A certain amount of breathing takes place viâ the pores of the skin. As, however, the best clothing for a climber on Mount Everest is windproof, there is a likelihood of the air surrounding the body becoming stale, in which case the process of skin-breathing is seriously impeded. This difficulty could be easily surmounted by flushing out the stale air by means of a tube inserted inside the climber’s clothes, the flushing-out process being done at intervals by temporarily fixing this tube to the orifice of the oxygen apparatus. It is not known definitely whether the advantage gained would be worth the trouble, but there is every reason for believing so. In any case it is a matter which might well be critically tested on the next Expedition. Cigarette-smoking proved of great value at high altitudes. Geoffrey Bruce, Tejbir, and I, after pitching camp at 25,500 feet, settled down inside our little tent about 2.30 in the afternoon. From then until seven o’clock the following evening we used no oxygen at all. At first we noticed that unless one kept one’s mind on the question of breathing—that is, made breathing a voluntary process instead of the involuntary process it ordinarily is—one suffered from lack of air and a consequent feeling of suffocation—a feeling from which one recovered by voluntarily forcing the lungs to work faster than they would of their own accord. There is a physiological explanation for this phenomenon. At normal altitudes human blood holds in solution a considerable quantity of carbon dioxide, which serves to stimulate the nerve centre controlling one’s involuntary breathing. At great altitudes, however, where, in order to obtain a sufficiency of oxygen, the climber is forced to breathe enormous volumes of air, much of this carbon dioxide is washed out of the blood, and the nerve centre, no longer sufficiently stimulated, fails to promote an adequately active involuntary breathing. A voluntary process must be substituted, and this throws a considerable strain upon the mind, and renders sleep impossible. On smoking cigarettes we discovered after the first few inhalations it was no longer necessary to concentrate on breathing, the process becoming once more an involuntary one. Evidently some constituent of cigarette smoke takes the place and performs the stimulating function of the carbon dioxide normally present. The effect of a cigarette lasted for about three hours. Clothing is a most important matter. It would be difficult to exaggerate the intensity of the cold encountered at high altitudes on Mount Everest. Several layers—the innermost of which should be of silk, the others wool of moderate weight—form a much better protection against cold than one or two heavy layers. The chief item of clothing, however, should consist of a jumper and trousers made of windproof material. Two of these windproof suits should be worn one above the other, and every precaution taken to reduce the circulation of the air to the smallest