The Nature of Animal Life. 19 



the elemental bricks, but into simpler molecular forms, and 

 these again in later stages into yet simpler forms, which 

 are then got rid of or excreted from the body. Meanwhile 

 the destructive fall of the molecular edifice is accompanied 

 by the liberation of energy — as heat, maintaining the 

 warmth of the body; as visible or hidden movements, in 

 locomotion, for example, and the heart-beat; and some 

 times as electrical energy (in electric fishes) ; as light (in 

 phosphorescent animals and the glow-worm), or as sound. 

 It is this abundant liberation of energy, giving rise to 

 many and complex activities, which is one of the dis- 

 tinguishing features of animals as compared with plants. 



We have now, I trust, extended somewhat and rendered 

 somewhat more exact our common and familiar knowledge 

 of the nature of animal life. In the next chapter we will 

 endeavour to extend it still further by a consideration of 

 the process of life. 



