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 good 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.