When I was a boy, I was fond of all kinds of games. I was a good tennis player, and in the country an incessant hunter and fisherman. When on the city streets we boys could not find any other game to play, we would get up on the roofs of the houses and throw clothes-pins and snow-balls at the "Dagoes" working in the nearby excavations; so we had the fine game of being chased by the "Dagoes," with the chance, real or imaginary, of having a knife stuck into us. But then, as I grew older, and became aware of the pain and misery of the world, I lost my interest in games, and for ten years or so I never played; I did nothing but study and write. So my health gave way, and I had the problem of restoring it, and I spent some twenty years wrestling with this problem, before I thoroughly convinced myself on the point that there can be no such thing as sound and permanent health without a certain amount of play. I don't think there is any kind of hard physical work I failed to try, in the course of my experiments. I rode horseback, and took long walks, and climbed mountains, and swam, and dug gardens, and chopped down whole groves of trees and cut them up and carried them to the fireplace. I have done this latter work for a whole winter in the country, several hours every day, and it has done my health no good to speak of; I have been ready for a breakdown at the end of it. The reason is that all the time I was doing these things with my body, I was going right on working my brain. While I was swimming or climbing a mountain or galloping on horseback, I was absorbed in the next chapter of the book I was writing, so that I literally did not know where I was. I would make up my mind that I would not think about my work, and would make desperate efforts not to do so; but it was like walking along the edge of a slippery ditch--sooner or later I was bound to fall in, and go floundering along, unable to get out again! And the same thing applies to all gymnastic work. I have experimented with a dozen different systems of exercises, and with all kinds of water treatments; I have used dumb-bells and Indian clubs and Swedish gymnastics, MacFadden's exercises in bed, and the Yogi breathing exercises, and more kinds of queer things than I can remember now; but for me there is only one solution of the problem, which is to have an antagonist. It may be a deer I am trying to shoot, or some trout I am trying to lure out of their holes; it may be some boys I am trying to beat at football or hockey, or it may be the game I know best and find most convenient, which is tennis. If it is tennis, then it has to be someone who can make me work as hard as I know how; for if it is someone I can beat easily, why, before I have been playing ten minutes, I am busily working out the next chapter of a book, or answering letters I have just got in the mail.