1 8 Animal Life and Intelligence. 



source is solar radiance. This it is which gives the 

 succession of little pushes which keeps the pendulum of 

 life a-swinging. And it is the green plants which, through 

 their chlorophyll, are in the best position to utilize the 

 solar energy. They utilize it in building up, from the 

 necessary constituents diffused through the atmosphere 

 and the soil, complex forms of organic material, of which 

 the first visible product seems to be starch ; and these not 

 only contain large stores of potential energy, but are 

 capable, when combined with oxygen, of containing yet 

 larger stores. The animal, taking into its body these 

 complex materials, and elaborating them together with 

 oxygen into yet more complex and more unstable com- 

 pounds, then, during its vital activity, makes organized 

 use of the transformation of the potential energy thus 

 stored into lower forms of energy. Thus there go on side 

 by side, in both animals and plants, a building up or 

 synthesis of complex and unstable chemical compounds, 

 accompanied by a storage of potential energy, and a 

 breaking down or analysis of these compounds into lower 

 , and simpler forms, accompanied by a setting free of kinetic 

 energy. But in the plant, synthetic changes and storage 

 of energy are in excess, while in the animal, analytic 

 changes and the setting free of kinetic energy are more 

 marked. Hence the variety and volume of animal activities. 

 The building up of complex organic substances with 

 abundance of stored energy may be roughly likened to the 

 building up, by the child with his wooden bricks, of houses 

 and towers and pyramids. The more complex they become 

 the more unstable they are, until a touch will shatter the 

 edifice and liberate the stored-up energy of position 

 acquired by the bricks. Thus, under the influence of 

 solar energy, do plants build up their bricks of hydrogen, 

 carbon, and oxygen into complex molecular edifices. 

 Animals take advantage of the structures so elaborated, 

 modify them, add to them, and build yet more complex 

 molecular edifices. These, at the touch of the appropriate 

 stimulus, topple over and break down not, indeed, into 



