Potter sighed, thinking. How ignorant a man can become on a diet of managed history. He wondered then how his own diet had been adjusted and managed.

'Diderot was one of us,' Potter growled.

Svengaard stared at him, shocked to silence by the man's... blasphemy.

'It comes down to this,' Potter said. 'Nature doesn't like being meddled with.'

A chime sounded beneath Svengaard's desk.

'Security?' Potter asked.

'That's the all clear,' Svengaard said. 'They're ready for us now.'

'Central's Security hotshots are all in place,' Potter said. 'You will note that they didn't stoop to report to you or to me. They watch us too, you know.'

'I've... nothing to hide,' Svengaard said.

'Of course you haven't,' Potter said. He moved around the desk, threw an arm across Svengaard's shoulders. 'Come alongi It's time for us to put on the mask of Archeus. We're going to give form and organization to a living body. Veritable gods, we are.'

Svengaard felt himself still lost in confusion. 'What'll they do... to the Durants?' he asked.

'Do? Not a damn' thing - unless the Durants force it. The Durants won't even know they're being watched. But Central's little boys will know everything that goes on in that lounge. The Durants won't be able to belch without the gas being subjected to a full and complete analysis. Come along.'

But Svengaard held back. 'Doctor Potter,' he asked, 'what do you think introduced that arginine chain into the Durant morula?'

'I'm closer to you than you think,' Potter said. 'We're fighting... instability. We've upset the biological stability of the inheritance patterns with our false isomers and our enzyme adjustments and our meson beams. We've undermined the chemical stability of the molecules in the germ plasm. You're a doctor. Look at the enzyme prescriptions we all have to take - how profound the adjustment we have to make to stay alive. It wasn't always that way. And whatever set up that original stability is still in there fighting. That's what I think.' Three

THE cutting room nurses positioned the vat under the enzyme console, readied the tubes and the computer-feed-analysis board. They worked quietly, efficiently as Potter and Svengaard examined the gauges. The computer nurse racked her tapes and there came a brief whirring-clicking as she tested her board.

Potter felt himself filled with the wakeful anxiety that always came over him before surgery. He knew it would give way presently to the charged sureness of action, but he felt snappish at the moment. He glanced at the vat gauges. The Krebs cycle was holding at 86.9, a good sixty points above death level. The vat nurse came over, examined his breather mask. He checked his microphone, 'Mary had a little lamb, its fleece was black as hades - the surgeon took the credit for... a joke on all the ladies.'

He heard a distinct chuckle from the computer nurse, glanced at her, but she had her back to him and her face already hidden by hood and mask.

The vat nurse said, 'Microphone working. Doctor.'

He couldn't see her lips moving behind her mask, but her cheeks rippled as she spoke.

Svengaard flexed his fingers in their gloves, took a deep breath. It smelled faintly of ammonia. He wondered why Potter always joked with the nurses. It seemed demeaning, somehow.

Potter moved across to the vat. His sterile suit crinkled with a familiar snapping hiss as he walked. He glanced up at the wall screen, the replay monitor which showed approximately what the surgeon saw and which was the view watched by the parents. The screen presented him with a view of itself as he turned his forehead pickup lens toward it.

Damn' parents, he thought. They make me feel guilty... all of them.

He returned his attention to the crystal vat now bristling with instruments. The pump's churgling annoyed him.

Svengaard moved to the other side of the vat, waiting. The breather mask hid the lower half of his face, but his eyes appeared calm. He radiated a sense of steadiness, reliability.

How does he really feel? Potter wondered. And he reminded himself that in an emergency there wasn't a better cutting-room assistant than Sven.

'You can begin increasing the pyruvic acid,' Potter said.

Svengaard nodded, depressed the feeder key.

The computer nurse started her reels turning.

They watched the gauges as the Krebs cycle began rising -87.0... 87.3... 87.8... 88.5.... 89.4... 90.5... 91.9...

Now, Potter told himself, the irreversible movement of growth has started. Only death can stop it. Tell me when the Krebs cycle reaches one hundred and ten,' he said.

He swung the scope and micromanipulators into place, leaned into the rests. Will I see what Sven saw? he wondered. He knew it wasn't likely. The lightning from outside had never struck twice in the same place. It came. It did what no human hand could do. It went away.

Where? Potter wondered.

The inter-ribosomal gaps swam into focus. He scanned them, boosted amplification and went down into the DNA spirals. Yes - there was the situation Sven had described. The Durant Embryo was one of those that could cross over into the more-than-human land of Central... if the surgeon succeeded.

The confirmation left Potter oddly shaken. He shifted his attention to the mitochondrial structures, saw the evidence of the arginine intrusion. It squared precisely with Sven's description, Alpha-helices had begun firming up, revealing the telltale striations at the aneurin shifts. This one was going to resist the surgeon. This was going to be a tough one.

Potter straightened.

'Well?' Svengaard asked.

'Pretty much as you described it,' Potter said. 'A straightforward job.' That was for the watching parents.

He wondered then what Security was discovering about the Durants. Would this pair be loaded down with search and probe devices disguised as conventional artifacts? Possibly. But there were rumors of new techniques being introduced by the Parents Underground... and of Cyborgs moving out of the dark shadows which had hidden them for centuries - if there were Cyborgs at all. Potter was not convinced.

Svengaard spoke to the computer nurse, 'Start backing off the pyruvic.'

'Backing off pyruvic,' she said.

Potter swung his attention to the priority rack beside him, checked the presentation - in the first row the pyrimidines, nucleic acids and proteins, then aneurin, riboflavin, pyridoxin, pantothenic acid, folic acid, choline, inositol, sulfhydryl...

He cleared his throat, lining up his plan for the attack on the morula's defenses. 'I will attempt to find a pilot cell by masking the cysteine at a single locus,' he said. 'Stand by with sulfhydryl and prepare an intermediary tape for protein synthesis.'

'Ready for masking,' Svengaard said. He nodded to the computer nurse who racked the intermediary tape into position with a smooth sureness.

'Krebs cycle?' Potter asked.

'One hundred and ten coming up,' Svengaard said.

Silence.

'Mark,' Svengaard said.

Again, Potter bent to the scope. 'Begin the tape,' he said. Two minims of sulfhydryl.'

Slowly, Potter increased amplification, chose a cell for the masking. The momentary clouding of intrusion cleared away and he searched the surrounding cells for clues that mitosis would take off on his directed tangent. It was slow... slow.

He'd just begun and his hands already felt sweaty in their gloves.

'Stand by with adenosine triphosphate,' he said.

Svengaard presented the feeder tube in the micromanipula-tors, nodded to the vat nurse. ATP already. This was going to be a tough one.

'Begin one minim ATP,' Potter said.

Svengaard depressed the feeder key. The whirring of the computer tapes sounded overly loud.

Potter lifted his head momentarily, shook it. 'Wrong cell,' he said. 'We'll try another one. Same procedure.' Again, he leaned into the scope and the rests, moved the micromanipula- tors, pushing amplification up a notch at a time. Slowly, he traced his way down into the cellular mass. Gently... Gently... The scope itself could cause irreversible damage in here.

Ahhh, he thought, recognizing an active cell deep in the morula. Vat-statis had produced only a relative slowing in here. The cell was the scene of intense chemical activity. He recognized doubled base pairs strung on a convoluted helix of sugar phosphate as they passed his field of vision.

His beginning anxiety had passed and he felt the old sure-ness with the often repeated sensation that the morula was an ocean in which he swam, that the cellular interior was his natural habitat.

Two minims of sulfhydryl,' Potter said.

'Sulfhydryl, two minims,' Svengaard said. 'Standing by with ATP.'

'ATP,' Potter said, then, 'I'm going to inhibit the exchange reaction in the mitochondrial systems. Start oligomycin and azide.'

Svengaard proved his worth then by complying without hesitation. The only sign that he recognized the dangers in this procedure was a question, 'Shall I have an uncoupling agent ready?'

'Stand by with arsenate in number one,' Potter said.

'Krebs cycle going down,' the computer nurse said. 'Eighty-nine point four.'

'Intrusion effect,' Potter said. 'Give me point six minim of azide.'

Svengaard depressed the key.

'Point four minim oligomycin,' Potter said. 'Oligomycin, point four,' Svengaard said. Potter felt that he lived now only through his eyes on the microscope and his hands on the micromanipulators. His existence had moved into the morula, fused with it.

His eyes told him that peripheral mitosis had stopped... as it should under these ministrations. 'I think we have it,' he said. He planted a marker on the scope position, shifted focus and went down into the DNA spirals, seeking the hydroxyl deformity, the flaw that would produce a faulty heart valve. Now he was the artist, the master cutter - the pilot cell determined. Now he moved to reshape the delicate chemical factory of the inner structure.

'Prepare for the cut,' he said.

Svengaard armed the meson generator. 'Armed,' he said.

'Krebs cycle seventy-one,' the computer nurse said.

'First cut,' Potter said. He let off the single, aimed burst, watched the tumbling chaos that followed. The hydroxyl appendage vanished. Nucleotides reformed.

'Hemoprotein P-450,' Potter said. 'Stand by to reduce it with NADH.' He waited, studying the globular proteins that formed before him, watching for biologically active molecules. Now! Instinct and training combined to tell him the precise instant. 'Two and a half minims of P-450,' he said.

A corner of turmoil engaged a group of polypeptide chains m the heart of the cell.

'Reduce it,' Potter said.

Svengaard touched the NADH feeder key. He couldn't see what Potter saw, but the surgeon's forehead lens reproduced a slightly off-parallax view of the scope field. That plus Potter's instructions told of the slow spread of change in the cell.

'Krebs cycle fifty-eight,' the computer nurse said.

Second cut,' Potter said.

'Armed,' Svengaard said.

Potter searched out the myxedema-latent isovalthine, found it. 'Give me a tape on structure,' he said. 'S-(iso-propylcarboxy-methyl) cystein.'

Computer tape hissed through the reels, stopped, resumed at a slow, steady pace. The isovalthine comparison image appeared in the upper right quadrant of Potter's scope field.

He compared the structures, point for point, said. Tape off.' The comparison image vanished.

'Krebs cycle forty-seven,' the computer nurse said.

Potter took a deep, trembling breath. Another twenty-seven points and they'd be in the death range. The Durant embryo would succumb.

He swallowed, aimed off the meson burst.

Isovalthine tumbled apart.

'Ready with cycloserine,' Svengaard said.

Ahhh, good old Sven, Potter thought. You don't have to tell him every step of the way what to do.

'Comparison on D-4-aminoisoxazolidon-3,' Potter said.

The computer nurse readied the tape, said, 'Comparison ready.'

The comparison image appeared in Potter's view field. 'Check,' he said. The image vanished. 'One point eight minims.' He watched the interaction of the enzymic functional groups as Svengaard administered the cycloserine. The amino group showed a nice, open field of affinity. Transfer-RNA fitted readily into its niches.

'Krebs cycle thirty-eight point six,' the computer nurse said.

'We'll have to chance it. Potter thought. This embryo won't take more adjustment.

'Reduce vat stasis to half,' he said. 'Increase ATP. Give me micro-feed on ten minims of pyruvic acid.'

'Reducing stasis,' Svengaard said. And he thought. This will be close. He keyed the ATP and pyruvic acid feeders.

'Give me the Krebs cycle on the half point,' Potter said.

Thirty-five,' the nurse said. 'Thirty-four point five. Thirty-four. Thirty-three point five.' Her voice picked up speed with a shocked breathlessness: Thirty-three... thirty-two... thirty- one... thirty... twenty-nine...'

'Release all stasis,' Potter said. 'Present the full amino spectrum with activated histidine. Start pyridoxin - four point two minims.'

Svengaard's hands sped over the keys.

'Back-feed the protein tape,' Potter ordered. 'Give it the full DNA record on computer automatic.'

Tapes hissed through the reels.

'It's slowing,' Svengaard said.