ON NERVOUS ENERGY 59 



realisation of the value of exercise, but that their nervous 

 systems are irritable with energy which demands an 

 outlet. In the above cases the nervous energy will have 

 accumulated during the period of muscular inactivity. 

 And if the supply is not utilised it will gradually abate 

 and proportion itself to the amount used. 



Thus the same authority continues : " But it is very 

 necessary to yield promptly to the solicitations of this 

 instinct, for the sense of need for exercise tends very 

 soon to disappear if its satisfaction is delayed. If not 

 heeded, it lessens day by day ; if inaction is immoderately 

 prolonged, it disappears entirely, and the time arrives 

 when the organism which has too long led an inactive 

 life shows a marked tendency to become more and more 

 inactive. This is because too prolonged repose has 

 brought about new organic conditions, uniting as it does 

 all the circumstances which lead to the production of 

 every kind of fatigue." * 



Clearly, the disappearance of the sense of need for 

 exercise is due to the fact that the nerves are no longer 

 highly charged with energy. 



An abundance of facts could be quoted to show that 

 the amount of energy available is increased by exercise. 

 Different kinds of athletic exercises lead to the expenditure 

 of different amounts of nervous energy, and it is necessary 

 to train for them by different methods. Thus sprint- 

 running requires the expenditure of an enormous amount 

 of nervous energy in a very short time. But long-distance 

 running is rather a matter of muscular endurance. An 

 appreciable interval of time elapses between the nervous 

 discharge and the contraction of the muscle which follows, 

 and it was established by Helmholtz that the length of 

 the latent period is inversely proportional to the strength 

 1 Physiology of Bodily Exercise, Fernand Lagrange, part r, chap. i. 



