carbonic acid formed during great muscular effort is not the principal cause of the distress experienced. That gas is thrown off by increased expiration. It is the using up of the oxygen and the insufficiency of the supply in the atmospheric air inspired that causes, under these circumstances, giddiness, exhaustion, and often collapse. The difficulty in breathing and the prostration experienced by many people in mountain-climbing is largely due, not merely to the muscular effort of climbing, but to the fact that the rarefied atmosphere at heights of 8000 ft. to 15,000 ft. and more gives into the lungs in every inspiration but a fraction of the oxygen which is inspired at low levels, and moreover, owing to the low pressure, much less is held in the blood. Even when conveyed by mule, cog-rail, or balloon to these heights—and, therefore, without muscular exertion, sensitive people suffer severely from temporary “oxygen-starvation.” They as well as the laborious mountaineer could be saved from all such inconvenience by the use of a skilfully-constructed “traveller’s flask” of oxygen gas. The observations and experiments as to the possible use of pure oxygen by athletes suggest that we might all benefit by occasional if not frequent use of such an atmosphere. Indeed, there are some individuals—amongst others a well-known and distinguished actor—who before making some special effort, or even when feeling tired and unequal to their daily work, inhale under medical supervision a certain quantity of oxygen gas. It would certainly seem that since country air, sea air, and mountain air are useful and refreshing, an artificial supply of extra oxygen might be inhaled in London, either in one’s own house or in establishments provided for the purpose, with definite benefit to health, especially if the inhalation were combined with exercise.