I guess O.Henry is coining words. He is describing a man apparently with far advanced tuberculosis, and describes him as "debile". Not in dictionary, except as botanical epithet, meaning weak, feeble, etc.

"So, then, it was no surprise to the ranchhold when the buckboard spun to the door, and Raidler took up his debile protege like a handful of rags and set him down upon the gallery."