I occupied myself with these reflections, and found amusement in them; but it was impossible to lead Harry into a discussion.  His mind was anything but scientific, anyway; and he was completely obsessed by fear for the safety of Desiree.  And I wasn’t sorry for it; it is better that a man should worry about some one else than about himself.

Our chance of rescuing her, or even of saving ourselves, appeared to me woefully slim.  One fear at least was gone, for the descendants of Incas could scarcely be cannibals; but there are other fates equally final, if less distasteful.  The fact that they had not even taken the trouble to bind us was an indication of the strictness of their watch.

The hours crept by.  At regular intervals our food was replenished and we kept the platter empty, storing what we could not eat in our ponchos against a possible need.

It was always the same—­dried fish of the consistency of leather and a most aggressive taste.  I tried to convey to one of our captors the idea that a change of diet would be agreeable, but either he did not understand me or didn’t want to.

Gradually our strength returned, and with it hope.  Harry began to be impatient, urging action.  I was waiting for two things besides the return of strength; first, to lay in a supply of food that would be sufficient for many days in case we escaped, and second, to allow our eyes to accustom themselves better to the darkness.

Already we were able to see with a fair amount of clearness; we could easily distinguish the forms of those who came to bring us food and water when they were fifteen or twenty feet away.  But the cavern in which we were confined must have been a large one, for we were unable to see a wall in any direction, and we did not venture to explore for fear our captors would be moved to bind us.

But Harry became so insistent that I finally consented to a scouting expedition.  Caution seemed useless; if the darkness had eyes that beheld us, doubly so.  We strapped our ponchos, heavy with their food, to our backs, and set out at random across the cavern.

We went slowly, straining our eyes ahead and from side to side.  It was folly, of course, in the darkness—­like trying to beat a gambler at his own game.  But we moved on as noiselessly as possible.

Suddenly a wall loomed up before us not ten feet away.  I gave a tug at Harry’s arm, and he nodded.  We approached the wall, then turned to the right and proceeded parallel with it, watching for a break that would mean the way to freedom.

I noticed a dark line that extended along the base of the wall, reaching up its side to a height of about two feet and seemingly melting away into the ground.  At first I took it for a separate strata of rock, darker than that above.  But there was a strange brokenness about its appearance that made me consider it more carefully.

It appeared to be composed of curious knots and protuberances.  I stopped short, and, advancing a step or two toward the wall, gazed intently.  Then I saw that the dark line was not a part of the wall at all; and then—­well, then I laughed aloud in spite of myself.  The thing was too ludicrous.