ing of lightning shamed the dull soggy twilight
produced by the large, hot, but hidden sun.

"_Your_ idea of a joke!" Forepaugh growled in disgust. He understood
what Gunga's grim pleasantry referred to. There was indeed an
incalculable quantity of hydrogen at hand. If some means could be
found to separate the hydrogen atoms from the oxygen in the world of
water around them they would not lack for fuel. He thought of
electrolysis, and relaxed with a sigh. There was no power. The
generators were dead, the air drier and cooler had ceased its rhythmic
pulsing nearly an hour ago. Their lights were gone, and the automatic
radio utterly useless.

"This is what comes of putting all your eggs in one basket," he
thought, and let his mind dwell vindictively on the engineers who had
designed the equipment on which his life depended.

An exclamation from Gunga startled him. The Martian was pointing to
the ventilator opening, the only part of this strange building that
was not hermetically sealed against the hostile life of Inra. A dark
rim had appeared at its margin, a loathsome, black-green rim that was
moving, spreading out. It crept over the metal walls like the
low-lying smoke of a fire, yet it was a solid. From it emanated a
strong, miasmatic odor.

"The giant mold!" Forepaugh cried. He rushed to his desk and took out
his flash pistol, quickly set the localizer so as to cover a large
area. When he turned he saw, to his horror, Gunga about to smash into
the mold with his ax. He sent the man spinning with a blow to the ear.

"Want to scatter it and start it growing in a half-dozen places?" he
snapped. "Here!"

* * * * *

He pulled the trigger. There was a light, spiteful "ping" and for an
instant a cone of white light stood out in the dim room like a solid
thing. Then it was gone, and with it was gone the black mold, leaving
a circular area of blistered paint on the wall and an acrid odor in
the air. Forepaugh leaped to the ventilating louver and closed it
tightly.

"It's going to be like this from now on," he remarked to the shaken
Gunga. "All these things wouldn't bother us as long as the machinery
kept the building dry and cool. They couldn't live in here. But it's
getting damp and hot. Look at the moisture condensing on the ceiling!"

Gunga gave a guttural cry of despair. "It knows, Boss; look!"

Through one of the round, heavily framed ports it could be seen, the
lower part of its