826 THE POPULAR SCIENCE MONTHLY. 



obligation of taking " a constitutional " every evening. Even man 

 can do this only exceptionally. Our intelligence permits us to 

 satisfy these physiological exigencies in a more rational manner ; 

 but it does not give us notice of them. What would become of 

 the most reasonable being in the world if he had to depend upon 

 his reason to tell him what he needed ? A real necessity exists for 

 us to be warned by special sensations. 



We sometimes dispose of this explanation cheaply by speaking 

 as if we had direct knowledge of our strength- Nothing could be 

 more simple were this the case. Strength accumulates in us while 

 we are inactive, ending by giving us a painful sense of nervous 

 tension, which prompts us to expend our excessive energy in cer- 

 tain exercises. We go through these first as a relief ; then, our 

 reserve force having been exhausted, we feel our strength failing, 

 and the need of repose comes upon us. There would be no con- 

 siderable objection to speaking in this way if our purpose was 

 simply to indicate a correspondence between our muscular sensa- 

 tions and the dynamical state of our muscles. But we must take 

 care not to believe that there is the shadow of an explanation 

 in it. 



What is it that takes place in us during that period of repose 

 when we say that energy is accumulating in us ? Our muscles 

 are undergoing restoration, are getting into a condition to form 

 new chemical combinations. But I have no knowledge how much 

 force they can expend at a given moment ; it exists in them in a 

 purely virtual condition. I do not feel it any more than I feel the 

 expansive force of the powder contained in a certain flask, or the 

 heat that may be disengaged from a particular piece of charcoal. 

 We have not, therefore, any degree of consciousness of our dis- 

 posable energy. The anticipatory sensation which we feel just as 

 we are about to make a movement, and which we take for a con- 

 sciousness of the force we are going to expend, is only a precon- 

 ceived imagination of the sensation of effort that will accompany 

 the contraction. Even at the instant when the contraction is 

 effected our sensation of effort only indicates to us the extent of 

 the actual tension of our muscles. It answers so little to the real 

 expenditure of our energy, that it would be exactly the same if we 

 should stretch them in that way without performing any work. 

 We shall therefore have to give up these conventional explana- 

 tions and regard matters more closely. 



When we have continued still for a long time, we feel, first, a 

 great desire to move. Like all our appetites, the inclination to 

 move is recognized, even before any sensation can give us cog- 

 nizance of it, by the effect which it produces on the imagination. 

 In unconscious hunger or thirst, we think, not precisely that it 

 would be agreeable to drink or eat, but that some broiled chicken 



