Page:Popular Science Monthly Volume 15.djvu/796

 may have local exhaustion—as when the muscles of our arm are no longer able to hold out a heavy weight—or we may have general exhaustion, as in sleep; and we may have local restorations due to nutrition—as when our exhausted arm, after some interval of rest, is again able to sustain the weight—or we may have a general restoration due to nutrition, as in the effects of sleep.

I have now said enough about the physiology of nutrition to render quite clear what I mean by recreation depending on the physiological necessity for a frequent change of organic activity. For although in the case of some organs—such as most of the secreting organs—activity is pretty constant, owing to the constant expenditure of energy being just about balanced by the constant income, in the case of nerves and muscles this is not so; during the times when these organs are in activity their expenditure of energy is so vastly greater than their income during the same times, that they can only do their work by drawing upon the stores of energy which have been laid up by them during the comparatively long periods of their previous rest. Now. recreation applies only to nerve and muscle; and what it amounts to is simply this—a change of organic activity, having for its object the affording of time for the nutrition of exhausted portions of the body. A part of the body having become exhausted by work done, and yet the whole of the body not being exhausted so far as to require sleep, recreation is the affording of local sleep to the exhausted part by transferring the scene of activity from it to some other part. Be it observed that a certain amount of activity is necessary for the life and health of all the organs of the body; so it would not do for the community of organs as a whole that, when any one set become exhausted by their own activity, all the others should share in their time of rest, as in general sleep. But, by transferring the state of activity from organs already exhausted by work to organs which are ready nourished to perform work, recreation may be termed, as I have said, local sleep.

Thus we see that, in a physiological no less than in a psychological sense, the term re-creation is a singularly happy one; for we see that, as a matter of fact, the whole physiology of recreation consists merely of a re-building up, re-forming, or re-creation of tissues which have become partly broken down by the exhausting effects of work. So that in this physiological sense recreation is partial sleep, while sleep is universal recreation. And now we see why it is that the one essential principle of all recreation must be that of variety of organic activity; for variety of organic activity merely means the substitution of one set of organic activities for another, and consequently the successive affording of rest to bodily structures as they are successively exhausted. The undergraduate finds recreation in rowing because it gives his brain time to recover its exhausted energies, while the historian and the man of science find recreation in each other's labors