Suddenly Dr. Jarvis turned, and, carrying the head in one hand, holding it by the hair, he advanced toward Nick.  In his other hand the doctor held a knife which he had used in his ghastly work.

Nick had little hopes of escaping discovery.  Evidently it was the doctor’s intention to carry the head into the cellar, and the detective was concealed close by the stairs.

But Nick was not discovered.  Dr. Jarvis stalked by, within six feet of him, and looked neither to the right nor to the left.

Still bearing the head, he descended the stairs, and Nick crept after him.

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.