The voices became inaudible then as the men passed on. Simms stood in his tracks undecidedly. Then a glimmer of flare lightning in the sodden sky illuminated that strange tower just ahead. Like a magnet it drew him forward with its power. Crouching low, he reached its cylindrical sides. He was groping for the entrance when his hands touched something soft and yielding. Chilled, he waited for a second lightning flare. It came, and it revealed the body of the third space-rat, Sterns. The man was dead. His eyes were bulging and streams of blood were issuing from either ear. Bewildered, yet careful not to disturb the body, Simms completed his circle of the tower and found the entrance. Inside he felt rather than saw a spiral staircase leading upward. With the utmost caution he began to climb. He was breathing hard when he reached the top. A door barred his way. Simms pushed it open and stood staring on the threshold. A bluish _radite_ lamp was suspended from the ceiling. Occupying a good half of the chamber was a huge parabolic horn, its small end converging on a platform upon which a circular disc slowly revolved. In the center of the disc was a rounded heap of yellow crystals. The left wall was taken up by a switchboard, with a series of dials staggered across a _corbite_ panel. At the right wall, facing the open end of the parabolic horn, was a large wire cage. Simms strode forward. The crystals on the revolving disc were _Deleon_ Salts. But what was the meaning of this other apparatus? He peered inside the cage and stared, incredulously. _Hudrites!_ The cage was filled with hundreds of the Venusian swamp insects. And then abruptly something clicked in his brain like a puzzle piece fitting into a slot. This chamber housed the mechanism that made the rejuvenation salts adaptable to the Kamalis. The secret was vibration, a bombardment of supersonic waves, causing a basic mutation of the crystals' molecular structure. The _Hudrites_ were the Venus equivalent of the Earth cricket. But where a cricket gave off vibrations of 8,000 a second, the frequency of a _Hudrite_ had never been measured. It was said to be more than two million cycles. The vibrations from these insects were picked up by the parabolic horn and a sensitive detector and stepped up by a cyclestat. When the sound waves struck the crystals, they responded to it at their frequency and by its vibrations gave rise to a varying voltage. The sound waves of the _Hudrites_ were thereby converted into electrical vibrations and these electrical waves amplified with the aid of vacuum tubes. The two were then united, and this bombardment of supersonic and electrical waves changed the structure of the _Deleon_ crystals. No doubt the Kamali Oligarchs had discovered through long experiment just how long a vibration exposure was necessary to make the salts potent and still not effect their mental powers. The process undoubtedly took months of Venus time.