eathe. I could
hear him breathing in spite of all the noise of the battle."

"I noticed it," Arcot said. "He started breathing _before_ the fight
started. A human being can fight very swiftly, and with tremendous
vigor, for ten seconds, putting forth his best effort, and only breathe
once or twice. For another two minutes, he breathes more heavily than
usual. But after that, he can't just slow down back to normal. He has
used up the surplus oxygen in his system, and that has to be replaced;
he has run into 'oxygen debt'. He has to keep on breathing hard to get
back the oxygen surplus his body requires.

"But not Torlos! No fatigue for him! Why? _Because he doesn't use the
oxygen of the air to do work, and therefore his body is not a chemical
engine!_"

Morey nodded slowly. "I see what you're driving at. His body uses the
heat energy of the air! His muscles turn heat energy into motion the
same way our molecular beams do!"

"Exactly--he lives on heat!" Arcot said. "I've noticed that he seems
almost cold-blooded; his body is at the temperature of the room at all
times. In a sense, he is reptilian, but he's vastly more efficient and
greatly different than any reptile Earth ever knew. He eats food, all
right, but he only needs it to replace his body cells and to fuel his
brain."

"Oh, _brother_," said Morey softly. "No wonder he can do the things he
did! Why, he could have kept up that fight for hours without getting
tired! Fatigue is as unknown to him as cold weather. He'd only need
sleep to replace worn parts. His world is warm and upright on its axis,
so there are no seasons. He couldn't survive in the Arctic, but he's
obviously the ideal form of life for the tropics."

As the two men found out later, Morey was wrong on that last point. The
men of Torlos' race had a small organ, a mass of cells in the lower
abdomen which could absorb food from the bloodstream and oxidize it,
yielding heat, whenever the temperature of the blood dropped below a
certain point. Then they could live very comfortably in the Arctic
zones; they carried their own heaters. Their vast strength was limited
then, however, and they were forced to eat more and were more subject to
fatigue.

Wade and Fuller had been trying to speak with Torlos telepathically, and
had evidently run into difficulty, for Fuller called into the control
room: "Hey, Arcot, come here a minute! I thought telepathy was a
universal language, but this guy doesn't get our