Dura, angry and unsettled, asked the doctor if Adda was healing.
“He’s doing as well as we could expect.”
“What’s that supposed to mean? Why can’t you people talk straight?”
The doctor’s smile thinned. “I mean that he’s going to live. And it looks as if his broken bones are knitting — slowly, because of his age, but knitting. And I’ve sewn up the ruptured vessels; most of his capillaries are capable of sustaining pressure now…”
“But?”
“He’s never going to be strong again. And he might not be able to leave the City.”
Dura frowned; brief, selfish thoughts of extended periods of fee-paying crossed her mind. “Why not? If he’s healing up as you say…”
“Yes, but he won’t be able to generate the same level of pneumatic pressure.” Maxx frowned quizzically. “Do you understand what that means?”
Dura gritted her teeth. “No.”
“Oh dear. It’s so easy to forget you’re all upfluxers…”
Adda closed his eyes and leaned back in his gauze net.
“Look,” said Maxx, “our bodies function by exploiting the Air’s mass transport properties… No? All right.” She pointed at the fan set into the wall. “Do you know why that fan is there — why there are fans installed throughout the City? To regulate the temperature — to keep us cool, here in the heat of the South Pole. The Air we inhabit is a neutron gas, and it’s made up of two components — a superfluid and a normal fluid. The superfluid can’t sustain temperature differences — if you heat it, the heat passes straight through.
“Now — that means that if you add more superfluid to a mass of Air, its temperature will drop. And similarly if you take superfluid out the temperature rises, because normal fluid is left behind. And that’s the principle the wall fans work on.”
Farr was frowning. “What’s that got to do with Adda?”
“Adda’s body is full of Air — like yours, and mine. And it’s permeated by a network of tiny capillaries, which can draw in superfluid to regulate his temperature.” Deni Maxx winked at Farr. “We have tiny Air-pumps in our bodies… lots of them, including the heart itself. And that’s what hair-tubes are for… to let Air out of your skull, to keep your brain the right temperature. Did you know that?”
“And it’s that mechanism which may not work so well, now, for Adda.”
“Yes. We’ve repaired the major vessels, of course, but they’re never the same once they’re ruptured — and he’s simply lost too much of his capillary network. He’s been left weakened, too. Do you understand that Air also powers our muscles?… Look — suppose you were to heat up an enclosed chamber, like this room. Do you know what would happen to the superfluid? Unable to absorb heat, it would flee from the room — vigorously, and however it could. And by doing so it would raise pressure elsewhere.
“When Adda wants to raise his arm, he heats up the Air in his lungs. He’s not aware of doing that, of course; his body does it for him, burning off some of the energy he’s stored up by eating. And when his lungs are heated the Air rushes out; capillaries lead the Air to his muscles, which expand and…”
“So you’re saying that because this capillary network is damaged, Adda won’t be as strong again?”
“Yes.” She looked from Dura to Farr. “Of course you do realize that our lungs aren’t really lungs, don’t you?”
Dura shook her head, baffled by this latest leap. “What?”
“Well, we are artifacts, of course. Made things. Or at least our ancestors were. Humans — real humans, I mean — came to this world, this Star, and designed us the way we are, so that we could survive, here in the Mantle.”
“The Ur-humans.”
Maxx smiled, pleased. “You know of the Ur-humans? Good… Well, we believe that original humans had lungs — reservoirs of some gas — in their bodies. Just as we do. But perhaps their lungs’ function was quite different. You see, our lungs are simply caches of Air, of working gas for the pneumatic systems which power our muscles.”
“What were they like, the Ur-humans?”
“We can’t be sure — the Core Wars and the Reformation haven’t left us any records — but we do have some strong hypotheses, based on scaling laws and analogies with ourselves. Analogous anatomy was my principal subject as a student… Of course, that was a long time ago. They were much like us. Or rather, we were made in their image. But they were many times our size — about a hundred thousand times as tall, in fact. Because he was dominated by balances between different sets of physical forces, the average Ur-human was a meter tall, or more. And his body can’t have been based, as ours is, on the tin-nucleus bond… Do you know what I’m talking about? The tin nuclei which make up our bodies contain fifty protons and one hundred and forty-four neutrons. That’s twelve by twelve, you see. The neutrons are gathered in a spherical shape in symmetries of order three and four. Lots of symmetry, you see; lots of easy ways for nuclei to fit together by sharing neutrons, plenty of ways for chains and complex structures of nuclei to form. The tin-nucleus bond is the basis of all life here, including our own. But not the Ur-humans; the physics which dominated their structure — the densities and pressures we think they inhabited — wouldn’t have allowed any nuclear bonding at all. But they must have had some equivalent of the tin bond…”
She held out her arms and wiggled her fingers. “So they were very strange. But they had arms, and legs, like us — so we believe, because otherwise why would they have given them to us?”
Dura shook her head. “That doesn’t make any sense.”
“Of course it does,” Maxx smiled. “Oh, fingers have their uses. But haven’t there been times when you’d have swapped your long, clumsy legs for an Air-pig’s jetfart bladder? Or for a simple sheet of skin like a Surfer’s board which would let you Wave across the Magfield ten, a hundred times as fast as you can now? You have to face it, my dear… We humans are a bad design for the environment of the Mantle. And the reason must be that we are scale models of the Ur-humans who built us. No doubt the Ur-human form was perfectly suited for whatever strange world they came from. But not here.”
Dura’s imagination, overheating, filled her mind with visions of huge, misty, godlike men, prising open the Crust and releasing handfuls of tiny artificial humans into the Mantle…
Deni Maxx looked deeply into Dura’s eyecups. “Is that clear to you? I think it’s important that you understand what’s happened to your friend.”
“Oh, it’s clear,” Adda called from his cocoon. “But it doesn’t make a blind bit of difference, because there’s nothing she can do about it.” He laughed. “Nothing, now she’s condemned me to this living hell. Is there, Dura?”
Dura’s anger welled like Deni’s heated superfluid. “I’m sick of your bitterness, old man.”
“You should have let me die,” he whispered. “I told you.”
“Why didn’t you tell us about Parz City? Why did you leave us so unprepared?”
He sighed, a bubble of thick phlegm forming at the corner of his mouth. “Because we were thrown out ten generations ago. Because our ancestors traveled so far before building a home that none of us thought we would ever encounter Parz again.” He laughed. “It was better to forget… What good would it do to know such a place existed? But how could we know they would spread so far, staining the Crust with their ceiling-farms and their Wheels? Damn them…”
“Why were we sent away from Parz? Was it because…” She turned, but Deni Maxx was making notes on a scroll with a Corestuff stylus, and did not appear to be listening. “Because of the Xeelee?”