ATMOSPHERIC PRESSURE AND LIFE. 325 



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 per- 

 fectly 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 foot- 

 steps of Junod, Pravaz, and Tabarie, have made use of compressed 

 air in the treatment of sundry diseases, and they have produced re- 

 markable results in cases of anaemia, passive hsemorrhage, chronic 

 bronchitis, and emphysematous asthma. This I merely note in pass- 

 ing. 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 em- 

 ploy 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 sink- 

 ing 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, com- 

 pressed air is driven with force sufficient to expel it again through 

 special orifices. Thus there is established an equality of pressure be- 

 tween 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 inde- 

 pendent of the lighter or vessel from which, prior to their improve- 



