WILLIAM MORRISON
Country Doctor

He had long resigned himself to thinking that opportunity had passed him by for life. Now, when it struck so unexpectedly and so belatedly, he wasn't sure that it was welcome.
He had gone to sleep early, after an unusually hectic day. As if the need for immunizing against the threat of an epidemic hadn't been enough, he had also had to treat the usual aches and pains, and to deliver one baby, plus two premature Marsopolis calves. Even as he pulled the covers over himself, the phone was ringing, but he let Maida answer it. Nothing short of a genuine first-class emergency was going to drag him out of the house again before morning if he could help it. Evidently the call wasn't that important, for Maida hadn't come in to bother him about it, and his last feeling, before dropping off to sleep, was one of gratitude for her common sense.
He wasn't feeling grateful when the phone rang again. He awoke with a start. The dark of night still lay around the house, and from alongside him came the sound of his wife's slow breathing. In the next room, one of the kids, he couldn't tell which, said drowsily, "Turn off the alarm." Evidently the sound of the ringing hadn't produced complete wakefulness.
While he lay there, feeling too heavy to move, Maida moaned slightly in her sleep, and he said to himself, "If that's old Bender, calling about his constipation again, I'll feed him dynamite pills." Then he reached over to the night table and forced himself to pick up the phone. "Who is it?"
"Doctor Meltzer?" He recognized the hoarse and excited tones of Tom Linton, the city peace officer. "You better get over here right away!"
"What is it, Tom? And where am I supposed to get?"
"Over at the space port. Ship out of control—almost ran into Phobos coming down—and it landed with a crash. They need you fast."
"I'm coming."
The sleep was out of his eyes now. He grabbed his emergency equipment, taking along a plentiful supply of antibiotics and adjustable bandages. There was no way of knowing how many men had been hurt, and he had better be ready to treat an entire crew.
Outside the house, his bicar was waiting for him. He tossed in his equipment and hopped in after it. A throw of the switch brought in full broadcast power, and a fraction of a second later he had begun to skim over the smooth path that led over the farmland reclaimed from the desert.
The space port was less than twenty miles away, and it took him no more than ten minutes to get there. As he approached, the light blinked green at an intersection. Ah, he thought, one advantage of being a country doctor with a privileged road is that you always have the right of way. Are there any other advantages? None that you can think of offhand. You go through college with a brilliant record, you dream of helping humanity, of doing research in medicine, of making discoveries that will lengthen human life and lend it a little added happiness. And then, somehow, you find yourself trapped. The frontier outpost that's supposed to be the steppingstone to bigger things turns out to be a lifetime job. You find that your most important patients are not people, but food-animals. On Mars there are plenty of men and women, but few cows and sheep. Learn to treat them, and you really amount to something. Save a cow, and the news gets around faster than if you saved a man. And so, gradually, the animals begin to take more and more of your time, and you become known and liked in the community. You marry, you have children, you slip into a routine that dulls the meaning of the fast-hurrying days. You reach fifty—and you realize suddenly that life has passed you by. Half your alloted hundred years are gone, you can't tell where. The opportunities that once beckoned so brightly have faded in the distance.
What do you have to show for what the years have taken? One wife, one boy, one girl—
A surge of braking-power caught him from the direction of the space port. The sudden deceleration brought him out of his musings to realize that the entire area was brightly lit up. A huge ship lay across the middle of the field. Its length was at least a thousand feet, and he knew that there must be more than two dozen men in its crew. He hoped that none had been killed.
"Doc!"
Tom was rushing over to him. "How many hurt, Tom?"
"Our injuries are all minor, Doctor," said a sharp voice. "Nothing that I can't handle well enough myself."
As he stared at the man in the gold-trimmed uniform who was standing alongside Tom, he had a feeling of disappointment. If there were no serious injuries, what was the rush all about? Why hadn't they telephoned him while he was riding over, told him there was no need of him, let him get back to bed?
"I thought there was a serious crash."
"The crash was nothing, Doctor. Linton, here, was excited by our near-miss of Phobos. But we've no time to waste discussing that fact. I understand, Doctor Meltzer, that you're a first-class vet."
He flushed. "I hope you didn't drag me out of bed to treat a sick dog. I'm not sentimental about ship's pets—"
"This is no pet. Come along, and I'll show you."
He followed silently as the Captain led the way up the ramp and into the ship. Inside the vessel, there were no indications of any disorder caused by the crash. One or two of the men were bandaged around the head, but they seemed perfectly capable of getting around and doing their work.
He and the Captain were on a moving walkway now, and for three hundred feet they rode swiftly along it together, toward the back of the ship. Then the Captain stepped off, and Dr. Meltzer followed suit. When he caught sight of the thing that was waiting for him, he jaw dropped.
Almost the entire stern of the ship, about one third its length, was occupied by a great reddish creature that lay there quietly like an overgrown lump of flesh taken from some giant's butcher shop. A transparent panel walled it off from the rest of the ship. Through the panel Dr. Meltzer could see the thirty-foot-wide slit that marked the mouth. Above that was a cluster of breathing pores, looking like gopher holes, and above these was a semicircle of six great eyes, half closed and dulled as if with pain.
He had never seen anything like it before. "My God, what it it?"
"For lack of a better name, we call it a space-cow. Actually, it doesn't inhabit free space—we picked it up on Ganymede as a matter of fact—and as you can see, it doesn't resemble a cow in the least."
"Is that supposed to be my patient?"
"That's it, Doctor."
He laughed, with more anger than amusement. "I haven't the slightest idea what that behemoth is like and what's wrong with it. How do you expect me to treat it?"
"That's up to you. Now, wait a minute, Doctor, before you blow up. This thing is sick. It isn't eating. It hardly moves. And it's been getting worse almost from the time we left Ganymede. We meant to land at Marsopolis and have it treated there, but we overshot the place and when something went wrong with our drive we had no choice but to come down here."
"Don't they have any doctors to spare from town?"
"They're no better than you are. I mean that, Doctor. The vets they have in Marsopolis are used to treating pets for a standard series of diseases, and they don't handle animals as big as the ones you do. And they don't meet the kind of emergencies you do, either. You're as good a man as we can get."
"And I tell you, I don't know a thing about this overgrown hunk of protein."
"Then you'll just have to find out about it. We've radioed Earth, and hope to be getting some information soon from some of their zoo directors. Meanwhile—"
The crewmen were bringing over what appeared to be a diver's uniform. "What's this?" he asked suspiciously.
"Something for you to wear. You're going to go down into this animal."
"Into that mass of flesh?" For a moment horror left him with his mouth open. Then anger took over. "Like hell I am."
"Look, Doctor, it's necessary. We want to keep this beast alive—for scientific purposes, as well as possible value as a food animal. And how can we keep it alive unless we learn something about it?"
"There's plenty we can learn without going into it. Plenty of tests we can make first. Plenty of—"
He caught himself abruptly because he was talking nonsense and he knew it. You could take the thing's temperature—but what would the figure you got tell you? What was normal temperature for a space-cow? What was normal blood pressure—provided the creature had blood? What was normal heartbeat—assuming there was a heart? Presumably the thing had teeth, a bony skeleton—but how to learn where and what they were? You couldn't X-ray a mass of flesh like this—not with any equipment he had ever seen, even in the best-equipped office.
There were other, even more disquieting ways in which he was ignorant. What kind of digestive juices did the thing have? Suppose he did go down in a divers uniform —would the juices dissolve it? Would they dissolve the oxygen lines, the instruments he used to look around and probe the vast inside of the beast?
He expressed his doubts to the Captain, and the latter said, "These suits have been tested, and so have the lines. We know that they can stand a half hour inside without being dissolved away. If they start to go, you'll radio to us, and we'll pull you up."
"Thanks. How do I know that once the suit starts to go, it won't rip? How do I know that the juices simply won't eat my skin away?"
There was no answer to that. You just didn't know, and you had to accept your ignorance.
Even while he was objecting, Dr. Meltzer began putting on the suit. It was thin and light, strong enough to withstand several atmospheres of pressure, and at the same time not so clumsy as to hamper his movements considerably. Scaled pockets carried an assortment of instruments and supplies. Perfect two-way communication would make the exchange of ideas—such as they might be—as easy as if the person he was talking to were face to face with him. With the suit came a pair of fragile-looking gloves that left his hands almost as free as if they were bare. But the apparent fragility was misleading. Mechanical strength was there.
But what about resistance to biological action? The question kept nagging him. You can't know, he told himself. About things like that you take a chance. You take a chance and hope that if anything goes wrong, they'll pull you up before the juices have time to get working on you.
They had everything in readiness. Two of the other men were also wearing uniforms like his own, and when he had put his on, and tested it, the Captain gave the signal, and they all went into a small airlock. The door sealed behind them, a door in front opened. They were in the chamber where the great beast lay and quivered dully as if in giant pain.
They tied strong thin plastic cords around Doctor Meltzer's waist, tested the oxygen lines. Then they put a ladder up in front of the beast's face. Doctor Meltzer had a little trouble breathing, but it was not because of anything wrong with the oxygen supply. That was at the right pressure and humidity, and it was mixed with the correct amount of inert gases. It was merely the thought of going down into the creature's belly that constricted his throat, the idea of going into a strange and terrible world so different from his own, of submitting to unimaginable dangers.
He said hoarsely into the radio speaker, "How do I get in anyway, knock? The mouth's at least forty feet off the ground. And it's closed. You've got to open it, Captain. Or do you expect me to pry it open myself?"
The two men with him stretched out a plastic ladder. In the low gravity of Mars, climbing forty feet was no problem. Dr. Meltzer began to pull his way up. As he went higher, he noticed that the great mouth was slowly opening. One of the men had poked the creature with an electric prod.
Dr. Meltzer reached the level of the low jaw, and with the fascinated fear of a bird staring at a snake, gazed at the great opening that was going to devour him. Inside there was a gray and slippery surface which caught the beam of his flashlight and reflected it back and forth until the rays faded away. Fifty feet beyond the opening, the passage made a slow turn to one side. What lay ahead, he couldn't guess.
The sensible thing was to go in at once, but he couldn't help hesitating. Suppose the jaws closed just as he got between them? He'd be crushed like an eggshell. Suppose that throat constricted with the irritation he caused it? That would crush him too. He recalled suddenly an ancient fable about a man who had gone into a whale's belly. What was the man's name, now? Daniel—no, he had only gone into a den of lions. Job—wrong again. Job had been afflicted with boils, the victim of staphylococci at the other end of the scale of size. Jonah, that was it. Jonah, the man whose name was a symbol among the superstitious for bad luck.
But a scientist had no time for superstition. A scientist just thrust himself forward.
He stepped off the ladder into the great mouth. Beneath him, the jaw was slippery. His feet slid out from under him, and then his momentum carried him forward, and he glided smoothly down the yawning gullet. It was like going down a Martian hillside on a greased sled, the low gravity making the descent nice and easy. He noticed that the cords around his waist, as well as the oxygen lines, were descending smoothly after him. He reached the turn, threw his body away from the gray wall, and continued sliding. Another fifty feet, and he landed with a small plash in a pool of liquid.
The stomach? Never mind what you called it, this was probably the beginning of a digestive tract. He'd have a chance now to see how resistant his suit was.
He was immersed in the liquid now, and he sank slowly until his feet touched more solid flesh again. By the beam from his flashlight, he saw that the liquid around him was a light green. The portion of the digestive tract on which he stood was slate gray, with bright emerald streaks.
A voice spoke anxiously in his ears. "Doctor Meltzer! Are you safe?"
"Fine, Captain. Having a wonderful time. Wish you were here."
"What's it like in there?"
"I'm standing at the bottom of a pool of greenish liquid. I'm fascinated, but not greatly instructed."
"See anything that might be wrong?"
"How the devil would f tell right from wrong in here? I've never been in one of these beasts before. I've got sample bottles, and I'm going to fill them in various places. This is going to be sample one. You can analyze it later."
"Fine, Doctor. You just keep on going."
He flashed the beam around him. The liquid was churning gently, possibly because of the splash he himself had made. The gray-green walls themselves were quiet, and the portion underfoot yielded slightly as he put his weight upon it, but was otherwise apparently undisturbed by his presence.
He moved ahead. The liquid grew shallower, came to an end. He climbed out and stepped cautiously forward. "Doctor, what's happening?"
"Nothing's happening. I'm just looking around." "Keep us informed. I don't think there's any danger, but—"
"But in case there is, you want the next man to know what to watch out for? All right, Captain."
"Lines all right?"
"They're fine." He took another step forward. "The ground—I suppose I can call it the ground—is getting less slippery. Easier to walk on. Walls about twenty feet apart here. No sign of macroscopic flora or fauna. No artifacts to indicate intelligent life."
The Captain's voice sounded pained. "Don't let your sense of humor carry you away, Doctor. This is important. Maybe you don't realize exactly how important, but—"
He interrupted. "Hold it, Captain, here's something interesting. A big reddish bump, about three feet across, in the gray-green wall."
"What is it?"
"Might be a tumor. I'll slice some tissue from the wall itself. That's sample number two. Tissue from the tumor, sample number three."
The wall quivered almost imperceptibly as he sliced into it. The fresh-cut surface was purple, but it slowly turned red again as the internal atmosphere of the beast got at it.
"Here's another tumor, like the first, this time on the other side of the wall. And here are a couple more. I'm leaving them alone. The walls are getting narrower. There's still plenty of room to walk, but—wait a minute, I take that back. There's some kind of valve ahead of me. It's opening and closing spasmodically."
"Can you get through?"
"I'd hate to take a chance. And even if I did make it while it was open, it could crush the oxygen lines when it closed."
"Then that's the end of the road?"
"I don't know. Let me think."
He stared at the great valve. It moved rapidly, opening and closing in a two-second rhythm. Probably a valve separating one part of the digestive system from another, he thought, like the human pylorus. The green-streaked gray flesh seemed totally unlike human muscle, but all the same it appeared to serve a similar function. Maybe the right kind of drug would cause muscular relaxation.
He pulled a large hypodermic syringe from one of the sealed pockets of his diver's uniform. He plunged the needle quickly into the edge of the valve as it paused for a fraction of a second before closing, shot a pint of drug solution into the flesh, and ripped the needle out again. The valve closed once more, but more slowly. It opened, closed again, opened once more—and stayed open.
How long before it recovered, and shut off his retreat? He didn't know. But if he wanted to find out what was on the other side, he'd have to work fast. He plunged forward, almost slipping in his eagerness, and leaped through the motionless valve.
Then he called up to tell the Captain what he had done.
The Captain's voice was anxious. "I don't know whether you ought to risk it, Doctor."
"I'm down here to learn things. I haven't learned much yet. By the way, the walls are widening out again. And there's another pool of liquid ahead. Blue liquid, this time."
"Are you taking a sample?"
"I'm a sampler from way back, Captain."
He waded into the blue pond, filled his sample bottle, and put it into one of his pockets. Suddenly, in front of him something broke the surface of the pond, then dived down again.
He came to a full stop. "Hold it, Captain. There seems to be fauna."
"What? Something alive?"
"Very much alive."
"Be careful, Doctor. I think there's a gun in one of the pockets of that uniform. Use it if necessary."
"A gun? Don't be cruel, Captain. How'd you like to have somebody shooting off guns inside you?"
"Be careful, man!"
"I'll use my hypodermic as a weapon."
But the creature, whatever it was, did not approach him again, and he waded further into the blue pool. When his eyes were below the surface of the liquid, he saw the thing moving again.
"Looks like an overgrown tadpole, about two feet long." "Is it coming close?"
"No, it's darting away from me. And there's another one. I think the light bothers it."
"Any signs that the thing is dangerous?"
"I can't tell. It may be a parasite of the big creature, or it may be something that lives in symbiosis with it."
"Stay away from it, Doctor. No use risking your life for nothing."
A trembling voice said, "Larry! Are you all right?" 
"Maida! What are you doing here?"
"I woke up when you left. And then I had trouble going to sleep again."
"But why did you come to the space port?"
"Ships began to flash by overhead, and I began to wonder what had happened. So I called up—and they told me."
"Ships overhead?"
The Captain's voice cut in again. "The news services, Doctor. This case has aroused great interest. I didn't want to tell you before, but don't be surprised if you come up to find yourself famous."
"Never mind the news services. Have you heard from Earth yet?"
"No messages from Earth. We did hear from the curator of the Marsopolis Zoo."
"What did he say?"
"He never even heard of a space-cow, and he has no suggestions to make."
"That's fine. By the way, Captain, are there any photographers around from those news services?"
"Half a dozen. Still, motion picture, television—"
"How about sending them down inside to take a few pictures?"
There was a moment of silence. Then the Captain's voice again: "I don't think they can go down for a while yet. Maybe later."
"Why can't they go down now? I'd like to have some company. If the beast's mouth is open—" A disquieting thought struck him. "Say, it is open, isn't it?"
The Captain's voice sounded tense. "Now, don't get upset, Doctor, we're doing all we can!"
"You mean it's closed?"
"Yes, it's closed. I didn't want to tell you this, but the mouth closed unexpectedly, and then, when we did have the idea of sending a photographer down inside, we couldn't get it open again. Apparently the creature has adapted to the effects of the electric shock."
"There must be some way of getting it open again."
"Of course there's a way, There's always a way. Don't worry, Doctor, we're working on it. We'll find it."
"But the oxygen—"
"The lines are strong, and the mouth isn't closed tight enough to pinch them off. You can breathe all right, can't you?"
"Now that I think of it, I can. Thanks for telling me." 
"You see, Doctor, it isn't so bad."
"It's perfectly lovely. But what happens if my uniform or the oxygen lines start to dissolve?"
"We'll pull you out. We'll do something to open the mouth. Just don't get caught behind that valve, Doctor."
"Thanks for the advice. I don't know what I'd do without it, Captain."
He felt a sudden surge of anger. If there was one thing he hated, it was good advice, given smugly when the giver could stand off to one side, without sharing the danger of the person he was helping. Don't let this happen, don't get caught here, take care of yourself. But you were down here to do a job, and so far you hadn't done it. You hadn't learned a thing about what made this monstrous creature tick.
And the chances were that you wouldn't learn, either. The way to examine a beast was from the outside, not from within. You watched it eat, you studied the transfer of the food from one part of the body to another, you checked on the circulation of the body fluids, using radioactive tracers if no other methods offered, you dissected specimens of typical individuals. The Captain should have had a few scientists aboard, and they should have done a few of these things instead of just sitting there staring at the beast. But that would have made things too easy. No, they had to wait for you to come aboard, and then send you deliberately sliding down into the guts of an animal you didn't know anything about, in the hope of having a miracle happen to you. Maybe they thought a loop of intestine or some gland of internal secretion would come over to you and say, "I'm not working right. Fix me, and everything will be fine."
Another of the tadpole-like creatures was swimming over toward him, approaching slowly, the forepart twitching like the nose of a curious dog. Then, like the others, the creature turned and darted away. "Maybe that's the cause," he thought. "Maybe that's the parasite that's causing the trouble."
Only—it might just as well be a creature necessary to the larger creature's health. Again and again you were faced with the same problem. Down here you were in a world you knew nothing about. And when everything was so strange to you—what was normal, and what wasn't?
When in doubt, he decided, move on. He moved.
The blue pool was shallow, and once more he came up on what he decided to call dry ground. Once more the walls grew narrow again. After a time he could reach out and touch the walls on either side of him at the same time.
He flashed his light into the narrow passage, and saw that a dozen yards ahead of him it seemed to come to an end. "Blind alley," he thought. "Time to turn back."
The Captain's voice came to him again, "Doctor, is everything all right?"
"Beautiful. I've had a most interesting tour. By the way, did you get the creature's mouth open yet?"
"We're still working on it."
"I wish you luck. Maybe when those reports from Earth come in—"
"They've come. None of the curators knows anything about space-cows. For some reason, the electric shock method doesn't work any more, and we're trying all sorts of other stimuli."
"I take it that nothing is effective."
"Not yet. One of the photo service men suggested we use a powerful mechanical clamp to pull the jaws open. We're having one flown over."
"Use anything," he said fervently. "But for God's sake, get that mouth open!"
Dr. Meltzer cursed the photo service people, to whom he meant nothing more than a series of colored lines in space. Then he added an unkind word or two for the Captain, who had got him into this mess, and started back.
The tadpole creatures seemed to be interested in his progress. They came swarming around him, and now he could see that there were almost a dozen of them. They moved with quick flips of their tails, like the minnows he had once seen back on Earth, where he had attended medical school. Between each pair of flips there was a momentary pause, and when they came close he was able to get a reasonably good look at them. He was surprised to see that they had two rows of eyes each.
Were the eyes functional or vestigial? In the former case, they must spend some part of their life cycle outside the host creature, in places where they had need of the sense of sight. In the latter case, they were at least descended from outside creatures. Maybe I'll try to catch one of them, he thought. Once I get it outside I can give it a real examination.
Once I get it outside, he repeated. Provided I get outside myself.
He waded through the pond again. As he reached the shallow part of the blue liquid, a voice came to him—this time his wife's voice. "Larry, are you all right?"
"Doing fine. How are the kids?"
"They're with me. They woke up during the excitement, and I brought them along."
"You didn't tell me that before!"
"I didn't want to upset you."
"Oh, it doesn't upset me in the least. Nothing like a nice family picnic. But how do you expect them to go to school in the morning?"
"Oh, Larry, what difference does it make if they miss school for once? A chance to be in on something like this happens once in a lifetime."
"That's a little too often to suit me. Well, now that I know they're here, let me talk to them."
Evidently they had been waiting for the chance, for Jerry's voice came at once. "Hiya, Dad."
"Hiya, Jerry. Having a good time?"
"Swell. You oughtta be out here, Dad. There are a lot of people. They're treatin' us swell."
Martia cut in. "Mom, he isn't letting me talk. I want to talk to Daddy too."
"Let her talk, Jerry. Go ahead, Martia. Say something to Daddy."
A sudden blast almost knocked out his eardrum. "Dad, can you hear me?" Martia screamed. "Can you hear me, Dad?"
"I can hear you, and so can these animals. Not so loud, sweetheart."
"Gee, Dad, you oughtta see all the people. They took pictures of me and Mom. Oh, we're so thrilled!"
"They took pictures of me too, Dad," said Jerry.
"They're sending the pictures all over. To Earth and Venus, and everywhere. We're gonna be on television too, Dad. Isn't it exciting?"
"It's terrific, Martia. You don't know what this does for my morale."
"Aw, all she thinks about is pictures. Mom, make her get away from the microphone, or I'll push her away."
"You've had your chance, Martia. Let Jerry talk again."
"You know what, Dad? Everybody says you're gonna be famous. They say this is the only animal of its kind ever discovered. And you're the only person ever went into it. Can I go down there too, Dad?"
"No!" he yelled.
"Okay, okay. Say, Dad know what? If you bring it back alive, they're gonna take it to Earth, and put it in a special zoo of its own."
"Thank them for me. Look, Jerry, did they get the animal's mouth open yet?"
"Not yet, Dad, but they're bringing in a great big machine."
The Captain's voice again: "We'll have the mouth open soon, Doctor. Where are you now?"
"Approaching the valve again. Having you heard anything that could be useful? Maybe some explorer or hunter might be able to tell you something about space-cows—"
"Sorry, Doctor. Nobody knows anything about space-cows."
"That's what you said before. All right, Captain, stand by for further news. I've got a shoal of these tadpole beasts in attendance. Let's see what happens now."
"They're not attacking, are they?"
"Not yet."
"You feel all right otherwise?"
"Fine. A little short of breath, though. That may be the result of tension. And a little hungry. I wonder how this beast would taste raw—my God!"
The Captain asked anxiously, "What is it?"
"That valve I paralyzed. It's working normally once more!"
"You mean it's opening and closing?"
"The same rhythm as before. And every time it closes, it squeezes those oxygen tubes. That's why I sometimes feel short of breath. I have to get out of here!"
"Do you have enough drug to paralyze the valve again?"
"No, I don't. Keep quiet, Captain, let me figure this out."
"That valve I paralyzed. It's working normally once more!" place to take off from.
He might have dived safely through the opening during the near-second when the muscles were far apart. But there was no place for a take-off. He had to approach up a slippery slope, hampered by uniform and lines. And if he misjudged the right moment to go through, he'd be caught when the valve closed again.
He stood there motionless for a moment, sweat pouring down his forehead and into his eyes. Damn it, he thought, I can't even wipe it away. I've got to tackle this thing half blind.
Through one partially fogged eyeplate he noticed the tadpole creatures approaching more closely. Were they vicious after all? Were they coming closer because they sensed that he was in danger? Were they closing in for the kill?
One of them plunged straight at him, and involuntarily he ducked. The thing turned barely aside at the last moment, raced past him, slithered out of the blue liquid, and squirmed up the slope toward the valve.
Unexpectedly, the valve opened to twice its previous width, and the creature plunged through without trouble. "Doctor Meltzer? Are you still all right?"
"I'm alive, if that interests you. Listen, Captain, I'm going to try getting through that valve. One of the tadpole beasts just did it, and the valve opened a lot wider to let it through."
"Just how do you expect to manage?"
"I'll try grabbing one of the beasts and hitch-hike through. I just hope it isn't vicious, and doesn't turn on me."
But the tadpole creatures wouldn't let themselves be grabbed. In this, their home territory, they moved a great deal faster than he did, and even though they didn't seem to be using their eyes to see with, they evaded his grasp with great skill.
At last he gave up the attempt and climbed out of the blue pool. The creatures followed him.
One of the biggest of them suddenly dashed forward. Sensing what the thing was going to do, Dr. Meltzer hurried after it. It scurried up the slope, and plunged through the valve. The valve opened wide. Dr. Meltzer, racing desperately forward, threw himself into the opening. The valve paused, then snapped at him. He felt it hit his heel.
The next moment he was gasping for breath. The oxygen lines had become tangled.
He fought frenziedly to untwist them, and failed. Then he realized that he was trying to do too much. All he needed to do was loosen the knot and straighten out the kinks. By the time he finally succeeded, he was seeing black spots in front of his eyes.
"Doctor Meltzer, Doctor Meltzer!"
The sound had been in his ears for some time. "Still alive," he gasped.
"Thank God! We're going to try to open the mouth now, Doctor. If you hurry forward, you'll be in a position to be pulled out."
"I'm hurrying. By the way, those tadpoles are still with me. They trailing along as if they'd found a long-lost friend. I feel like a pie-eyed piper."
"I just hope they don't attack."
"You're not hoping any harder than I am."
He could catch his breath now, and with the oxygen lines free, the perspiration that had dimmed his sight slowly evaporated. He caught sight of one of the reddish tumors he had noticed on his forward passage.
"May as well be hung for a sheep as a lamp," he murmured. "It would take an axe really to chop that tumor out, but I may as well slice into it and see what I can learn."
From one of his pockets he took a sharp oversize scalpel, and began to cut around the edges.
The tumor throbbed convulsively.
"Well, well, I may have something here," he said, with a surgeon's pleasure. He dug deeper.
The tumor erupted. Great gobs of reddish liquid spurted out, and with one of them came another of the tadpole creatures, a small one, half the average size of those he had first encountered.
"Glory be," he muttered. "So that's the way they grow."
The creature sensed him and darted aside, in the direction of the valve. As it approached, the open valve froze in place, and let the small creature through, further into the host, without enlarging. Then the valve began to close again.
They're adapted to each other, he thought. Probably symbiosis, rather then a one-sided parasitism.
He moved upwards, toward the greenish liquid. An earthquake struck.
The flesh heaved up beneath his feet, tossing him head over heels into the pool. The first shock was followed by a second and third. A tidal wave hit him, and carried him to the side of the pool. He landed with a thud against the hard side and bounced back.
The sides began to constrict, hemming him in.
"Captain!" he yelled. "What's going on out there? What are you doing to the beast?"
"Trying to pry open its mouth. It doesn't seem to like the idea. It's threshing around against the walls of the ship."
"For God's sake, cut it out! It's giving me a beating in here."
They must have halted their efforts at once, for immediately afterwards the beast's movements became less convulsive. But it was some time before the spasmodic quivering of the side walls came to an end.
Dr. Meltzer climbed out of the pool of liquid, making an automatic and entirely useless gesture to wipe the new perspiration from his forehead.
"Is it better in there, Doctor?"
"It's better. Don't try that again," he panted. 
"We have to get the mouth open some way." 
"Try a bigger electric shock."
"If you want us to. But it may mean another beating for you, Doctor."
"Then wait a minute. Wait till I get near the upper part of the gullet."
"Whenever you say. Just tell us when you're ready."
Better be ready soon, he thought. My light's beginning to dim. When it goes out altogether, I'll probably be in a real panic. I'll be yelling for him to do anything, just to get me out of there.
And what about the suit and the oxygen lines? I think the digestive fluid's beginning to affect them. It's hard to be sure, now that the light's weakening, but they don't have the clear transparent look they had at first. And when they finally go, I go with them.
He tried to move forward faster, but the surface underfoot was slimy, and when he moved too hastily, he slipped. The lines were getting tangled too. Now that the creature's mouth was closed, it was no use tugging at the cord around his waist. That wouldn't get him up.
"Doctor Meltzer!"
He didn't answer. Instead, he pulled out his lancet and cut the useless cords away. The oxygen lines too were a nuisance, in constant danger of kinking and tangling, now that they were no longer taut. But at least the gas was still flowing through them and would continue to flow—until the digestive fluid ate through.
The tadpole creatures seemed to have developed a positive affection for him. They were all around him, not close enough for him to grab them, but too close for comfort. At any moment they might decide to take a nip out of his suit or an oxygen line. And with the plastic already weakened, even a slight tear might be fatal.
He reached the sharp slope that signified the gullet. "Dr. Meltzer?"
"What do you want?"
"Why didn't you answer?"
"I was busy. I cut the cords away from around my waist. Now I'm going to try climbing up inside this thing's throat."
"Shall we try that sharp electric shock?"
"Go ahead."
He had a pair of small surgical clamps, and he took one in each hand. The flashlight he put in a holder at his waist. Then, getting down on all fours, he began to crawl up, digging each pair of clamps into the flesh in turn to give him a grip. A slow wave ran away in both directions every time he inserted one of the pairs of clamps into the flesh, but otherwise the beast didn't seem to mind too much.
He was about halfway up, when the earthquakes began again. The first one sent him tumbling head over heels down the slope. The others added some slight injury to the insult, knocking him painfully against the walls. They must have used a powerful electric jolt, for some of it was transmitted through the creature to him, making his skin tingle. He hadn't lost his flashlight, but by now it was exceedingly dim, and shed only a feeble circle of light. Far ahead of him, where the mouth was to open, was blackness.
"No luck, Captain?"
"No luck, Doctor. We'll try again."
"Don't. You just make things worse."
"Larry, were you hurt? Larry—"
"Don't bother me now, Maida," he said roughly. "I have to figure out a way to get out."
A faint hiss came from the oxygen line. A leak. Time was growing short.
The tadpole creatures were swimming around faster now. They too must have been upset by the shock. One of them darted ahead of him, and wriggled ahead until it was lost in blackness.
That seems to be trying to get out too, he told himself. Maybe we can work this together. There must be some way, something to get this creature to open its mouth. Maybe the Captain can't do it from outside, but I'm in here, where the beast's most sensitive. I can hit it, slash at it, tickle it—
There's a thought. Tickle it. It's a monster, and it'll take some monstrous tickling, but sooner or later, something should affect it.
He stamped hard with his foot. No effect. He took his large lancet from his pocket and slashed viciously with it. A shudder ran through the flesh, but that was all.
And then he had an idea. That green liquid undoubtedly contained hormones. Hormones, enzymes, co-enzymes, antibiotics, biological chemicals of all kinds. Stuff to which some tissues would be adapted and some would not. And those that weren't would react violently.
He turned back, filled his hypodermic syringe with the greenish liquid, and ran forward again. The light was almost gone by now, and the hissing from the oxygen line was growing ominously, but he climbed forward as far as he could before plunging the hypodermic in and injecting its contents.
The creature heaved. He dropped hypodermic, light, and clamps, and let the huge shuddering take him where it would. First it lifted him high. Then it let him fall suddenly—not backwards, but in the same place. Two of the tadpole beasts were thrown against him. Then he was lifted way up again, and this time forward. A huge cavern opened before him. Light bathed the gray surface and he was vomited out.
The light begun to flicker, and he had time for one last thought. Oxygen lack, he told himself. My suit's ripped, the lines have finally torn.
And then blackness.
When he came to, Maida was at his side. He could see that she had been crying. The Captain stood a little further off, his face drawn, but relieved.
"Larry, dear, are you all right? We thought you'd never get out."
"I'm fine." He sat up and saw his two children, standing anxious and awestricken on the other side of the bed. Their silence showed how strongly they had been affected. "I hope you kids didn't worry too much about me."
"Of course I didn't worry," said Jerry bravely. "I knew you were smart, Dad. I knew you'd think of a way to get out."
"While we're on the subject," interposed the Captain, "What was the way out?"
"I'll tell you later. How's the patient?"
"Doing fine. Seems to have recovered completely."
"How many of the tadpoles came out with me?"
"About six. We're keeping them in the same low-oxygen atmosphere as the creature itself. We're going to study them. We figure that if they're parasites—"
"They're not parasites. I finally came to a conclusion about them. They're the young."
"What?"
"The young. If you take good care of them, they'll eventually grow to be as big as the mother-monster you've got in the ship."
"Good God, where will we keep them?"
"That's your worry. Maybe you'd better expand that zoo you're preparing. What you'll do for money to feed them, though, I don't know."
"But what—"
"The trouble with that monster—its `illness'—was merely that it was gravid."
"Gravid?"
"That means pregnant," exclaimed Jerry.
"I know what it means." The Captain flushed. "Look, do we have to have these kids in here while we discuss this?"
"Why not? They're a doctor's children. They know what it's all about. They've seen calves and other animals being born."
"Lots of times," said Martia.
"Confined as it was on the ship, your beast couldn't get the exercise it needed. And the young couldn't get themselves born."
"But that was the digestive tract you went down—"
"What of it? Are all animals born the same way? Ask the average kid where a baby grows, and he'll tell you that it's in the stomach."
"Some kids are dopes," said Jerry.
"They wouldn't be in this case. What better place to get a chance at the food the mother eats, in all stages from raw to completely digested? All that beast needed to give birth was a little exercise. You gave it some from the outside, but not enough. I finished the job by injecting some of its own digestive fluid into the flesh. That caused a pretty little reaction."
The Captain scratched his head. "Doctor, you did a good job. How would you like to take care of that beast permanently? I could recommend you—"
"To go down inside that monster again? No, thanks. From now on, I treat nothing but small monsters. Sheep, cows—and human beings."
There was a pounding of feet in the hallway. Then the door swung in, violently. Flashbulbs that gave invisible light began to pop with inaudible bursts of high-frequency sound. Cameras pointed menacingly at him and sent his image winging to Earth and far-off planets. Reporters began to fire their questions.
"My God," he muttered wearily, "who let these animals in here? They're worse than the ones I met inside the blue pool."
"Be nice to them, dear," chided Maida gently. "They're turning you into a great man."
Then Maida and Jerry and Martia grouped themselves around him, and the cameras caught them too. The proud look on their faces was something to see. And he realized that he was glad for their sake.
Opportunity had knocked, and when he had opened the door to it, it had proved to be an exacting guest. Still, he hadn't been a bad host—not a bad host at all, he thought. And slowly his features relaxed into a tired and immediately famous grin.