THE GENERAL CONDITIONS OF LIFE 293 



problem will require specialised methods, and the values for the 

 individual constituents of the air and the water, such as oxygen, 

 carbonic acid, etc., must be separatelj- determined manometrically. 



In discussing oxj-gen as a general condition of life, we became 

 acquainted with the importance of the partial pressure of this 

 gas,^ and learned that pure oxygen at a pressure of more than three 

 atmospheres is fatal to homothermal animals, while with ordinary 

 air the same result appears at a pressure of 15 — 20 atmospheres. 

 Death likewise follows when the partial pressure of the oxygen 

 falls too "low. 



The venturesome method of balloon-travel has been employed 

 to collect facts regarding the height at which the pressure of the 

 air becomes so small that danger to human life results. The 

 balloon trip that was made out of Paris in the year 1875, by 

 Spinelli, Sivel and Tissandier, has become famous. They rose 

 with considerable rapidity, and without any disturbance reached 

 a height of 7,000 metres. At about 7,500 metres, Tissandier 

 relates, they felt constantly increasing weakness and apathy, 

 which soon increased to complete absence of the power of motion, 

 although their minds still remained clear. They could no longer 

 perform voluntary movements, nor could they even use their 

 tongues for speaking. After Tissandier had made the observa- 

 tion that the balloon had passed a height of 8,000 metres, and 

 after vain efforts to communicate this fact to his two companions, 

 he lost consciousness. When he awoke, thej^ had descended to 

 7,059 metres. Then Spinelli, who also had awaked, threw out 

 sand in order that they should not fall too rapidly. As a result 

 of this the balloon again rose, and the aeronauts again lost con- 

 sciousness. When Tissandier awoke a second time they had sunk 

 to 6,000 metres, and the barometer showed that the balloon had 

 reached a height of about 8,500 metres. Spinelli and Sivel never 

 regained consciousness. 



The minimum of air-pressure under which plants and animals 

 can still remain alive can be determined by the air-pump. In such 

 an experiment the most important thing for animals is the partial 

 pressure of oxygen, for plants that of carbonic acid. 



As regards the water-pressure under which life can exist, far 

 fewer facts are known than as regards the pressure of the air. The 

 interesting deep-sea investigations i.if the last ten years have 

 shown, in opposition to earlier ideas, that living organisms exist 

 even in the greatest depths of the sea, where darkness always 

 prevails and bodies are subject to a pressure of several hundred 

 atmospheres. This pressure is so great that upon its sudden with- 

 drawal, as when the animals are drawn to the surface, they burst. 

 Fishes come up swollen, with their scales standing out and their 

 intestines protruding from their mouths (Fig. 132) ; this is observed 



1 Cf. p. 282. 



