"Run, boys; run for your lives!" shouted the professor. "There's something deadly in there!"
They needed no second invitation. Forward they plunged, gasping and choking, in the grip of the unseen, destructive agent they had liberated.
The professor, as he sprang forward, felt his foot slip, and realized that he was falling backward. As he fell into what he knew must be the pit they had opened, and from which the noxious fumes were pouring, he grasped at something—it was Walt's leg.
"Hey, leggo my leg!" howled the red-headed youth, half-crazy with fear. To his excited imagination, it seemed that in the darkness some pulling arm had reached up from the pit and seized him.
"Walt! Walt!" gasped the professor. "Save me!"
The boy, in agony as he was from the horrible gases, pluckily reached round and felt about. Presently he felt the professor's bony hand grip his. A second later, the scientist had been hauled out of danger. But the suffocating fumes still filled the passage. They were choking, blinding and killing the adventurers.
"Forward, forward! It's our only chance!" cried the professor.
Suddenly he felt Walt, who was just ahead of him in the panic-stricken flight, collapse. Seizing the fainting boy in his arms, the professor bravely struggled on. In the meantime Ralph had hastened on ahead, and knew nothing of what had occurred behind him.
Rapidly he ran from the unseen peril, covering the ground swiftly. Stumbling blindly forward, he all at once felt the air grow fresh and sweet, and at the same time a sort of glow penetrated the stygian darkness of the tunnel.
The boy glanced upward and gave a cry of delight. Above him, at the mouth of a circular shaft, he saw the kindly stars blinking. Never had the sight of the sky looked so sweet to him. But even as he was congratulating himself, he looked about for his companions.