The City of the Sun (4 page)

That, of course, was one of the most worrying things. If the people of the city were all infected by this thing then they obviously hadn’t put up much of a fight. One of the first things the colonists would have done would have been to prepare some biotic defenses against their new environment. Simple medical technology is the first priority of any colony.

The cards told me that the dendrites ramified internally as well as externally, but only to a limited extent. The bulk of the biomass lay on the surface, with only thin threads—chains of potentially independent cells—linking it to the circulatory system and the nervous system of the host. The parasite was careful not to damage its hosts by too much disruption of the tissues. It didn’t feed on tissues—just leeched what it required from the bloodstream. A very considerate vampire, if appearances were to be believed. The surveyors reported that infected animals were at least as healthy as uninfected ones.

Then I saw something on one of the cards that made me put the others aside.

“If anyone wants to bet,” I said, “I’ll lay six to four on
this
one as the culprit.”

There were no takers, but they all wanted to know why.

“It’s the special one,” I told them. “It has a footnote that the survey team didn’t think was especially significant. It says here that this particular species goes in for inductive cellular mimicry. Especially with respect to nervous tissue.”

“Which means?” Nathan prompted.

“These communal protozoans are versatile,” I said. “It’s the key to their success. Some protozoan species on Earth are versatile enough to choose whether to be plants or animals—they can grow chloroplasts and dispose of them as circumstances dictate. The whole essence of communal aggregation is that it’s the beginnings of division of labor—some cells specialize in reproduction, others in energy fixation, others in defense. It happens in the colonial algae and in the colonial polyps. The point about communal aggregations, though, is that the cells retain their potential independence—and their potential choices. Organisms—multicellular organisms, that is—go in for a much more precise kind of specialization. Once a cell grows to its destined function it remains specialized. Once a liver cell, always a liver cell—the versatility of each individual cell is lost at an early stage in the development of an embryo when cells become fixed into their permanent function. This process of specialization is involved with a mechanism called induction, which causes different tissues to develop in the right places within the embryo in response to the stimuli provided by other tissues developing in the immediate environment.

“These parasites, being communal pseudo-organisms, retain essential versatility in each and every cell. Most of the species don’t make a lot of use of that versatility—parasitism is a relatively simple way of life, which doesn’t demand a great deal of differentiation of functions. But
this
one is a very highly developed parasite...a super-parasite. You can think of the others as plant-like things, sending tap roots down into the flesh of their hosts to soak up moisture and nourishment. It’s essentially a crude business, like drilling oil wells. The parasites are fairly discreet—they use thin drills, strands of cells only two or three thick—but what they do is nevertheless a fairly straightforward job of boring and mining.

“The odd man out is cleverer than that.
His
cells make use of their versatility by mimicking the cells of the host. Thus, when he sends a tap root down through skin tissue to the wall of a blood vessel, the strand cells take on many of the characteristics of dermal cells, and the cells which actually do the thieving take on many of the characteristics of blood-vessel-wall cells. This parasite then has a much higher degree of integration with his host. The host no longer recognizes him as an invader, and thus he becomes immune to the body’s natural tendency to reject foreign matter. The
extra
functions fulfilled by these cells—the parasite functions—are masked by the apparent conformity of the cells to their immediate tissue environment.

“I can’t tell from this report how far the mimicry goes. But if this parasite is
really
clever—and we have grounds to suspect that it is—then the mimic cells might
actually
carry out the functions of the tissues they mimic, so that as well as the tap root cells being indistinguishable from host-tissue cells by the host’s bodily defenses, they actually do the job they ought to be doing if they
were
host-tissue cells. That way, this particular parasite could maintain a much more extensive internal network than its relatives. It wouldn’t have to limit itself to a few discreet strands of cells—it could ramify much more extensively inside its host. And that would mean that it could support a much greater biomass all told—something like the formations we could see on these people, instead of just a little thing like a spider web on the back of a rabbit.

“Also, of course, this could explain why the colonists might have been unable to muster any kind of medical defense against this parasite. If its internal ramifications can mimic host cells well enough to fool the host body itself, no external antibiotic would get close to it...not without attacking the host tissues too. The external dendrites—the black cells—are probably fairly easy to dispose of...but if the colonists dispose of them they simply grow back from inside. The roots can’t be touched by any normal methods.

“In brief, I suspect that this is the most efficient parasite I’ve ever come across. Maybe it’s so efficient that it doesn’t deserve to be called a parasite—maybe just a commensal. It really cooperates with the host body, taking the nourishment it needs with the absolute minimum of biotic vandalism. Maybe the only thing we can say against it is that it isn’t very pretty. Maybe...I think I’ll reserve judgment on that until I get a much closer, much longer look.”

There was a respectful pause.

“You may applaud,” I told them.

They didn’t. Not that it mattered. I hadn’t planned an encore.

“If you’re right,” said Nathan, “then the obvious question is...can we find any way to attack such a parasite?”

“Oh yes,” I assured him. “Genetic engineering gives us much more subtle routes of attack than any antibiotic drug. We can actually attack the thing in its genes—the very genes which give it its versatility and its ability to mimic specialized cells. The parasite cells can only mask their real nature...and we have the means to get behind the mask. It probably won’t pose much of a problem to us, if only....”

“...if only we can persuade them that it’s a problem,” Nathan finished for me. I hated him pinching my punch line like that.

I shrugged. “People do get used to things,” I said. “They may not see this stuff quite as we see it. They may like black stripes growing all over them.”

“Well,” said Linda, with commendable pragmatism, “if the parasite really doesn’t do them any harm, they can afford to like it, can’t they? And we can afford to let them.”

“I think,” I said, “that I’d like to reserve judgment on that issue too. Until I’ve had a much longer and much closer look. I’ve got this strong suspicion, still, that there’s a lot more to this than we’ve so far guessed.”

“Isn’t there always?” put in Karen.

He ducked the issue. “They probably brought two mounts because they’re expecting two of us,” he said. “You can ride with Mariel...you’re the only one of us who’s had practice riding all manner of weird creatures. You help her and I’ll manage on my own.”

He turned away as soon as he finished, not leaving me space to argue. I cursed silently and followed him, thinking:
At least I get to see how you explain why we’re now all dressed up in plastic bags.

But I was wrong. He didn’t explain. He just stepped out of the lock and went to meet our silver-clad friend as if nothing could be more natural than wearing a plastic bag. I watched the dark man/woman’s eyes narrow slightly in surprise, but he/she made no reference to the matter. Politeness is a wonderful thing.

“You may come to the city,” he/she said. “The Ego will interrogate you. Then the Self will decide whether you are to stay.”

Then he/she saw Mariel coming out of the lock behind us.

His/her only comment was: “Two of you must ride together.”

The archers were waiting with the spare mounts at the same respectful distance they had maintained during our morning meeting. But now we could approach them. I set off with an eager stride, glancing up at the dark man/woman as I passed his/her placid beast. He/she looked back, his/her face quite impassive and his/her body apparently quite relaxed.

Nathan lagged a few paces behind and fell into step with Mariel.

I heard her say: “Nothing...I can’t read anything.”

“Stay with it,” he said. “Relax and take your time.”

Their voices sounded a little hoarse filtered through the vocal apparatus of the suits, which made whispering a little difficult.

My attention was fixed ahead, though. As I came closer to the naked archers I took a good long look at the way the parasite extended itself over the body. I also checked what I hadn’t been quite sure of earlier in the day—the absence of pubic hair. The hair was missing, of course...but it wasn’t all that was missing.

The archers were all of full adult size—five and a half to six feet tall. They had neither beards nor wrinkles, and it wasn’t easy to make a guess at their ages, but none of them were children. But the ones I could see, though definitely male, had sexual organs that were either undeveloped or vestigial. In brief, no balls.

I looked back over my shoulder at the man in the silver tunic. Man he was, I decided. The silvery voice which went with the clothes had simply never broken.

It was something I might have anticipated, at least as one of a number of possibilities, but somehow the thought just hadn’t crossed my mind. It came as a shock, now.

I arrived at the waiting mounts, and the archer passed the reins to me. I said “thanks” but he didn’t seem to be paying any attention. Now I was close, it struck me what a long way it was from the ground to the ridge of the shaggy back. There was no stirrup to help me up. I’d ridden a lot of animals in my time, including some extremely tall camels, but nothing as weird as this creature. And camels will bend down for you if you ask them nicely.

I passed one of the reins to Nathan and stood back, quite happy to let him take first crack at getting aboard. He’d done most things in his long and colorful life—maybe including riding camels—but when you do just about everything you don’t get much practice at anything in particular. I was wondering how he’d go about it.

I should have guessed.

“Give me a leg up, will you?” he said.

I sighed, and let him put his knee into the palm of my hand, then boosted him up. I did the same for Mariel. She took a handful of mane and offered her other hand to me. Somehow, with that assistance, I contrived to end up on the beast’s back sitting just behind her. We’d never have managed it but for the perfect docility of the mounts themselves.

I watched Mariel part the mane with her gloved fingers to expose the tracing of black lines against the skin. They were very thin lines, with no gathering at any point into a considerable mass. But on the backs of the archers, I saw, from the base of the neck extending like the silhouette of a bird with wings spread wide, was a large expanse of parasite tissue...a kind of shallow hump.