PHENOMENA AND CONDITIONS OF LIFE 33 



height without seriously endangering his life by the resultant 

 decrease in the air-pressure. We must, however, bear in mind 

 that the evidence on this point is far from conclusive, as in 

 addition to the diminished air-pressure there are other injurious 

 factors to be taken into account, as, for instance, the want of 

 oxygen and the lowered temperature. 



One of the most instructive ascents was the unfortunate 

 journey of the French aeronauts, Sivel, Croce-Spinelli and 

 Tissandier. They ascended from Paris on April 15, 1875, and 

 soon reached a height of 7,000 metres. On ascending higher, 

 according to Tissandier, the only survivor, they began to feel a 

 faintness which increased from second to second. Soon they were 

 unable to make the least movement, even speaking having become 

 impossible. The senses, however, remained acute and the mind 

 clear. Having passed a height of 8,000 metres, they lost conscious- 

 ness. When they had regained it they found that they were 

 drifting at an altitude of 7,000 metres. Again they threw out 

 ballast, again the balloon rose, and again these aeronauts lost con- 

 sciousness. When at last Tissandier had once more recovered 

 consciousness the balloon was floating at a height of 6,000 metres. 

 His two comrades were dead. 



Sixteen years later Berson and Siiring reached the greatest 

 height ever gained by man, 11,000 metres, the barometer showing 

 193 mm. This ascent confirmed the experience that if a certain 

 height is exceeded consciousness is lost and other functions are 

 seriously disturbed. 



Bert has shown that the maximum and minimum of pres- 

 sure, under which animals may safely live, is in a certain degree 

 dependent upon the volume of oxygen in the air. We know that 

 the atmosphere of the earth consists (apart from other com- 

 ponents) of 21 parts of oxygen and 78.06 of nitrogen. The 

 pressure exercised by this amount of air upon the earth surface 

 is called an atmosphere and has been calculated as being 1.033 

 kilogrammes to the square centimetre. It is generally constant for 

 all terrestrial animals and plants. But the researches of Bert and 

 others have shown that it is possible, even in the case of the 

 higher animals, to alter these conditions without disturbing the 

 vital activity. For instance, mammals, including man, can per- 

 manently exist in an atmosphere which contains only fourteen 

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