The action of ordinary oxygen gas is a separate matter. The atmosphere which we breathe consists of one part by volume of this gas and of four parts of nitrogen gas. It is the oxygen which is necessary to us and to all animals, and the nitrogen is merely an inert diluting accompaniment of the essential oxygen gas. It is, of course, easy to increase or to diminish the proportion of oxygen in the air breathed accordingly as one introduces additional pure oxygen or, on the other hand, diluting nitrogen into a collapsible bag or sac from which one continuously draws breath. Such a bag can be connected by a tube to a helmet or mask enveloping the head. The expired air is discharged by a specially provided passage. It used to be thought that it was dangerous to breathe pure undiluted oxygen, although the proportion of oxygen to nitrogen in the air taken into the lungs might be increased to as much as a half without injury, and, indeed, with great benefit in some serious conditions of collapse. Dr. Leonard Hill, F.R.S., of the London Hospital Medical College, has, however, recently shown that oxygen gas, of 97 per cent. purity, may be breathed continuously for as much as two hours without any ill-effects or sense of inconvenience. Contrary to what has been stated, it is neither exciting nor unpleasant. He has made the experiment on himself and on some of his assistants, and in doing so has made use of such an apparatus as that above-mentioned—so as to ensure the in-take of undiluted oxygen.
Dr. Hill and Mr. Martin Flack have further found that the exhaustion and labouring of the heart which is brought on by such special exertion as that involved in running a hundred yards race or a quarter-mile race, is almost completely avoided if the runner “fills his lungs” with oxygen gas before starting. The runner takes the oxygen gas into the lungs for some two or three minutes before starting to race; of course, the lungs are not thus actually “filled” with oxygen, but a much larger proportion of that gas is lodged in them than when ordinary air is breathed, and a full supply is thus afforded to the blood. The “distress” caused by violent athletic efforts appears to be entirely due to the using up of the available oxygen by the unusual activity of the muscles. The heart itself suffers most, the breathing becomes laboured, and there is a sense of suffocation, due simply to the urgent demand by the blood, heart and muscles for more oxygen. If, therefore, we ensure that there is an extra supply of pure oxygen in the lungs before the unusual effort is made, we avert these distressing symptoms: the unusual quantity of oxygen needed is ready for use. Dr. Hill himself and young men who have tried the plan of inspiration of oxygen before a foot-race, declare that they cannot believe that they are really running hard, even when surpassing their usual performance. They come in at the end of the quarter-mile, having beaten their record; and with no sense of having made a special effort; they feel fresh and ready to start again after more oxygen and a short rest. Moreover, the after-effect on the muscles is stated to be such that “stiffness” and what is called “grogginess” (due in ordinary circumstances to the retention of lactic acid in the muscle) do not supervene.