THE PLEASURE OF MOTION. 825 



If the same pain recurs frequently, the animal soon remarks 

 that some among these vague movements will contribute more 

 directly than others to assuage it, and will give the preference to 

 them. The habit of resisting a particular suffering by a special 

 movement, becoming hereditary, forms a veritable instinct. In 

 conformity with the general laws of evolution, there is established 

 a selection between injurious and useful reflex actions, and the 

 latter will gradually predominate. 



Even when we are not suffering from any accidental uneasi- 

 ness provocative of special muscular reaction, we are impelled to 

 move by the simple need of motion. Every animal has to expend 

 daily a more or less considerable sum of energy to procure food 

 for itself. The oyster, fixed on its rock, imbibes, without effort 

 and almost passively, the vegetable matter which the waves bring 

 to it. A snail, drawing itself slowly along on its belly, easily 

 reaches the leaves which are in its way. The ox marches, step by 

 step, in the field for hours, feeding upon the grass-leaves with 

 which its lips come in contact. A wolf has to make journeys 

 of leagues every day in search of its prey. The swallow has to 

 keep in incessant motion to procure enough insects to satisfy 

 its appetite. To the necessity for eating is added that of escap- 

 ing enemies, and this exacts an increase of activity from the 

 animal. Thus, each one, according to its kind, is obliged to be 

 in motion more or less every day, and is organized for it. If, 

 through accidental circumstances, its activity ceases to be useful, 

 it is nevertheless obligatory upon it, for its physical constitution, 

 having become adapted by heredity to the normal life of the spe- 

 cies, can not abruptly bend itself to other conditions of existence. 

 Its organism continues to furnish it the same quantity of energy, 

 which it has to expend in some way. Hence the movements 

 of the captive animals — of the lion which paces its cage, and of 

 the canary-bird that leaps from bar to bar. Hence the physi- 

 cal exercises with which persons whose occupation condemns 

 them to a too sedentary life relax themselves. This necessity 

 for motion is especially great in youth, because the young 

 animal must train itself in all the movements it will have to per- 

 form at a later age, and must also exercise its muscles and joints 

 to develop them. Thus every animal has a tendency daily to ex- 

 pend a certain quantity of force, which is determined, not by the 

 accidental wants of the individual, but by the general wants of 

 the species. 



How is this expenditure regulated ? By what criterion do we 

 know when we need exercise ? A matter so indispensable to the 

 good working of our organization can not be the product of reflex 

 action. It is evident that animals can not take exercise by rule, 

 after the manner of a gentleman who imposes upon himself the 



