Although it is true that at high altitudes there is less oxygen to breathe, the body rapidly protects itself by increasing the number of red blood corpuscles. These red corpuscles are the carriers of oxygen from the air to the various parts of the body. An increased number of carriers means an increase of oxygen to the body. It is just possible, therefore, that anyone properly acclimatised to, say, 23,000 feet would be able to ascend the remaining 6,000 feet, to the summit of Mount Everest. Moreover, if oxygen could be continuously supplied to the climbers by adventitious aid there is little doubt that 29,000 feet could be reached. The physiological difficulties met with in ascending to high altitudes are doubtless of a very high order, but can to a certain extent be eliminated by ascending gradually, day after day, so as to allow the body to accommodate itself by degrees to the new surroundings. There are, however, other difficulties that must be reckoned with, such as intense cold and frequent high winds. In any engine where loss of heat occurs, there is a corresponding loss of available energy. A bitterly cold wind not only robs one of much heat, but lowers the vitality as well. At altitudes above 24,000 feet, the temperature is often arctic, and the thermometer may fall far below zero. On the other hand, the rays of the sun are intense. The ultra-violet rays, that are mostly cut off by the air at sea-level, are a real source of danger where there is only one-third of an atmosphere pressure, as in the case at the summit of Mount Everest. The mountaineer also encounters dangers in the Himalaya, on the same scale as the difficulties. A snow-slide on a British mountain or in the Alps is an avalanche; often in the Himalaya it becomes almost a convulsion of nature. The huge ice-fields and glaciers that hang on the upper slopes of the mountains, when let loose, have not hundreds of feet to fall, but thousands, and the wind that is thereby produced spreads with hurricane force over the glaciers below, on to which the main body of the avalanche has fallen. Sometimes even the broken debris will rush across a wide glacier. Rock falls also assume gigantic proportions in the Himalaya. But all these dangers can be largely avoided by the skilled mountaineer, and he can choose routes up a mountain where they are not likely to occur. Some risks, however, must be always run, but they can be reduced to a minimum.