pressure, breathes air that holds only one-half the normal proportion of oxygen. Consequently, he is subject to conditions of insufficient oxidation, and threatened with asphyxia. Hence his rapid respiration, in the effort to introduce into the blood the oxygen which is lacking; hence, too, the accelerated palpitation of the heart, and nervous and muscular debility.
But if the traveler whose blood is thus impoverished keeps perfectly still, he will not suffer much, for it needs very little oxygen to support the body in the state of immobility. But if he stirs about, if he tries to lift the weight of his body by climbing, then he has need of more oxygen than is contained in the blood; and, as this is not to be had, the symptoms of mountain-sickness make their appearance, and the only hope of relief is in repose. This is the reason why aeronauts, who perform no work, experience "balloon-sickness" at a far greater elevation than mountain-climbers experience the symptoms to which they are liable.
The cooler the air, the earlier the appearance of the symptoms. When it is warm, the traveler needs only a small quantity of oxygen to keep up the bodily temperature. But, when the air is cold, the loss of bodily heat increases, and hence the need of a more intense calorific oxygenation. But how can this be attained if the blood does not contain enough oxygen? This is the reason why, as I have already stated, mountain-sickness makes its appearance much earlier in the Alps than in the Himalaya.
Compressed Air.—For thirty years, physicians, following the footsteps of Junod, Pravaz, and Tabarié, have made use of compressed air in the treatment of sundry diseases, and they have produced remarkable results in cases of anæmia, passive hæmorrhage, chronic bronchitis, and emphysematous asthma. This I merely note in passing. Among the physiological phenomena, all observers have noted a diminution in the number of the heart-beats and of the respirations, and an increased amplitude of the latter. Physicians commonly employ a pressure of only one-third or one-half of an atmosphere, while I have specially studied pressures of several atmospheres.
These great pressures have been employed in various industries for a few years past, but more especially in submarine diving and in sinking piers for bridges.
In submarine diving, the diver incloses his head in a metal helmet with glass eye-pieces. Into this helmet, by means of a pump, compressed air is driven with force sufficient to expel it again through special orifices. Thus there is established an equality of pressure between the water around the diver and the air he breathes, and this is the conditio sine qua non of his being able to live beneath the water. Lead-weighted shoes and a water-proof dress complete the outfit. Messrs. Rouquayrol and Denayrouse have made the diver independent of the lighter or vessel from which, prior to their improve-
