ood man on a raid. Here!"

He'd gone to the doorway again and came back with another box, this one
crammed with bottles and boxes. "They had quite a laboratory, and
Harkness picked out whatever he thought you could use."

Chris and Doc were going through it. The labels were engineering ones,
but the chemical formulae were identification enough. There were dozens
of chemicals they hadn't hoped to get.

"Anything else?" Doc finally asked as they began arranging the supplies.

"More runners. A lot more. We're still holding things down, but it's
reaching a limit. Panic will start in the camps if this keeps on. But
that's my worry. You stick to yours."

Several of the new chemicals showed promise in the tubes. But two of
them proved fatal to the mice and the others were completely innocuous
in the little animal's bodies, both to mouse and to germ. The plague was
much hardier in contact with living cells than in the artificial
environment of the culture jars.

They lost seven mice in two days, but that seemed unimportant; the
females were already living up to their reputations, nearly all
pregnant. Doc didn't know the gestation period, but he remembered that
it was short.

"Funny they all started at the same time," he commented. "Must have been
shipped out separately or else been kept apart while they were switched
over to Mars-normal. Something interrupted their habits, anyhow."

A few nights later they learned what it was. There was a horrible
squealing that woke him out of the depths of his sleep. Chris was
already at the light switch. As light came on, they turned to the mouse
box.

All the animals were charging about in their limited space, their little
legs driving madly and their mouths open. What they lacked in size they
made up in numbers, and the din was terrific.

But it didn't last. One by one, the mice began dropping to the floor of
the cage. In fifteen minutes, they were all dead!

It was obviously the plague, contracted after having their metabolism
switched. Women were sterile for some time after Selznik's migraine
struck, and the same must have been true of the mice. They must have
contracted the plague at about the same time and reached fertility
together. Somehow, the plague incubation period had been shortened to
fit their life span; the disease was nothing if not adaptive.

Chris prepared a slide in dull silence. The familiar cell was there when
Doc looked through the microscope. He picked u