He had detected the morphine they had cleverly mixed with his water; and, after his drowsiness and weird dreams had convinced him of the plot, had turned the trick on it by secretly emptying this water out and by drinking only while in the shop, where he could draw water from the faucet.

The cell guards' intelligence had been too limited to make them inquire of the brush shop guards about his habits.

Also, Gabriel, had feigned stupefaction while in the cell.

Thus he had simulated the effects of the drug, and had really thrown his tormentors off the track.
For months and months they were convinced that they were weakening his will and destroying his mentality, while as a matter of fact his reasoning powers and determination never had been more keen.
By bathing as often as possible, by taking regular and carefully planned calisthenics, by reading the best books in the prison library, by attention to every rule of health within his means, and by allowing himself no vices, not even his pipe, Gabriel now was emerging from the Bastile of Capitalism in a condition of mind and body so little impaired that he knew a few weeks would entirely restore him.

The good conduct allowance, or "copper," which they had been forced to allow him for exemplary conduct, had cut ten months off his sentence.