in.] THE MEANING OF EVOLUTION 253 



the auxiliary elements that pass on to motor elements 

 the energy to expend; the animal moves as a whole, and, 

 as a whole also, procures energy by means of the organic 

 substances it assimilates. Thus, whether low or high in 

 the animal scale, we always find that animal life consists 

 (1) in procuring a provision of energy; (2) in expending it, 

 by means of a matter as supple as possible, in directions 

 variable and unforeseen. 



Now, whence comes the energy? From the ingested 

 food, for food is a kind of explosive, which needs only 

 the spark to discharge the energy it stores. Who has 

 made this explosive? The food may be the flesh of an 

 animal nourished on animals and so on; but, in the end 

 it is to the vegetable we always come back. Vegetables 

 alone gather in the solar energy, and the animals do but 

 borrow it from them, either directly or by some passing 

 it on to others. How then has the plant stored up this 

 energy? Chiefly by the chlorophyllian function, a chem- 

 icism sui generis of which we do not possess the key, and 

 which is probably unlike that of our laboratories. The 

 process consists in using solar energy to fix the carbon 

 of carbonic acid, and thereby to store this energy as we 

 should store that of a water-carrier by employing him to 

 fill an elevated reservoir: the water, once brought up, can 

 set in motion a mill or a turbine, as we will and when we 

 will. Each atom of carbon fixed represents something 

 like the elevation of the weight of water, or like the stretch- 

 ing of an elastic thread uniting the carbon to the oxygen 

 in the carbonic acid. The elastic is relaxed, the weight 

 falls back again, in short the energy held in reserve is 

 restored, when, by a simple release, the carbon is per- 

 mitted to rejoin its oxygen. 



So that all life, animal and vegetable, seems in its essence 

 like an effort to accumulate energy and then to let it 



