12 ZOOLOGY 



seat of life, cannot carry on their functions except in 

 a special environment. From the standpoint of pure 

 physics, it becomes impossible to separate rigidly the 

 processes or displays of energy of the living material 

 from those going on in the immediately adjacent 

 medium ; indeed, the whole combination really dis- 

 plays the activities which we call vital. 



The fact that water, in a liquid state, is necessary 

 for the manifestation of vital activities, greatly re- 

 stricts the possibilities of life in the universe. If we 

 make a table of the known temperatures, from the cold 

 of space to that of the hottest stars, the portion of it 

 on which we mark water as liquid seems almost in- 

 finitesimal ; yet it is within these narrow limits that 

 the manifestations of life must occur. It is true, as 

 we have seen, that temperatures below the limit do 

 not necessarily injure the vital machine; but those 

 above the boiling point cause irreparable damage. 

 Gelation occurs which is irreversible, and the rhythm 

 of life has departed. 



The vital II. Life, then, is rhythmic; summer and winter, 



rhythm j a ^ an( j n ig ntj the rise and fall of each successive gen- 

 eration, the beating of the heart, the reversible states 

 of the living colloid, the dance of the atoms and elec- 

 trons, everywhere in nature we see the swinging pendu- 

 lum which marks the passage of time. No wonder that 

 music appeals to us irresistibly, and that in decorative 

 art beauty is gained by the repetition of a theme. 

 As Bergson insists, our deepest convictions arise out 

 of the very nature of life itself. 



