lves that took in
a lot of warm air and produced smaller amounts hot enough to boil water.

"I'll see you whenever I can," Jake said. "But mostly, you're going to
be somewhat isolated so they won't trace you. Let them think they goofed
with the shuttles and hit you and Chris. Anything you need?"

"Guinea pigs," Doc told him sarcastically. It was meant as a joke,
though a highly bitter one. Jake nodded and left them.

Doc opened the cots as Chris came in, not bothering to unpack the
equipment. "Hit the sack, Chris," he told her.

She looked at him doubtfully. "You almost said that the way you'd
address a human being, Dan. You're slipping. One of these days you'll
like me again."

"Maybe." He was too tired to argue. "I doubt it, though. Forget it and
get some sleep."

She watched him silently until he got up to turn out the light. Then she
sighed heavily. "Dan?"

"Yeah?"

"I never got a divorce. The publicity would have been bad. But anyway,
we're still married."

"That's nice." He swung to face her briefly. "And they found the radio
in the microscope. Better get to sleep, Chris."

"Oh." It was a quiet exclamation, barely audible. There was a sound that
might have been a sniffle if it had come from anyone else. Then she
rolled over. "All right, Dan. I still want to help you."

He cursed himself for a stupid fool for telling her. Fatigue was ruining
what judgment he had. From now on, he'd have to watch her every minute.
Or had she really seen the value of the research by now? She wasn't a
fool. It should have registered on even her stubborn mind. But he was
too sleepy to think about it.

She had breakfast ready in the morning. She made no comment on what had
been said during the night. Instead, she began discussing a way to keep
one of the organic antibiotics from splitting into simpler compounds
when they tried to switch it over to Mars-normal. They were both
hopelessly bad chemists and biologists, but there was no one else to do
the work.

Chris worked harder than ever during the day.

Just after sundown, Jake came in with a heavy box. He dropped it onto
the floor. "Mice!"

Doc ripped off the cover, exposing fine screening. There were at least
six dozen mice inside!

"Harkness found them," Jake explained. "A hormone extraction plant used
them for testing some of the products. Had them sent by regular
shipments from Earth. Getting them cost a couple of men, but Harkness
claims it's worth it. He's a g