"It wasn't," said Kim.
"So," said Calhoun, "maybe it isn't one isolatable organism. Maybe the disease-producing mechanism simply isn't there when you make pure cultures of the separate strains of virus and microbe. Murgatroyd was a pretty sick animal. I've only known of one previous case in which a tormal reacted as violently as Murgatroyd did. That one had us sweating."
"If I were going to live," said Kim grimly, "I might ask what it was."
"Since you're going to," Calhoun told him, "I'll tell you though you don't. It was a pair of organisms. Their toxins acted synergically together. Separately they were innocuous. Together they were practically explosive. That one was the devil to track down!"
He went back across the glade. Murgatroyd came skipping after him, scratching at the anaesthetic patch on his hide, which he sometimes seemed to notice not because it felt oddly, but because it did not feel at all.
"You," said Calhoun briefly to Helen Jons, "you go first. This is an antibody serum. You may itch afterward, but I doubt it. Your arm, please."
She bared her rather pitifully thin arm. He gave her practically a CC of fluid which—plus blood-corpuscles and some forty-odd other essential substances—had been circulating in Murgatroyd's blood stream not long since. The blood-corpuscles had been clumped and removed by one compound plus the filter, and the anticoagulant had neatly modified most of the others. In a matter of minutes, the lab kit had prepared as usable a serum as any animal-using technique would produce. Logically, the antibodies it contained should be isolated and their chemical structure determined. They should be synthesized, and the synthetic antibody-complex administered to plague-victims. But Calhoun faced a small group of people doomed to die. He could only use his field kit to produce a small-scale miracle for them. He could not do a mass production job.
"Next!" said Calhoun. "Tell them what it's all about, Kim!"
The gaunt young man bared his own arm.
"If what he says is so, this will cure us. If it isn't so, nothing can do us any harm!"