The Nitrogen Fix

by Hal Clement

  “Breathe Freely!” he cried suddenly, and at the same moment he broke to his left up the hill.

  Moonlight showed fairly clear ground, and he made good speed. He had told the truth about being tired, of course, but he was in better physical condition by far than the city people. Two of the men sprang after him, but lost ground rapidly.

  The woman’s voice sounded after them. “Let him go, idiots! Come in here and recharge. We can get him easily enough! “ Flyn didn’t bother to look back to see whether the order was obeyed.

  It was as he had guessed, they would replace their breathing cartridges and go back to the raft area to wait for him. They might even go to the raft itself and wake up Kahvi, but they wouldn’t search it. She could say truthfully that he wasn’t there. Fyn himself could continue without interference eastward over the hilltop as long as he was in sight of the Hillers, and then on the other side turn south. He had air for most of the night, he knew. Even though he didn’t know the area well, Great Blue Hill could not be missed, and he knew there were several entrances. After finding one he could improvise.

  It actually took a good deal longer than he had expected to find an air lock, though he came at the hill from what he believed was the same direction he had always come before. The moon was high, the comet up, and he was starting to feel a little tense about breathing before he finally saw a pool which had to be an entrance to the city. There was no one around it, at least outside, as was to be expected at this hour.

  For a few minutes he hesitated. He suddenly realized how little he knew about what might lie ahead.

  Bones had not appeared — no surprise; Fyn had been sure the Hillers were wrong about his “follower.” It would be nice to have the native for company, though. Of course, there was nothing to be afraid of; the worst they would do would be to eject him, and even then they would give him enough air to reach the raft. His former captors would be there, but at least he would be no worse off.

  He glanced back at the bay, over two kilometers away, and wondered whether he could actually see the dark spot of the raft on the brightening water. He wondered why he sometimes did things without thinking them through, decided it was because there was so seldom sufficient time for that when emergencies arose.

  Then he entered the pool.

  VIII

  Doubt, Duplicated

  The other unit was lying on a pad of some material, presumably one of the pseudolife products so freely used by the human beings. It saw Bones at once, and in a single smooth movement came to its full height. This was little more than three quarters that of a typical human being; evidently this unit had been a bud not long before.

  It took two or three steps toward the newcomers and was stopped by the bars. Bones tried to wriggle free and cross the rest of the gap, but for some seconds had no luck. The bearers were unable to hold on, and allowed the suddenly not-so-limp form to drop to the stone floor, but they promptly piled on, seizing every available limb and preventing travel. Bones’ emotions did not match human ones very closely, but the howl of pain emitted by one of the people who grasped a glassstudded walking tentacle was rather satisfying even though the agony was mutual.

  Then a brief burst of human words sounded. “Let it go. See what they do. Keep the doorway blocked.” Bones couldn’t tell whether a male or a female was speaking, partly because of hearing system deficiencies and partly because the difference still meant nothing whatever to Observers, but three or four of the monosyllables carried meaning. It was no surprise when the human beings let go and stood back.

  The Observer could not stand; the pain in the rear walking tentacles was too great. The other limbs, however, were able to drag the streamlined form toward the bars and, when these were reached, to lift it nearly upright.

  The smaller figure’s upper tentacles lashed around Bones’ body; the larger one reciprocated. The rubbery forms could not actually squeeze between the bars, but were flexible enough for what was needed.

  On what corresponded to the human chest of each of the fishlike forms was a disc of specialized tissue a dozen centimeters across. Its color was little different from the olive green and brown mottling of the rest of the bodies; neither Earrin nor Kahvi had ever noticed it.

  Now the two discs pressed together as the tentacles tightened. Neither Observer felt the pain from the bars also being squeezed between them; neither felt anything but ecstasy. Neither had communicated for a long time. Memory cells flowed from one body to the other through the discs for more than a minute before the embrace relaxed, and for many more seconds the two held motionless while the transferred memories spread through their bodies, duplicated and reduplicated, and gradually as the glow faded rose to conscious level.

  When they finally separated, each was as nearly identical to the other in mind and memory as living creatures can ever be. Bones remembered everything that had led up to the smaller unit’s capture, and what had happened to it since then.

  The other remembered Bones’ experience with the Nomads for the last several years; it knew Earrin and Kahvi and their child; it would, on meeting any of them, be able to use the sign language which they and Bones had worked out to supplement oral speech, and it would understand human words as well as Bones, with the same auditory limitations, could.

  It knew Bones’ pain, and immediately on emerging from the pleasant daze which accompanied memory transfer the smaller being dropped to the floor and began removing with its fine-handling mouth tendrils the glass splinters which Bones had been unable to reach.

  The Observer wondered how the human beings would react to this, and rolled an eye or two in their direction. Surprisingly, only two people were now visible. Both were in the doorway, and both had their back turned to the Observers. The latter could not even guess at the reason for this behavior; the memory that Kahvi and Earrin preferred to be alone when they communicated bore no obvious relevance.

  For several more minutes the smaller being extracted glass, twice pausing for another brief embrace to firm the memory of where the splinters were located. Some of them had gone too deep to be seen or grasped, and had to be squeezed out with the aid of the more powerful handling tentacles.Eventually Bones was able to stand with reasonable comfort, though healing would take time. What should be done next was too obvious to be a matter for communication, though details were foggy. There was much to be learned about the underground city, since neither unit had seen much of it. This would require getting out of their present location and away from human control.

  The smaller unit, behind bars, would have the greater trouble with this. The concept of doors and locks for other than environmental purposes as in a spaceship, was foreign to the Observer mind, but they did remember how the prisoner had gotten into the cage originally. They were completely defeated by the padlock; the finer handling tendrils could get into the keyhole and determine the interior structure fairly well, but were not nearly strong enough to move any useful components. The smaller unit had of course found this out long before. There was a mystery here.

  Since the keyhole was obviously far too small for any human appendage, and no tool was present to do the job, the whole device must be intended to be opened only by some selected individuals. The concept of individual intelligence was growing, but the idea that some might act in direct conflict to the interest of others — even the idea that individuals could have conflicting interests — had not yet taken root in the Observer mind. Bones thought seriously of going to the door, getting the attention of a human being, and seeking help with the lock.

  The idea was dismissed after a moment; clearly the people did not want the Observers free to travel.

  However, there seemed nothing more to be learned here; there was nothing of interest in the room except pad, bars, and lock, and both units already knew all about these that their unaided senses could learn.

  Bones therefore walked to the door and pulled gently on the shoulder of one of the human beings.

  The latter turned at o
nce, and almost as quickly began to speak. The units could not get enough of the words to make connected sense of them.

  “They’ve finished!” was the cry that caused the other people to turn their attention back to the room.

  “The big one’s trying to get out!”

  “Don’t let it!” another voice called emphatically. “Three of you keep the door blocked. Get anyone outside to help. The rest, inside. Drive it into the cage — who has the key?”

  “I do.”

  “All right, you get the lock off and be ready to open the cage door when we get it near.” One of the human figures slipped past Bones. Three more — the group had increased in numbers — spread out to each side of the now blocked doorway and then converged toward the nearer captive. Bones could understand well enough that the idea was to get the second unit into the cage, and that this would require the opening of the door.

  Two sets of bulging eyes kept the human beings covered. The owners were not in real communication, but none was necessary; their minds had blended so recently that each knew what the other would think and how the other would act — though of course neither thought of the other as an other.

  Bones retreated to within two meters of the cage door, and saw it open under the handling of one of the people. As it did so, both Observers acted at once. The smaller one hurtled through the opening, colliding with the woman who had unlocked it and sending her to the floor. Bones’ handling tentacles simultaneously grasped two of those approaching and jerked them violently forward. One stumbled as intended and staggered through the door into the cage; the other kept his feet but came between Bones and the other humans. The two Observers raced around the off-balanced group and drove into the ones blocking the doorway. Their momentum was ample to break up the plug.

  There were no other people in the work room outside, and the escaping pair raced across it to the only door. Beyond this was the corridor through which they had been brought. Naturally, they separated; there was nothing to be gained by both seeing the same things. The smaller unit headed to the right, the direction which led back to the air lock.

  There were people in the tunnel that Bones followed, but not very many. Most of them went to some pains to avoid contact with the Observer.

  Presumably there would sooner or later be some organized effort to recapture the escaping pair, but there was no way of guessing how long this might take. For one thing, it would have to depend oncommunication, and this would have to be a slow process with the sound code — though the Observer still had doubts that this was really the only method available to the human species.

  Bones had no thought of hiding to avoid capture; this would have defeated the prime objective of learning as much as possible about the city and its inhabitants. This in fact called for communicating with the latter if at all possible, but apparently it wasn’t. None of the beings seemed even to realize that the waving appendages indicated a desire, much less an attempt, to talk to them. They either fled rapidly or backed cautiously away, usually producing loud sounds at the same time.

  That left little to learn except the pattern of the tunnels and the nature of any artifacts which might be found. The former had already given trouble, since they were not very straight; within minutes the Observer had to give up hope of finding, except by chance, either the lock through which the capture party had come or even the scene of the recent partial escape. Horizontal directions were bad enough, and it was obvious that the city extended vertically as well.

  At first it seemed wise not to leave the level of the lock until its details had been learned; there might be a need to leave the city. However, it was hard to see how such a need could arise, or could possibly carry as much weight as the need to learn, and presently Bones was as thoroughly lost in the third dimension as in the first two. It was not even possible to keep track of levels; the floors of Blue Hill were anything but horizontal. Boston, long before, had bragged that its street pattern represented the paving of the early settlers’ cow paths. The settlers’ descendants, who had excavated Blue Hill when it became evident that the change in Earth’s atmosphere could not be stopped, had similarly been guided by convenience in attacking the local geology. About the only rule had been to refrain from penetrating an existing room or tunnel without prior arrangement. There were corridors, living rooms, storage rooms, workshops, and large and small spaces whose purposes were beyond the Observer’s ability to guess in spite of years with the Fyn family.

  The incredible part was that all were deserted. There had been no human beings in sight since the first half hour or so after the escape. This would have been incomprehensible even if Bones had known about the more than seventy percent population drop since the city had been founded; surely the people would have been scouring the tunnels for the escaped aliens. By rights, they should have been back in custody within an hour of their escape; neither knew anything of the city, even the way out. Neither had anything which would serve as a weapon, and neither would have thought of using such a thing anyway. A population with any sort of organization and any agreement about what should be done would have had no trouble either in finding or securing their lost prisoners.

  The fact was, of course, that the group which had done the capturing was neither representative of the Hill population in general — as both Kahvi and Earrin were beginning to realize — nor particularly well organized. This was a consequence of the limited human communication faculties which Bones had so far come nowhere near to foreseeing. Both organization and its reverse where concepts which went with a population of individuals.

  Bones, therefore, had time to learn much detail about the city. Unfortunately, none of it led to meaningful generalizations, even when combined with the several years close observation of the Nomad family. It was trivial stuff.

  Eventually the researcher began to feel hungry. This was ordinarily a minor matter; practically any nitro-life that grew was acceptable food as long as reasonable balance was maintained between oxidizing and reducing vegetation. Inside Blue Hill’s caverns and corridors, however, there was no vegetation — the bioluminescent panels didn’t count. Thoughtful consideration of this problem suggested specific action.

  There was oxygen in the city, since the people went unmasked. Therefore, there were plants — photosynthetic organisms, synthetic or otherwise, similar to those maintained by Kahvi and Earrin on their raft and the various places on land where they sometimes stayed. These plants would presumably be edible, or have edible parts — many of the pseudolife-forms contained nitrates, though it was perhaps a bit doubtful that these would be found inside a human city.

  In any case, such plants would need sunlight; no other energy source could be available to human beings, judging by the Nomads’ attitude toward fire. Sunlight would be most available in the outer portions of the hill, and one way to get near the outside was to go up. As a matter of fact, both Kahviand Earrin had occasionally mentioned that the food and air sources of the cities were normally on the top levels.

  Bones, therefore, began taking every upward-slanting tunnel that presented itself. This quickly changed the surroundings, though not for the reason which might have been expected.

  Hemenway had not originally had an air plant section; the whole city was supplied from Great Blue Hill. The last few years, however, had brought changes.

  The tunnels were brighter; there were more of the luminescent panels on walls and ceiling, and they appeared to be watered and fed more carefully. If Bones had possessed a sense of smell it would have been obvious that the air was fresher; even without it, there was a certain subtle difference in the environment. The area was lived in.

  The impression was quickly supported more objectively. Within the same five minutes, Bones met two human beings. Both were adult, but considerably younger than Kahvi and her husband.

  Both reacted to sight of the Observer by a rapid retreat, accompanied by high-volume use of their voices. Both retreated in the same direction; Bones was, of cour
se, following the first when the second came on the scene. It seemed likely that they would lead the way to more interesting areas, so the Observer matched speeds with them instead of catching up as would have been so easy.

  The chase went on for several minutes without the cries of the human beings eliciting any response.

  Then an unusually steep upward ramp showed much brighter light at the top, light tinged with the golden color of sunlight filtered through an atmosphere containing distinct traces of nitrogen dioxide. Bones reached the foot of this slope just as the second of the people disappeared at the top, and started up without hesitation.

  There was clearly something to see up here.

  This proved correct, though the fleeing human beings had vanished. The sloping tunnel emerged at one side of a chamber some twenty meters square, roofed with the same transparent tissue used on the raft and the sail — Bones did not know the difference in the latter building. As with the jail, the tissue was supported at frequent intervals by thin beams — mere poles — of realwood. The sun was a brassy patch visible high in the south; only a few clouds showed in the golden sky.

  The room contained at least two dozen tables of the sort which carried plant trays in the jail, and most of these did carry flat, bubble-topped boxes in which growths of various shapes and colors could be seen. Few of these, however, bore close resemblance to the oxygen and nitrogen producers Bones knew from raft life. A few had the green of chlorophyll, but most were of strange reds, browns, and yellows. They might have been transplanted from among the nitro-life forms which covered most of the world outdoors, though it was hard to imagine Hillers doing such a thing, and the shapes of the organisms were mostly unfamiliar.