was arduous for the first man. But at a slow pace it was possible to plod on without undue exhaustion. The heat was a different matter. In the glacier-furnace the thin mist became steam, it enveloped us with a clinging garment from which no escape was possible, and far from being protected by it from the sun's fierce heat, we seemed to be scorched all the more because of it. The atmosphere was enervating to the last degree; to halt even for a few minutes was to be almost overwhelmed by inertia, so difficult it seemed, once the machinery had stopped and lost momentum, to heave it into motion again. And yet we must go on in one direction or the other or else succumb to sheer lassitude and overpowering drowsiness. The final slopes, about 700 feet at a fairly steep angle, undoubtedly called for greater efforts than any hitherto required of us. The importance of breathing hard and deeply had impressed itself upon us again and again. I had come to think of my own practice as a very definite and conscious performance adopted to suit the occasion. The principles were always the same--to time the breathing regularly to fit the step, and to use not merely the upper part of the lungs, but the full capacity of the breathing apparatus, expanding and contracting not the chest only, but also the diaphragm, and this not occasionally but with every breath whenever the body was required to work at high pressure. Probably no one who has not tried it would guess how difficult it is to acquire an unconscious habit of deep breathing. It was easy enough to set the machine going in the right fashion; it was another task to keep it running. The moment attention to their performance was relaxed, the lungs too would begin to relax their efforts, and often I woke from some day-dream with a feeling of undue fatigue, to find the cause of my lassitude only in the lungs' laziness. The best chance of keeping them up to their work, I found, was to impose a rhythm primarily upon the lungs and swing the legs in time with it. The practice employed for walking uphill under normal conditions is exactly contrary, in that case the rhythm is consciously imposed on the legs and the rest of the body takes care of itself.