"Smathers, what makes him different?"

"How do I know?" growled Dr. Smathers, still peering. "There's something different about him, that's all."

Petrelli forcibly restrained his temper. "Very funny," he snapped.

"Not funny at all," Smathers snapped back. "No two human beings are identical--you know that." He lifted his gaze from the eyepiece of the instrument and settled in on the chemist. "He's got AB blood type, for one thing, which none of the volunteers had. Is that what makes him immune to whatever poison is in those things? I don't know.

"Were the other three allergic to some protein substance in the fruit, while MacNeil isn't? I don't know.

"Do his digestive processes destroy the poison? I don't know.

"It's got something to do with his blood, I think, but I can't even be sure of that. The leucocytes are a little high, the red cell count is a little low, the hemoglobin shows a little high on the colorimeter, but none of 'em seems enough to do any harm.

"It might be an enzyme that destroys the ability of the cells to utilize oxygen. It might be _anything_!"

His eyes narrowed then, as he looked at the chemist. "After all, why haven't you isolated the stuff from the fruit?"

"There's no clue as to what to look for," said Petrelli, somewhat less bitingly. "The poison might be present in microscopic amounts. Do you know how much botulin toxin it takes to kill a man? A fraction of a milligram!"

Smathers looked as though he were about to quote the minimum dosage, so Petrelli charged on: "If you think anyone could isolate an unknown organic compound out of a--"

"Gentlemen! _Please!_" said Dr. Pilar sharply. "I realize that this is a strain, but bickering won't help. What about your latest tests on MacNeil, Dr. Smathers?"

"As far as I can tell, he's in fine health. And I can't understand why,"

said the physician in a restrained voice.

Pilar tapped one of the report sheets. "You mean the vitamins?"

"I mean the vitamins," said Smathers. "According to Dr. Petrelli, the fruits contain neither A nor B_1. After living solely on them for four weeks now, he should be beginning to show some deficiencies--but he's not.

"No signs?" queried Dr. Pilar. "No symptoms?"

"No signs--at least no abnormal ones. He's not getting enough protein, but, then, none of us is." He made a bitter face. "But he has plenty of symptoms."

Dr. Petrelli raised a thin eyebrow. "What's the difference between a sign and a symptom?"

"A sign," said Smathers testily, "is something that can be objectively checked by another person than the patient. Lesions, swellings, inflammations, erratic heartbeat, and so on. A symptom is a subjective feeling of the patient, like aches, pains, nausea, dizziness, or spots before the eyes.

"And MacNeil is beginning to get all kinds of symptoms. Trouble is, he's got a record of hypochondria, and I can't tell which of the symptoms are psychosomatic and which, if any, might be caused by the fruit."

"The trouble is," said Petrelli, "that we have an unidentifiable disease caused by an unidentifiable agent which is checked by an unidentifiable something in MacNeil. And we have neither the time nor the equipment to find out. This is a job that a fully equipped research lab might take a couple of years to solve."

"We can keep trying," said Pilar, "and hope we stumble across it by accident."

[Ill.u.s.tration]

Petrelli nodded and picked up the beaker he'd been heating over an electric plate. He added a chelating agent which, if there were any nickel present, would sequester the nickel ions and bring them out of solution as a brick-red precipitate.

Smathers scowled and bent over his microscope to count more leucocytes.

Pilar pushed his notes aside and went over to check his agar plates in the constant-temperature box.

The technicians who had been listening to the conversation with ears wide open went back to their various duties.

And all of them tried in vain to fight down the hunger pangs that were corroding at their insides.

Broderick MacNeil lay in his bed and felt pleasantly ill. He treasured each one of his various symptoms; each pain and ache was just right. He hadn't been so comfortable in years. It really felt fine to have all those doctors fussing over him. They got snappy and irritable once in a while, but then, all them brainy people had a tendency to do that. He wondered how the rest of the boys were doing on their diet of banana-pears. Too bad they weren't getting any special treatment.

MacNeil had decided just that morning that he'd leave the whole state of his health in the hands of the doctors. No need for a fellow to dose himself when there were three medics on the job, was there? If he needed anything, they'd give it to him, so he'd decided to take no medicine.

A delightful, dulling la.s.situde was creeping over him.

"MacNeil! _MacNeil!_ Wake up, MacNeil!"

The s.p.a.ceman vaguely heard the voice, and tried to respond, but a sudden dizziness overtook him. His stomach felt as though it were going to come loose from his interior.

"I'm sick," he said weakly. Then, with a terrible realization, "I'm really _awful_ sick!"

He saw Dr. Smathers' face swimming above him and tried to lift himself from the bed. "Shoulda taken pills," he said through the haze that was beginning to fold over him again. "Locker box." And then he was unconscious again.

Dr. Smathers looked at him bleakly. The same thing was killing MacNeil as had killed the others. It had taken longer--much longer. But it had come.

And then the meaning of the s.p.a.ceman's mumbled words came to him. Pills?

Locker box?

He grabbed the unconscious man's right hand and shoved his right thumb up against the sensor plate in the front of the metal box next to the bed. He could have gotten the master key from Colonel Fennister, but he hadn't the time.

The box door dilated open, and Dr. Smathers looked inside.

When he came across the bottles, he swore under his breath, then flung the s.p.a.ceman's arm down and ran from the room.

"That's where he was getting his vitamins, then," said Dr. Pilar as he looked over the a.s.sortment of bottles that he and Smathers had taken from the locker box. "Look at 'em. He's got almost as many pills as you have." He looked up at the physician. "Do you suppose it was just vitamins that kept him going?"

"I don't know," said Smathers. "I've given him ma.s.sive doses of every one of the vitamins--from my own supplies, naturally. He may rally round, if that's what it was. But why would he suddenly be affected by the stuff _now_?"

"Maybe he quit taking them?" Pilar made it half a question.

"It's possible," agreed Smathers. "A hypochondriac will sometimes leave off dosing himself if there's a doctor around to do it for him. As long as the subconscious need is filled, he's happy." But he was shaking his head.

"What's the matter?" Pilar asked.

Smathers pointed at the bottles. "Some of those are mislabeled. They all say vitamins of one kind or another on the label, but the tablets inside aren't all vitamins. MacNeil's been giving himself all kinds of things."