. It's only killed five
children and three adults so far!"

"It would, here," Doc agreed unhappily. He led Chris out of the room on
the pretext of washing his hands. "It's serious enough to force us to
abandon the whole idea of going back to Earth-normal. Measles today,
smallpox, tuberculosis, scarlet fever and everything else tomorrow.
These people have lived Mars-normal so long their natural immunity has
been destroyed. On Earth where the disease was everywhere, kids used to
pick up some immunity with constant exposure, even without what might be
called a case of the disease. Here, the blood has no reason to build
antibodies. They can be killed by things people used to laugh at. How
the disease got here, I don't know. But it's here. So we'll have to
give up the idea of switching back to Earth-normal."

He gathered up one of the kits and started toward the other houses. "And
Lord knows how long it will take to get the blood for the other
treatment, even if it works."

They worked as a team for a while, with Harkness frowning as he watched
Chris. Finally the young doctor stopped Chris outside the fifth house.
"These are my patients, Dr. Ryan. I left the Lobby because I didn't
believe colonials were mere livestock. I still feel the same. I
appreciate your help in diagnosis and methods of treatment. But I can't
let you handle my patients this way."

"Dan!" She swung around with eyes glazing. "Dan, are you going to stand
for that?"

"I think you'd better wait in the tractor, Chris."

He was lucky enough to catch the kit she threw at him before its
precious contents spilled. But it wasn't luck that guided his hand to
the back of her skirt hard enough to leave it stinging.

Her face froze and she stormed out. A moment later they heard the
tractor start off.

But Doc had no time to think of her. He and Harkness split up and began
covering the streets, house by house, while he passed on the word to
abandon the metabolism switch and go back to Mars-normal.

Jake sent two other doctors to relieve them late in the evening. Things
were somewhat quieter at GHQ as Doc reported the events at Marconi.

"Where's Dr. Ryan?" Jake asked at last.

Doc exchanged glances with Harkness. "She isn't in the lab?"

"Wasn't there an hour ago."

Doc cursed himself for letting her go. With the knowledge that the radio
in the mike was disabled, she'd obviously grabbed the first chance to
report back. And with her had gone news of the