Page:Popular Science Monthly Volume 35.djvu/852

826 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 certain 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 considerable objection to speaking in this way if our purpose was simply to indicate a correspondence between our muscular sensations 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 disposable energy. The anticipatory sensation which we feel just as we are about to make a movement, and which we take for a consciousness of the force we are going to expend, is only a preconceived 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 explanations 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 cognizance 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