"Betty, no one has ever had such an experience as this, seen such a sight, and lived to tell of it. It must be ravenous with hunger, shut up in its amber cell inside the black fluid. I--" A sharp, whistling hiss interrupted his speech. The reptile was puffing and swelling, and as it grew in bulk with the intake of the air, its enamel-like scales stood out like bosses on the great body. It spat forth a cloud of black, oily mist, and Marable came to himself at last. He raised his revolver and fired at the creature, sending shot after shot from the heavy revolver into the head. * * * * * Betty Young screamed as the reptile reared up and made a movement toward them. Marable and the girl retreated swiftly, as the beast thumped to the floor with a thud and started at them, advancing with a queer, crawling movement. It was between them and the door. Betty thrust her gun into Marable's hands, for his own was empty and he had hurled it at the monster. "Hurry! Run for your life!" ordered Marable, placing himself between Betty and the reptile. She would not leave him till he swerved to one side, going dangerously close to the beast and firing into its head. The rush of the flowing body stopped; it turned and pursued him, leaving the girl safe for the moment, but separated from Marable. Luckily, on the smooth marble it could not get an efficient grip with its clawlike arms. It was clumsy in its gait, and for a time the man eluded it. Betty Young, looking about for a weapon, calling for help at the top of her lungs, caught sight of a fireman's ax in a glass case on the wall. She ran over, smashed the glass with the small hammer, and took out the heavy ax. Shot after shot reverberated through the big laboratory as Marable tried to stop the monster. Betty, bravely closing in from the rear, saw Marable leaping from side to side as the brute struck viciously at him time and again. The creature had been emitting cloud after cloud of black fog, and the atmosphere, in spite of the open windows, was dim in its vicinity. Vaguely Betty heard shouts from the far hall, but all she could do was to call out in return and run toward the horror. * * * * * Marable, out of breath, had climbed to the top of an amber block. Betty, close by, saw the reptile rear its bulk up into the air, until it was high enough to strike the man. Before it could send forth its death-dealing fang to pin Marable to the block, however, Betty Young brought the ax down on its back with all her strength. There was a sickening thud as the sharp weapon sunk deep into the fleshy back. She struck again, and the creature fell in folds, like a collapsing spring. It lashed back at her, but she leaped clear as it slashed in agony, thrashing about so that the whole room seemed to rock.