im in amazement. "What are you doing?" Tiger
said.

"Filtering him," Dal said. "He's infected. He must have been exposed to
the plague somehow, maybe when our little Bruckian visitor came on board
the other day. And if it's a virus that's causing this plague, the virus
filter ought to hold it back and still let Fuzzy's molecular structure
through."

They watched and sure enough a bluish-pink fluid began moving down
through the porcelain filter, and dripping through the funnel into the
beaker below. Each drop coalesced in the beaker as it fell until Fuzzy's
whole body had been sucked through the filter and into the jar below. He
was still not quite his normal pink color, but as the filter went dry,
a pair of frightened shoe-button eyes appeared and he poked up a pair of
ears. Presently the fuzz began appearing on his body again.

And on the top of the filter lay a faint gray film. "Don't touch it!"
Dal said. "That's real poison." He slipped on a mask and gloves, and
scraped a bit of the film from the filter with a spatula. "I think we
have it," he said. "The virus that's causing the plague on this
planet."

CHAPTER 10

THE BOOMERANG CLUE

It was a virus, beyond doubt. The electron microscope told them that,
now that they had the substance isolated and could examine it. In the
culture tubes in the _Lancet_'s incubators, it would begin to grow
nicely, and then falter and die, but when guinea pigs were inoculated in
the ship's laboratory, the substance proved its virulence. The animals
injected with tiny bits of the substance grew sick within hours and very
quickly died.

The call to the Hospital Ship was canceled as the three doctors worked
in feverish excitement. Here at last was something they could grapple
with, something so common among the races of the galaxy that the doctors
felt certain that they could cope with it. Very few, if any, higher life
forms existed that did not have some sort of submicroscopic parasite
afflicting them. Bacterial infection was a threat on every inhabited
world, and the viruses--the tiniest of all submicroscopic
organisms--were the most difficult and dangerous of them all.

And yet virus plagues had been stopped before, and they could be stopped
again.

Jack radioed down to the planet's surface that the diagnosis had been
made; as soon as the proper medications could be prepared, the doctors
would land to begin treatment. There was a new flicker of hopefulness in
the Br