n ANIMAL LIFE 127 



movements from place to place. True, every animal 

 cell expends a good deal often the whole of the 

 energy at its disposal in keeping itself alive ; but the 

 organism as a whole tries to attract as much energy as 

 possible to those points where the locomotive move 

 ments are effected. So that where a nervous system 

 exists, with its complementary sense-organs and motor 

 apparatus, everything should happen as if the rest of 

 the body had, as its essential function, to prepare for 

 these and pass on to them, at the moment required, that 

 force which they are to liberate by a sort of explosion. 



The part played by food amongst the higher animals 

 is, indeed, extremely complex. In the first place it serves 

 to repair tissues, then it provides the animal with the 

 heat necessary to render it as independent as possible 

 of changes in external temperature. Thus it pre 

 serves, supports, and maintains the organism in which 

 the nervous system is set and on which the nervous 

 elements have to live. But these nervous elements 

 would have no reason for existence if the organism 

 did not pass to them, and especially to the muscles 

 they control, a certain energy to expend ; and it may 

 even be conjectured that there, in the main, is the 

 essential and ultimate destination of food. This does 

 not mean that the greater part of the food is used in this 

 work. A state may have to make enormous expendi 

 ture to secure the return of taxes, and the sum which 

 it will have to dispose of, after deducting the cost of 

 collection, will perhaps be very small : that sum is, none 

 the less, the reason for the tax and for all that has been 

 spent to obtain its return. So is it with the energy 

 which the animal demands of its food. 



Many facts seem to indicate that the nervous and 

 muscular elements stand in this relation towards the 



