It was not too far from the truth to call it a form of cancer. The compound seemed to be as close as Jupiter came to an indigenous form of life. It grew, fed, reproduced itself, and showed something of the characteristic structure of an Earthly virus, such as tobacco mosaic, Of course it grew from outside by accretion like any nonliving crystal, rather than from the inside, by intussusception, like a cell; but viruses grew that way too, at least in vitro.

It was no stuff to hold up the piers of humanity's greatest engineering project, that much was sure. Perhaps it was a suitable ground substance for the ribs of some Jovian jellyfish; but in a Bridge caisson, it was cancer.

There was a scraper mechanism working on the edge of the lesion, flaking away the shearing arninos and laying down new ice. In the meantime, the decay in the caisson face was working deeper. The scraper could not possibly get at the core of the trouble which was not the calcium carbide dust, with which the atmosphere was charged beyond redemption, but was instead one imbedded speck of metallic sodium which was taking no part in the reaction fast enough to extirpate it. It could barely keep pace with the surface spread of the disease.

And laying new ice over the surface of the wound was worthless, as Eva should have known. At this rate, the whole caisson would slough away and melt like butter, within an hour, under the weight of the Bridge above it.

Helmuth sent the futile scraper aloft. Drill for the speck of metal? No it was far too deeply buried already; and its location was unknown.

Quickly he called two borers up from the shoals below, where constant blasting was taking the foundation of the caisson deeper and deeper into Jupiter's dubious "soil." He drove both blind, firesnouted machines down into the lesion.

The bottom of that sore turned out to be a hundred feet within the immense block of ice. Helmuth pushed the red button all the same.

The borers blew up, with a heavy, quite invisible 'blast, as they had been designed to do. A pit appeared on the face of the caisson.

The nearest truss bent upward in the wind; It fluttered for a moment, trying to resist. It bent farther.

Deprived of its major attachment, it tore free suddenly, and went whirling away into the blackness. A sudden flash of lightning picked it out for a moment, and Helmuth saw it dwindling like a bat with torn wings being borne away by a cyclone.

The scraper scuttled down into the pit and began to fill it with ice from the bottom. Helmuth ordered down a new truss and a squad of scaffolder. Damage of this order of magnitude took time to repair. He watched the tornado tearing ragged chunks from the edges of the pit until he was sure that the catalysis cancer had been stopped. Then suddenly, prematurely, dismally tired he took off the helmet.