Astounding Stories of Super-Science, August 1930

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!"