...sitting in a closetlike aperture in one wall of the laboratory. The niche had a comfortable chair. Doc closed the door, which became an indistinguishable part of the laboratory wall, with a seemingly very heavy piece of apparatus in front of it. The niche was ventilated. (Birds of Death)

Doc's Truth Serum

The truth serum was a product of the bronze man's chemical genius. It had the magical effect of removing the conversational brakes from the consciousness of the person to whom it was administered. It numbed the patient's ability to consciously resist. (Bequest of Evil)

Doc's Anaesthetic Gas

Early in his strange career of righting wrongs and punishing evildoers, the bronze man had developed a gas. The gas was an anaesthetic, quick-acting, odorless, colorless, and produced a harmless unconsciousness. Ordinarily the bronze man carried it in thin-walled gas containers, liquefied, which would burst and disperse the stuff without too much commotion. (Birds of Death)