By sheer visualization under my eyelids I constructed chess-boards and played both sides of long games through to checkmate.  But when I had become expert at this visualized game of memory the exercise palled on me.  Exercise it was, for there could be no real contest when the same player played both sides.  I tried, and tried vainly, to split my personality into two personalities and to pit one against the other.  But ever I remained the one player, with no planned ruse or strategy on one side that the other side did not immediately apprehend.

And time was very heavy and very long.  I played games with flies, with ordinary house-flies that oozed into solitary as did the dim gray light; and learned that they possessed a sense of play.  For instance, lying on the cell floor, I established an arbitrary and imaginary line along the wall some three feet above the floor.  When they rested on the wall above this line they were left in peace.  The instant they lighted on the wall below the line I tried to catch them.  I was careful never to hurt them, and, in time, they knew as precisely as did I where ran the imaginary line.  When they desired to play, they lighted below the line, and often for an hour at a time a single fly would engage in the sport.  When it grew tired, it would come to rest on the safe territory above.

Of the dozen or more flies that lived with me, there was only one who did not care for the game.  He refused steadfastly to play, and, having learned the penalty of alighting below the line, very carefully avoided the unsafe territory.  That fly was a sullen, disgruntled creature.  As the convicts would say, it had a “grouch” against the world.  He never played with the other flies either.  He was strong and healthy, too; for I studied him long to find out.  His indisposition for play was temperamental, not physical.

Believe me, I knew all my flies.  It was surprising to me the multitude of differences I distinguished between them.  Oh, each was distinctly an individual—­not merely in size and markings, strength, and speed of flight, and in the manner and fancy of flight and play, of dodge and dart, of wheel and swiftly repeat or wheel and reverse, of touch and go on the danger wall, or of feint the touch and alight elsewhere within the zone.  They were likewise sharply differentiated in the minutest shades of mentality and temperament.

I knew the nervous ones, the phlegmatic ones.  There was a little undersized one that would fly into real rages, sometimes with me, sometimes with its fellows.  Have you ever seen a colt or a calf throw up its heels and dash madly about the pasture from sheer excess of vitality and spirits?  Well, there was one fly—­the keenest player of them all, by the way—­who, when it had alighted three or four times in rapid succession on my taboo wall and succeeded each time in eluding the velvet-careful swoop of my hand, would grow so excited and jubilant that it would dart around and around my head at top speed, wheeling, veering, reversing, and always keeping within the limits of the narrow circle in which it celebrated its triumph over me.