The scientists gathered in the observatory the next day.

Cimon said, "Vernadsky tells me the data on air is still negative, and Rodriguez has discovered no air-borne pathogenic organism of any type."

There was a general air of dubiety over the last statement.

Novee said, "The settlement died of disease. I'll swear to that."

"Maybe so," said Rodriguez at once, "but can you explain how? It's impossible. I tell you that and I tell you. See here. Almost all Earth-type planets give birth to life and that life is always protein in nature and always either cellular or virus in organization. But that's all. There the resemblance ends.

"You laymen think it's all the same; Earth or any planet. Germs are germs and viruses are viruses. I tell you you don't understand the infinite possibilities for variation in the protein molecule. Even on Earth, every species has its own diseases. Some may spread over several species but there isn't one single pathogenic life form of any type on Earth that can attack all other species.

"You think that a virus or a bacterium developing independently for a billion yeans on another planet with different amino acids, different enzyme systems, a different scheme of metabolism altogether is just going to happen to find Homo sapiens succulent like a lollipop. I tell you it is childishness."

Novee, his physician's soul badly pierced at having been lumped under the phrase, "You laymen," was not disposed to let it go that easily, "Homo sapiens brings its own germs with it wherever it goes, Rod. Who's to say the virus of the common cold didn't mutate under some planetary influence into something that was suddenly deadly? Or influenza. Things like have happened even on Earth. The 2755 para-meas-"

"I know all about the 2755 para-measles epidemic," said Rodriguez, "and the 1918 influenza epidemic, and the Black Death, too. But when has it happened lately? Granted the settlement was a matter of a century and more ago-still that wasn't exactly pre-atomic times, either. They included doctors. They had supplies of antibiotics and for space' sake, they knew the techniques of antibody induction. They're simple enough. And there was the medical relief expedition, too."

Novee patted his round abdomen and said stubbornly, "The symptoms were those of a respiratory infection; dyspnea-"

"I know the list, but I tell you it wasn't a germ disease that got them. It couldn't be."

"What was it, then?"

"That's outside my professional competence. Talking from inside, I tell you it wasn't infection. Even mutant infection. It couldn't be. It mathematically couldn't be." He leaned heavily on the adverb.

There was a stir among his listeners as Mark Annuncio shoved his thin body forward into the space immediately before Rodriguez.

For the first time, he spoke at one of these gatherings.

"Mathematically?" he asked eagerly.

Sheffield followed after, his long body all elbows and knees as he made a path. He murmured "Sorry" half a dozen times.

Rodriguez, in an advanced stage of exasperation, thrust out his lower lip and said, "What do you want?"

Mark flinched. Less eagerly, he said, "You said you knew it wasn't infection mathematically. I was wondering how-mathematics..." He ran down.

Rodriguez said, "I have stated my professional opinion." He said it formally, stiltedly, then turned away. No man questioned another's professional opinion unless he was of the same specialty. Otherwise the implication, clearly enough, was that the specialist's experience and knowledge was sufficiently dubious to be brought into question by an outsider. Mark knew this, but then he was of the Mnemonic Service.

He tapped Rodriguez's shoulder, while the others standing about listened in stunned fascination, and said, "I know it's your professional opinion, but still I'd like to have it explained."

He didn't mean to sound peremptory. He was just stating a fact.

Rodriguez whirled. "You'd like to have it explained? Who the eternal Universe are you to ask me questions?"

Mark was startled at the other's vehemence, but Sheffield had reached him now, and he gained courage. With it, anger.

He disregarded Sheffield's quick whisper and said shrilly, "I'm Mark Annuncio of Mnemonic Service and I've asked you a question. I want your statement explained."

"It won't be explained. Sheffield, take this young nut out of here and tuck him into bed, will you? And keep him away from me after this. Damn young jackass." The last was a clearly heard aside.

Sheffield took Mark's wrist but it was wrenched out of his grasp. The young Mnemonic screamed, "You stupid non-compos. You-you moron. You forgettery on two feet. Sieve-mind. Let me go, Dr. Sheffield-You're no expert. You don't remember anything you've learned, and you haven't learned much in the first place. You're not a specialist; none of you-"

"For space' sake," cried Cimon, "take the young idiot out of here, Sheffield."

Sheffield, his long cheeks burning, stooped and lifted Mark bodily into the air. Holding him close, he made his way out of the room.

Tears squeezed out of Mark's eyes, and just outside the door, he managed to speak with difficulty. "Let me down. I want to hear-I want to hear what they say."

Sheffield said, "Don't go back in. Please, Mark."

"I won't. Don't worry. But-"

He didn't finish the but.