swear on a stack of Bibles

Why not check me into a sanatorium, let them watch me, examine me, give me the tests? In twelve hours they can tell whether I'm lying or not. If I'm clean, I'll be all right. If I'm not, I'll get sick as a dog, start throwing up at both ends, and this would prove I'm a damn liar. It would be better than all the affidavits in the world. I could swear on a stack of Bibles, but who would believe me? […] So I did it. It cost me almost a thousand dollars to pay the doctors to watch me and supervise me down to the last minute so they could go to court and make a statement. I stayed there four days; and when I left, everyone in the place was ready to swear on a stack of Bibles that I was clean.