So haunting were these formulae, and so frequently did he come upon them, that before the doctor knew it he was repeating them under his breath. Eventually, however, he felt he had secured all the papers he could digest to advantage for the present; hence resolved to examine no more till he could bring the sceptical alienists en masse for an ample and more systematic raid. He had still to find the hidden laboratory, so leaving his valise in the lighted room he emerged again into the black noisome corridor whose vaulting echoed ceaselessly with that dull and hideous whine.