"What do you think, Dr. Allison?"

"There is no possible room for doubt." Jay Allison spoke precisely, in a rather high-pitched and emphatic tone. "It follows the statistical pattern for all recorded attacks of 48-year fever ... by the way, sir, haven't we any better name than that for this particular disease? The term '48-year fever' connotes a fever of 48 years duration, rather than a pandemic recurring every 48 years."

"A fever that lasted 48 years would be quite a fever," Dr. Forth said with the shadow of a grim smile. "Nevertheless that's the only name we have so far. Name it and you can have it. Allison's disease?"

Jay Allison greeted this pleasantry with a repressive frown. "As I understand it, the disease cycle seems to be connected somehow with the once-every-48-years conjunction of the four moons, which explains why the Darkovans are so superstitious about it. The moons have remarkably eccentric orbits—I don't know anything about that part, I'm quoting Dr. Moore. If there's an animal vector to the disease, we've never discovered it. The pattern runs like this; a few cases in the mountain districts, the next month a hundred-odd cases all over this part of the planet. Then it skips exactly three months without increase. The next upswing puts[89] the number of reported cases in the thousands, and three months after that, it reaches real pandemic proportions and decimates the entire human population of Darkover."

[89]

"That's about it," Forth admitted. They bent together over the folder, Jay Allison drawing back slightly to avoid touching the other man.

Forth said, "We Terrans have had a Trade compact on Darkover for a hundred and fifty-two years. The first outbreak of this 48-year fever killed all but a dozen men out of three hundred. The Darkovans were worse off than we were. The last outbreak wasn't quite so bad, but it was bad enough, I've heard. It has an 87 per cent mortality—for humans, that is. I understand the trailmen don't die of it."

"The Darkovans call it the trailmen's fever, Dr. Forth, because the trailmen are virtually immune to it. It remains in their midst as a mild ailment taken by children. When it breaks out into the virulent form every 48 years, most of the trailmen are already immune. I took the disease myself as a child—maybe you heard?"

Forth nodded. "You may be the only Terran ever to contract the disease and survive."

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