The first heartbeat broke the spell in the control-tower. Carter raised both hands in the air and shook them in mute invocation of the gods. "Made it, by thunder. Brought them through!"

Reid nodded. "You won that time, general. I wouldn't have had the nerve to order them through the heart."

The whites of Carter's eyes were bloodshot. "I didn't have the nerve not to order it. Now if they can hold up against the arterial flow . . ." His voice rang out into the transmitter. "Get into touch with the Proteus the moment their speed diminishes."

Reid said, "They're back in the arterial system, but they're not heading for the brain, you know. The original injection was into the systemic circulation, into one of the main arteries leading from the left ventricle to the brain. The pulmonary artery leads from the right ventricle-to the lungs."

"It means delay. I know that," said Carter. "But we still have time." He indicated the Time Recorder, which read 48.

"All right, but we'd better switch the point of maximum concentration to the respiration center."

He made the appropriate change and the interior of the respiration post was visible on the monitor screen. Reid said, "What's the respiration rate?"

"Back to six per minute, colonel. I didn't think we were going to make it there for a second."

"Neither did we. Hold it steady. You're going to have to worry about the ship. It will be in your sector in no time."

"Message from the Proteus," came another voice. "ALL WELL. Uh, sir? There's more, do you want it read?"

Carter scowled. "Of course, I want it read."

"Yes, sir. It says: WISH YOU WERE HERE AND I WERE THERE."

Carter said, "Well, you tell Grant that I would rather a hundred times he ... No, don't tell him anything. Forget it."

The end of the heartbeat had brought the surge forward to a manageable velocity, and the Proteus was moving along smoothly again, smoothly enough to make it possible to feel the soft, erratic Brownian motion.

Grant welcomed that sensation, for it could be felt only in the quiet moments and it was those quiet moments that he craved.

They were all out of their harnesses again, and Grant, at the window, found the view essentially the same as in the jugular vein. The same blue-green-violet corpuscles dominated the scene. The distant walls were more corrugated, perhaps, with the lines lying in the direction of motion.

They passed an opening.

"Not that one," said Michaels at the console, where he labored painfully over his charts. "Can you follow my markings up there, Owens?"

"Yes, doc."

"All right. Count the turnings as I mark them and then to the right here. Is that plain?"

Grant watched the subdivisions coming at briefer and briefer intervals, dividing off right and left, above and below, while the channel along which they cruised became narrower, the walls more plainly seen and closer at hand.

"I'd hate to get lost in this highway pattern," said Grant, thoughtfully.

"You can't get lost," said Duval. "All roads lead to the lungs in this part of the body."

Michaels' voice was growing monotonous. "Up and right now, Owens. Straight ahead and then, uh, fourth left."

Grant said, "No more arterio-venous fistulas, I hope, Michaels."

Michaels shrugged him off impatiently; too absorbed to say anything.

Duval said, "Not likely. To come across two by accident is asking too much of chance. Besides we're approaching the capillaries."

The velocity of the blood-stream had fallen off tremendously and so had that of the Proteus.

Owens said, "The blood-vessel is narrowing, Dr. Michaels."

"It's supposed to. The capillaries are the finest vessels of all; quite microscopic in size. Keep going, Owens."

In the light of the headbeam it could be seen that the walls, as they constricted inward, had lost their furrows and creases and were becoming smooth. Their yellowness faded into cream and then into colorlessness.

They were taking on an unmistakable mosaic pattern, broken into curving polygons, each with a slightly thickened area near the center.

Cora said, "How pretty. You can see the individual cells of the capillary wall. Look, Grant." Then, as though remembering, "How's your side?"

"It's all right. Fine, in fact. You put on a very efficient band-aid, Cora. -We're still friendly enough for the use of Cora as your name, I hope?"

"I suppose it would be rather ungrateful of me to object to that."

"And useless, too."

"How's your arm?"

Grant touched it gingerly, "Hurts like the devil."

"I'm sorry."

"Don't be sorry. Just-when the time comes-be very, very grateful."

Cora's lips tightened a bit and Grant added hurriedly, "Just my poor way of being light-hearted. How do you feel?"

"Quite myself. My side feels a little stiff, but not bad. And I'm not offended. -But listen, Grant."

"When you talk, Cora, I listen."

"Band-aids aren't the latest medical advance, you know, and they're not the universal panacea. Have you done anything about warding off infection?"

"I put on some iodine."

"Well, will you see a doctor when we get out?"

"Duval?"

"You know what I mean."

Grant said, "All right. I will."

He turned back to the sight of the cell-mosaic. The Proteus was creeping now, inching through the capillary. In the light of its headbeams, dim shapes could be seen through the cells.

Grant said, "The wall seems to be translucent."

"Not surprising," said Duval. "Those walls are less than one ten-thousandth of an inch thick. They're quite porous, too. Life depends on material getting through those walls and through the equally thin walls that line the alveoli."

"The which?"

For a moment, he looked at Duval in vain. The surgeon seemed more interested in what he was looking at than in Grant's question. Cora hastened to fill the gap.

She said, "Air enters the lungs through the trachea; you know-the windpipe. That divides, just as the blood-vessels do, into smaller and smaller tubes until they finally reach the microscopic little chambers deep in the lung, where the air that enters finds itself separated from the interior of the body only by a narrow membrane; a membrane as narrow as that of the capillaries. Those chambers are the alveoli. There are about six hundred million of them in the lungs."

"Complicated mechanism."

"A magnificent one. Oxygen leaks across the alveolar membrane and across the capillary membrane, too. It finds itself in the blood-stream and before it can leak back, the red blood corpuscles have picked it up. Meanwhile carbon dioxide wastes leak out in the other direction from blood to lungs. Dr. Duval is waiting to watch that happen. That's why he didn't answer."

"No excuses are necessary. I know what it is to be absorbed in one thing to the exclusion of another." He grinned broadly. "I'm afraid, though, that Dr. Duval's absorptions are not mine."

Cora looked uncomfortable but a cry from Owens blocked off her answer.

"Straight ahead!" he called. "Watch what's coming."

All eyes turned ahead. A blue-green corpuscle was bumping along ahead of them, scraping its edges slowly against the walls of the capillary on either side. A wave of faint straw made its appearance at the edges and then swept inward, until all the darker color was gone.

Other blue-green corpuscles making their way past them turned color likewise. The headlights were picking up only straw color ahead and the color deepened into orange-red in the distance.

"You see," said Cora, excitedly, "as they pick up the oxygen, the hemoglobin turns into oxyhemoglobin and the blood brightens to red. That will be taken back to the left ventricle of the heart now and the rich, oxygenated blood will be pumped all over the body."

"You mean we have to go back through the heart again," said Grant, in instant concern.

"Oh, no," said Cora. "Now that we're in the capillary system, we'll be able to cut across." She didn't sound very certain of it, however.

Duval said, "Look at the wonder of it. Look at the God-given wonder of it."

Michaels said, stiffly, "It's just a gas exchange. A mechanical process worked out by the random forces of evolution over a period of two billion years."

Duval turned fiercely, "Are you maintaining that this is accidental; that this marvelous mechanism, geared to perfection at a thousand points and all interlocking with clever certainty, is produced by nothing more than just the here-and-there collision of atoms?"

"That's exactly what I want to tell you. Yes." said Michaels.

At which point both, facing each other in belligerent exasperation, looked up with a snap at the sudden raucous sound of a buzzer.

Owens said, "What the devil ..:'

He flicked at a switch desperately but a needle on one of his gauges was dropping rapidly toward a red horizontal line. He shut off the buzzer and called out, "Grant!"

"What is it?"

"Something's wrong. Check the Manual right over there." Grant followed the pointing finger, moving quickly, while Cora crowded behind.

Grant said, "There's a needle in the red danger zone under something marked TANK LEFT. Obviously, the left tank's losing pressure."

Owens groaned and looked behind. "And how. We're bubbling air into the blood-stream. Grant, get up here quickly." He was shucking his harness.

Grant scrambled toward the ladder, making room as best he might for Owens to squeeze past on the way down.

Cora managed to make out the bubbles through the small rear window. She said, "Air bubbles in the blood-stream can be fatal ..."

"Not this kind," said Duval, hastily. "On our miniaturized scale we produce bubbles that are too tiny to do harm. And when they de-miniaturize they will have become too well distributed to do harm then either."

"Never mind the danger to Benes," said Michaels grimly. ''we need the air."

Owen called back to Grant, who was seating himself at the controls. "Just leave everything as it is for now, but watch for any red signal flashes anywhere on the board."

He said to Michaels as he passed him. "There must be frozen valve. I can't think of anything else." I le moved back and opened a panel with a quick wrench I one end, using a small tool he had removed from the ticket of his uniform. The maze of wires and circuit breakers was revealed in frightening complexity.

Owens' skilled fingers probed through them quickly, testing and eliminating with an ease and certainty that could have marked the ship's designer. He tripped a switch, checked it quickly and let it snap shut, then moved forward to look over the auxiliary controls underneath the windows in the bow of the ship.

"There must have been some damage outside when we scraped into the pulmonary artery, or when the arterial blood-surge hit us."

"Is the valve usable?" asked Michaels.

"Yes. It was jarred a little out of alignment, I think, and then something forced it open just now, maybe just one of the pushes of Brownian movement, it stayed that way. I've realigned it now and it will give no further trouble, only-"

"Only what," said Grant.

"I'm afraid this has torn it. We don't have enough air to complete the journey. If this were an orthodox submarine, I'd say we would have to surface to renew the air supply."

"But then what do we do now?" asked Cora.

"Surface. It's all we can do. We've got to ask to be taken out right now or the ship becomes unmaneuverable in ten minutes and we strangle in five more."

He moved to the ladder. "I'll take over, Grant. You get to the transmitter and give them the news."

Grant said, "Wait. Do we have any reserve air?"

"That was it. All of it. All gone. In fact, when that air de-miniaturizes, it will be much larger in volume than Benes . It will kill him."

"No, it won't," said Michaels. "The miniaturized molecules of the air we've lost will pass right through the tissues and out into the open. Very little will be left in the body by de-miniaturization time. Still, I'm afraid Owens is right. We can't go on."

"But wait," said Grant. "Why can't we surface?"

"I've just said . . ." began Owens, impatiently.

"I don't mean be taken out of here. I mean, real surface. There. Right there. We have blood corpuscles piling up oxygen in front of our eyes. Can't we do the same? There are only two thin membranes between ourselves and an ocean of air. Let's get it."

Cora said, "Grant's right."

"No, he isn't," said Owens. "What do you think we are? We're miniaturized, with lungs the size of a bacterial fragment. The air on the other side of those membranes is unminiaturized. Each oxygen molecule in that air is almost large enough to see, damn it. Do you think we can just take them into our lungs."

Grant looked non-plussed. "But ...'

"We can't wait, Grant. You'll have to get in touch with the control-room."

Grant said, "Not yet. Didn't you say this ship was originally meant for deep-sea research? What was it supposed to do underwater?"

"We were hoping to miniaturize underwater specimens for carriage to the surface and investigation at leisure."

"Well, then, you must have miniaturization equipment on board. You didn't pull it out last night, did you?"

"Of course we have it. But only on a small scale."

"How large scale do we need it? If we lead air into the miniaturizer, we can reduce the size of the molecules an lead them into our air tanks."

"We don't have the time for that," put in Michaels.

"If time runs out, then we'll ask to be taken out. Until, then, let's try. You've got a snorkel on board I suppose, Owens."

"Yes." Owens seemed completely confused at Grant's rapid and urgent sentences.

"And we can run such a snorkel through the capillary and lung walls without harming Benes, can't we?"

"At our size, I should certainly think so," said Duval.

"All right then, we run the snorkel from lung to ship's miniaturizer and lead a tube from miniaturizer to the air-reserve chamber. Can you improvise that?"

Owens considered for a moment, seemed to catch fire at the prospect and said, "Yes, I think so."

"All right then, when Benes inhales there'll be pressure enough to fill our tanks for us. Remember that time distortion will make our few minutes grace seem longer than it is on the unminiaturized scale. Anyway, we've got to try."

Duval said, "I agree. We must try. By all means. Now!"

Grant said, "Thanks for the support, doctor."

Duval nodded, then said, "What's more, if we're going to try this, let's not try to make a one-man job out of it. Owens had better stay at the controls, but I will come out with Grant."

"Ah," said Michaels. "I was wondering what you were after. I see now. You want a chance at exploration in the open."

Duval flushed, but Grant broke in hastily, "Whatever the motive, the suggestion is good. In fact, we had better all come out. Except Owens, of course. -The snorkel is aft, I suppose."

"In the supply and storage compartment," said Owens. He was back at the controls now, staring straight ahead. "If you've ever seen a snorkel, you won't mistake it."

Grant moved hastily into the compartment, saw the snorkel at once and reached for the packaged underwater gear.

Then he stopped in horror and shouted, "Cora!"

She was behind him in a moment. "What's the matter!"

Grant tried not to explode. It was the first time he looked at the girl without an appreciative inner comment at her beauty. For the moment, he was merely agonized. He pointed and said, "Look at that!"

She looked and turned a white face toward him, "I don't understand."

The laser over the working counter was swinging loose on one hook, its plastic cover off.

"Didn't you bother securing it?" demanded Grant.

Cora nodded wildly, "I did! I did secure it! I swear it."

"Then how could it ... "

"I don't know. How can I answer that?"

Duval was behind her, his eyes narrowed and his face flushed. He said, "What has happened to the laser, Miss Peterson?"

Cora turned to meet the new questioner. "I don't know. Why do you all turn on me? I'll test it right now. I'll check... "

"No!" roared Grant. "Just put it down and make sure it won't knock around any further. We've got to get our oxygen before we do anything else."

He began handing out the suits.

Owens had come down from the bubble. He said, "The ship's controls are locked in place. We won't be going anywhere here in the capillary anyway. My God, the laser!"

"Don't you start," screamed Cora, eyes now swimming in tears.

Michaels said, clumsily, "Now, Cora, it won't help if you break down. Later, we'll consider this carefully. -It must have been knocked loose in the whirlpool. Clearly an accident."

Grant said, "Captain Owens, connect this end of the snorkel to the miniaturizer. The rest of us will get into our suits and I hope someone shows me quickly how to get into mine. I've never tried this."

Reid said, "There's no mistake? They're not moving?"

"No, sir," came the technician's voice. "They're on the outer limits of the right lung and they're staying there."

Reid turned to Carter. "I can't explain it."

Carter stopped his angry pacing for a moment and jerked a thumb at the Time Recorder, which was reading 42. We've killed over a quarter of all the time available and we're farther from that damn clot than when we started. We should have been out by now."

"Apparently," said Reid, coldly, "we are laboring under a curse."

"And I don't feel whimsical about it, either, colonel."

"Nor do I. But what am I supposed to feel in order to satisfy you."

"At least, let's find out what's holding them up." He closed the appropriate circuit and said, "Contact the Proteus."

Reid said, "I suppose it's some sort of mechanical difficulty."

"You suppose!" said Carter, with urgent sarcasm. "I don't suppose they've just stopped for a quiet swim."