The cellar was perfectly dark except where a faint glow around the little furnace could be perceived. Nick was therefore able to follow the doctor closely. But suddenly the place was made light. Dr. Jarvis had touched a button in the wall, and a row of electric lights, suspended before the furnace, flashed up. Nick had barely time to drop flat on the floor behind a row of great glass jars full of clear fluid, the nature of which he could not determine. These jars were set upon a sort of bench made of stone, rising about two feet from the floor. Between them and the furnace stood the doctor. Nick was on the other side. It seemed tolerably certain to the detective that Dr. Jarvis would throw the head into the furnace. Nick determined to get a sight of the head at once. He was yet uncertain whether it was Patrick Deever's. Rising on his hands and knees he peered between two of the jars. The head was not more than a yard from Nick's eyes, but the face was turned away. By the hair, and the general outline, it might be Deever's. At all hazards Nick must get a sight of it before it was consigned to the furnace in which a fire, supported by peculiar chemical agencies and much hotter than burning coal, raged furiously. Suddenly, when it seemed as if the doctor was about to raise an arch of fire-brick in order to throw the head into the fire, he turned and dropped the grim object into the jar almost directly above Nick's head. It was carefully done, though quickly. The head sank without a splash. Only a single drop of the fluid--a drop no bigger than a pin's point--fell upon the back of Nick's hand. It burned like white, hot iron. It seemed to sink through the hand upon which it fell. Nick sprang to his feet, not because of the pain of the burning acid, but because he knew that he must instantly obtain a sight of the head or it would be dissolved. It lay face upward in the jar, but the acid, even in that instant, had done its work. All semblance to humanity had vanished. As Nick gazed, the head seemed to waver in the midst of the strange fluid, and then, suddenly, Nick saw, in a direct line where it had been, the bottom of the jar. The head had been dissolved. Nick raised his eyes to Dr. Jarvis' face. There stood the doctor, entirely unmoved. He looked directly at Nick but seemed not to see him. His eyes were fixed, and their expression was peculiar. One less experienced than Nick would have supposed Dr. Jarvis to be insane. Certainly his conduct as well as his appearance seemed to justify such a conclusion. But Nick knew better. He recognized at once the peculiar condition in which Dr. Jarvis then was. He had seen the phenomenon before. "Walking in his sleep," Nick said to himself. "Shall I wake him here? I think not. Let me see what he will do." CHAPTER III. THE DOCTOR OFFERS A BRIBE. Nick was not greatly surprised by his discovery. He knew that Dr. Jarvis was a sleep-walker.