294 GENERAL PHYSIOLOGY 



even in the fishes that live in the depths of the Lake of Constance. 

 The height to which the pressure can rise before all life ceases 

 has thus far not been investigated. The diminution of the water- 

 pressure to the pressure of the atmosphere resting upon the water, 

 by means of an air-pump, appears to be without influence upon 

 organisms living in the water. But a great diminution of the 



FIG. 132. Ntoscopelus macrolepidotus, brought to the surface from a depth of 1500m. The eye 

 and the intestines are swollen out and the scales are falling off, owing to the great tension of 

 the skin over the body. (After Keller.) 



water-pressure is not possible without altering the liquid state of 

 the water. Here the question of the minimum of water-pressure 

 passes over into that of the minimum of air-pressure, and the 

 partial pressure of the contained gases, water- vapour, oxygen, etc., 

 and becomes connected with the questions of the importance of 

 moisture in the atmosphere, oxygen, etc., as general conditions of 

 life. 



B. THE GENERAL INTERNAL CONDITIONS OF LIFE 



The conditions, thus far spoken of, namely, a supply of food and 

 other substances, a definite degree of temperature, and a certain 

 pressure, comprise all the general conditions of life that must be 

 afforded by the medium. Others, such as light, are likewise 

 external but not general conditions, and pertain only to certain 

 organisms or groups of organisms. 



But along with the general external conditions there are 

 associated others that must be fulfilled also in order that life can 

 continue. These lie within the organism itself, and constitute the 

 general internal conditions of life. 



Obviously the chief requisite for the existence of life through 



