The four of them,. Michaels, Duval, Cora, , and Grant, were in 'their swim-suits now - form-fitting, comfortable, and an antiseptic white. Each had oxygen cylinders strapped to he back, a flashlight on the foreheads, fins on the feet and a radio transmitter and receiver at mouth and ear respectively.

"It's a form of skin-diving," said Michaels, adjusting the head-gear, "and I've never gone skin-diving. To have the first try at it in someone's blood-stream . . .'

The ship's wireless tapped urgently.

Michaels said, "Hadn't you better answer that?"

"And get into a conversation?" said Grant, impatiently. "There'll be time for talk when we're done. Here, help me."

Cora guided the plastic-shielded helmet over Grant's head and snapped it into place.

Grant's voice, transmuted at once into the faintly distorted version that comes over a small radio, sounded in her ear, "Thanks, Cora."

She nodded at him-dolefully.

Two by two they used the escape hatch and precious air had to be consumed by forcing blood plasma out of the hatch each time.

Grant found himself paddling in a fluid that was not even as clear as the water one would find on the average polluted beach. It was full of floating debris, flecks and bits of matter. The Proteus filled half the diameter of the capillary and past it red blood corpuscles nudged their way along with the periodic easier passage of the smaller platelets.

Grant said uneasily, "If platelets break against the Proteus, we may form a clot."

"We may," said Duval, "but it won't be dangerous here; not in a capillary."

They could see Owens within the ship. He lifted his head and revealed an anxious face. He nodded and moved his hand without enthusiasm, trying to dodge and turn so as to be visible between and among the endlessly passing corpuscles. He put on the head-gear of his own swim-suit and spoke into its transmitter.

He said, "I think I've got it arranged here. Anyway, I've done my best. Are you ready to have me release the snorkel?"

"Go ahead," said Grant.

It came out of the special release hatch like a cobra coming out of a fakir's basket at the sound of the pipes. Grant seized it.

Michaels said, "Oh, heck," in a sort of whisper. Then, more loudly, and in a tone that seemed saturated with chagrin, he said, "Consider how narrow the bore of that snorkel is, all of you. It looks as big around as a man's arm, but how big is a man's arm on our scale?"

"What of it?" said Grant, shortly. He had a firm grip on the snorkel now and he put his back into moving with it toward the capillary wall, disregarding the soreness of his left biceps. "Grab hold, will you, and help pull."

Michaels said, "There's no point to it. Don't you understand? It should have occurred to me sooner, but the air won't go through that thing."

"What?"

"Not quickly enough. Unminiaturized air molecules are quite big compared to the opening in that snorkel. Do you expect air to leak through a tiny tube barely large enough to see through a microscope."

"The air will be under lung-pressure."

"So what? Ever hear of a slow leak in an automobile tire. The hole through which air leaks in such a tire is' probably no smaller than that and is under considerably more pressure than the lung can generate, and it's a slow leak." Michaels grimaced lugubriously. "I wish I had thought of this sooner."

Grant roared, "Owens!"

"I hear you. Don't crack every ear-drum in existence."

"Never mind hearing me. Did you hear Michaels?"

"Yes, I have."

"Is he right? You're the nearest thing to a miniaturization expert we have. Is he right?"

"Well, yes and no," said Owens.

"And what does that mean?"

"It means, yes, the air will go through the snorkel only very slowly unless it is miniaturized and, no, we need not worry if I can succeed in miniaturizing it. I can extend the field through the snorkel and miniaturize the air on the other side and suck that through by ..."

"Won't such a field-extension affect us?" put in Michaels.

"No, I'll have it set for a fixed maximum of miniaturization and we're there already."

"How about the surrounding blood and lung tissue?" asked Duval.

"There's a limit to how sharply selective I can make the field," admitted Owens. "This is only a small miniaturizer I have here but I can confine it to gas. There's bound to be some damage, however. I just hope it won't be too much."

"We'll have to chance it, that's all," said Grant. "Let's get on with it. We can't take forever."

With four pairs of arms encircling the snorkel and four pairs of legs pumping away, it reached the capillary wall.

For a moment, Grant hesitated. "We're going to have to cut through. -Duval!"

Duval's lips curved in a small smile. "There's no need to call on the surgeon. At this microscopic level, you would do as well. There is no skill needed."

He drew a knife from a small scabbard at his waist, and looked at it. "It undoubtedly has miniaturized bacteria on it. Eventually, they will de-miniaturize in the blood-stream but the white cells will take care of them, then. Nothing pathogenic in any case, I hope."

"Please get on with it, doctor," said Grant, urgently.

Duval slashed quickly with his knife between two of the cells that made up the capillary. A neat slit opened. The thickness of the wall might be a ten-thousandth of an inch in the world generally, but on their own miniaturized scale the thickness amounted to several yards. Duval stepped into the slit and forced his way through, breaking stands of inter-cellular cement and cutting further. The wall was perforated at last and the cells drew apart, like the lips of a gaping wound.

Through the wound could be seen another set of cells, at which Duval slashed neatly and with precision.

He returned and said, "It's a microscopic opening. There'll be no loss of blood to speak of."

"No loss at all," said Michaels emphatically. "The leakage is the other way."

And, indeed, a bubble of air seemed to bulge inward at the opening. It bulged further and then stopped. Michaels put his hand to the bubble. A portion of its surface pushed inward, but the hand did not go through

"Surface tension!" he said.

"What now?" demanded Grant.

"Surface tension, I tell you. At any liquid surface there is a kind of skin effect. To something as large as a human being, an unminiaturized human being, the effect is too small to be noticed, but insects can walk on water surfaces because of it. In our miniaturized state, the effect is even stronger. We may not be able to get beyond the barrier."

Michaels drew his knife and plunged it into the fluid-gas interface as, a moment before, Duval had operated on the cells. The knife forced the interface forward into a point, then broke through.

"It's like cutting thin rubber," said Michaels, panting a bit. He sliced downward and an opening appeared briefly but closed almost at once, healing itself.

Grant tried the same thing, forcing his hand through the opening before it closed. He winced a bit as the water molecules closed in.

"It's got a grip on it, you know."

Duval said somberly, "If you calculated the size of those water molecules on our scale you'd be astonished. You could make them out with a hand lens. In fact . . ."

Michaels said, "In fact, you're sorry you didn't bring a hand lens. I've got news for you, Duval, you wouldn't see much. You would magnify the wave properties as well as the particle properties of atoms and subatomic particles. Anything you see, even by the reflection of miniaturized light, would be too hazy to do you much good."

Cora said, "Is that why nothing really looks sharp? I thought it was just because we were seeing things through blood plasma."

"The plasma is a factor, certainly. But in addition, the general graininess of the universe becomes much larger as we become much smaller. It's like looking really closely at an old-fashioned newspaper photograph. You see the dots more clearly and it becomes hazy."

Grant was paying little attention to the conversation. His arm was through the interface and with it he was tearing away to make room for his other arm and his head.

For a moment the fluid closed about his neck and he felt strangled.

"Hold my legs, will you?" he called.

Duval said, "I've got them."

Half his body was through now and he could look through the crevice Duval had made through the walls.

"All right. Pull me down again." He came down and the interface closed behind him with a popping sound.

He said, "Now let's see what we can do about the snorkel. Heave-ho."

It was quite useless. The blunt end of the snorkel made not a dent on the tightly-knit skin of water molecules on the air bubble. Knives cut that skin to shreds so that parts of the snorkel got through but the instant the interface was left- to itself, surface tension would reassert itself and the snorkel would pop out.

Michaels was panting with effort. "I don't think we're going to make it."

"We've got to," said Grant. "Look, I'm getting in; all the way in. When you push the snorkel through, I'll grab whatever part makes it and pull. Between pushing and pulling ..."

"You can't go in there, Grant," said Duval. "You'll be sucked in and lost."

Michaels said, "We can use a lifeline. Right here, Grant." He indicated the neatly nested line at Grant's left hip. -Duval, take this back to the ship and attach it and we'll get Grant through."

Duval took the end handed him, rather uncertainly, and swam back toward the ship.

Cora said, "But how will you get back? Suppose you can't push through the surface tension again?"

"Sure, I will. Besides, don't confuse the situation by taking up problem number 2 while problem number 1 is still with us."

Owens, within the ship, watched tensely as Duval swam up. "Do you need another pair of hands out there," he asked.

Duval said, "I don't think so. Besides, your pair are needed at the miniaturizer." He hitched the safety line to a small ring on the ship's metal skin and waved his arm. "OK, Grant."

Grant waved back. His second penetration of the interface was more quickly done for he had the knack now., First a slit, then one arm (ouch, the bruised bicep), then the other; then a strenuous push against the interface with his arms, and a kick with his finned legs and he popped out like watermelon seed from between finger and thumb.

He found himself between the two sticky walls of the intercellular slit. He looked down at Michaels' face, clearly visible but somewhat distorted through the curve of the interface.

"Push it through, Michaels.

Through the interface, he could make out a thrashing of limbs, the swing of an arm holding a knife. And then the blunt metal end of the snorkel made a partial appearance. Grant knelt and seized it. Bracing his back against one side of the crevice and his feet against the other, he pulled. The interface rose with it, clinging to it all about. Grant worked his way upward ahead of it, gasping out, "Push! Push!"

It broke through, clear at last. Inside the tube of the snorkel was fluid, clinging motionlessly.

Grant said, "I'm going to get it up through now, into the alveolus."

Michaels said, "When you get to the alveolus, be careful. I don't know how you'll be affected by inhalation and exhalation but you're liable to find yourself in a hurricane."

Grant was moving upward, yanking at the snorkel as he found purchases in the soft yielding tissue for gripping fingers and kicking feet.

His head rose beyond the alveolar wall and quite suddenly, he was in another world. The light from the Proteus penetrated through what seemed to him a vast thickness of tissue and in its muted intensity, the alveolus was a tremendous cavern, with walls that glinted moistly and distantly.

About him were crags and boulders of all sizes and colors, sparkling iridescently, as the inefficient reflection of miniaturized light gave them all a spuriously beautiful luster. He could see now that the edges of the boulders remained hazy even without the presence of slowly swirling fluid to account for it.

Grant said, "This place is full of rocks."

"Dust and grit, I imagine," came Michaels' voice. "Dust and grit. The legacy of living in civilization, of breathing unfiltered air. The lungs are a one-way passage; we can take dust in but there's no way of pushing it out again."

Owens put in, "Do your best to hold the snorkel over your head, will you? I don't want any fluid plugging it. -Now!"

Grant heaved it high. "Let me know when you've had enough, Owens," he panted.

"I will"

"Is it working?"

"It sure is. I have the field adjusted strobophilically so that it acts in rapid spurts according to the . . . Well, never mind. The point is the field is never on long enough to affect liquids or solids significantly but it is miniaturizing gases at a great rate. I've got the field extended far beyond Benes into the atmosphere of the operating room."

"Is that safe?" asked Grant.

"It's the only way we can get enough air. We have to have thousands of times as much air as all of Benes' lungs contain, and miniaturize it all. Is it safe? Good Lord, man, I'm sucking it in right through Benes' tissues without even affecting his respiration. Oh, if I only had a larger snorkel." Owens sounded as gay and excited as a youngster on his first date.

Michaels' voice in Grant's ear said, "How are you being affected by Benes' breathing?"

Grant looked quickly at the alveolar membrane. It seemed stretched and taut under his foot, so he guessed he was witnessing the slow, slow end of an inhalation. (Slow in any case; slower because of the hypothermia; slower still because of the time-distortion induced by miniaturization.)

"It's all right;" he said. "No effect at all."

But now a low rasp made itself felt in Grant's ear. It grew slowly louder and Grant realized an exhalation was beginning. He braced himself and held on to the snorkel.

Owens said jubilantly, "This is working beautifully. Nothing like this has ever been done before."

The motion of air was making itself felt about Grant, as the lungs continued their slow but accelerating collapse and the rasp of exhalation grew louder. Grant felt his legs lifting from the alveolar floor. On an ordinary scale, he knew, the air current in the alveolus was indetectably gentle but on the miniaturized scale, it was gathering into a tornado.

Grant gripped the snorkel in desperation, flinging both arms about it and both legs. It strained upward and so did he. The very boulders-dust-boulders-came loose and rolled slightly.

The wind slowly died then as the exhalation came to its slow halt and Grant released the snorkel with relief. He said, "How's it doing, Owens?"

"Almost done. Hang on for a few seconds, will you, Grant?"

"Okay."

He counted to himself: twenty-thirty-forty. The inhalation was starting and air molecules were impinging upon him. The alveolar wall was stretching again and he stumbled to his knees.

"Full!" cried Owens. "Get back in."

"Pull down on the snorkel," yelled Grant. "Quickly. Before another exhalation comes."

He pushed downward and they pulled. Difficulty arose only when the lip of the snorkel approached the interface. It held tight there for a moment as though in a vice-and then pulled through with a small thunderclap of joining surface film.

Grant had watched too long. With the snorkel safely in, he made a motion as though to plunge into the crevice and through the interface at its bottom, but the beginning of the exhalation surrounded him with wind and caused him to stumble. For a moment, he found himself wedged between two dust-boulders and in wrenching free found that he had slightly barked one shin. (Hurting one's shin against a particle of dust was surely something to tell one's grandchildren.)

Where was he? He shook his lifeline, freeing it from some snag on one of the boulders, and pulled it taut. It would be easiest to follow it back to the crevice.

The lifeline snaked over the top of the boulder and Grant, bracing his feet against it, climbed rapidly upward. The strengthening exhalation helped him do so and there was scarcely any sensation of effort in the upward striving. Then still less. The crevice, he knew, was just the other side of the boulder and he might have gone around it but for the fact that the exhalation made the route over it the simpler and because (why not admit it?) it was more exciting this way.

The boulder rolled beneath his feet, at the peak of the exhalation wind, and Grant lifted free. For the moment he found himself high in the air, the crevice just ' beyond, exactly where he had expected it to be. It was only necessary to wait a second or two for exhalation to cease and he would lunge quickly for the crevice, the blood-stream, and the ship.

And even as he thought so, he felt himself sucked wildly upward, the lifeline following and snaking entirely free of the crevice which, in half a moment, was lost to sight.

The snorkel had been pulled out of the alveolar crevice and Duval was snaking it back to the ship.

Cora said anxiously, "Where's Grant?"

"He's up there," said Michaels, peering.

"Why doesn't he come down?"

"He will. He will. It takes some negotiating, I imagine." He peered upward again. `Benes is exhaling. Once that's done, he'll have no trouble."

"Shouldn't we grab hold of his lifeline and pull him in."

Michaels threw out an arm and forestalled her. "If you do that and yank just as an inhalation starts, forcing him downward, you may hurt him. He'll tell us what to do if he needs help."

Restlessly, Cora watched and then broke away toward the lifeline. "No," she said, "I want to ..."

And at that moment, the lifeline twitched and snaked upward, its end flashing past, and out through the opening.

Cora screamed, and kicked herself desperately toward the opening.

Michaels pursued. "You can't do anything," he panted. "Don't be foolish."

"But we can't leave him in there. What will happen to him?"

"We'll hear from him by his radio."

"It may be broken."

"Why should it be?"

Duval joined them. He said, chokingly. "It came loose as I watched. I couldn't believe it."

All three gazed upward helplessly.

Michaels called, tentatively, "Grant! Grant! Do you receive me?"

Grant went tumbling and twisting upward. His thoughts were as jumbled as his line of flight. I won't get back, was the dominant thought. I won't get back. Even if I stay in radio contact, I can't come in on the beam.

Or could he?

"Michaels," he called. "Duval."

There was nothing at first, then a faint crackling noise in his ears; and a distorted squawk that might have been "Grant!"

He tried again, "Michaels! Do you hear me? Do you hear me?"

Again the squawking. He could not make out anything.

Somewhere within a tense mind there came a calm thought, as though his intellect had found time to make a serene note. Although miniaturized light-waves were more penetrating than the ordinary kind, miniaturized radio-waves seemed less penetrating.

Very little was known about the miniaturized state, apparently. It was the misfortune of the Proteus and her crew to be pioneers into a realm that was literally unknown; surely a fantastic voyage if ever there was one.

And within that voyage, Grant was now on a fantastic subvoyage of his own; blown through what seemed miles of space within a microscopic air-chamber in the lung of a dying man.

His motion was slowing. He had reached the top of the alveolus and had moved into the tubular stalk from which it was suspended. The far-off light of the Proteus was dim indeed. Could he follow the light, then? Could he try to move in whatever direction it seemed stronger.

He touched the wall of the tubular stalk and stuck there, like a fly on flypaper. And with no more sense than the fly, at first, he wriggled.

Both legs and an arm were stuck to the wall, in no time. He paused and forced himself to think. Exhalation was complete but inhalation would be beginning. The air current would be forcing him downward. Wait for it!

He felt the wind begin and heard the rushing noise. Slowly, he pulled his clinging arm loose and bent his body out into the wind. It pushed him downward and his legs came loose, too.

He was falling now, plummeting downward from a height which, on his miniaturized scale, was mountainous. From the unminiaturized point of view, he knew he must be drifting downward in feathery fashion, but as it was, what he experienced was a plummet. It was a smooth drop, non-accelerated, for the large molecules of air (almost large enough to see, Michaels had said) had to be pushed to one side as he fell and that took the energy that would otherwise have gone into acceleration.

A bacterium, no larger than he, could fall this distance safely, but he, the miniaturized human, was made up of fifty trillion miniaturized cells and that complexity made him fragile enough, perhaps, to smash apart into miniaturized dust.

Automatically, as he thought that, he threw up his hands in self-defense when the alveolar wall came whirling close. He felt the glancing contact; the wall gave soggily and he bounced off after clinging for a moment. His speed of fall had actually slowed.

Down again. Somewhere below, a speck of light, a bare pin-point had winked on as he watched. He kept his eye fixed on that with a wild hope.

Still down. He kicked his feet wildly to avoid an outcropping of dust-boulders; narrowly missed and struck a spongy area again. Again falling. He thrashed wildly in an attempt to move toward the pin-point of light as he fell and it seemed to him he might have succeeded somewhat. He wasn't sure.

He came rolling down the lower slope of the alveolar surface at length. He flung his lifeline around an outcropping and held on just barely.

The pin-point of light had become a small glare, some fifty feet away, he judged. That must be the crevice and close though it was, he couldn't possibly have found it without the guidance of the light.

He waited for the inhalation to cease. In the short interval of time before exhalation, he had to make it there.

Before inhalation had come to a complete halt, he was slipping and scrambling across the space between. The alveolar membrane stretched in the final moment of inhalation and then, hovering at that point for a couple of seconds, began to lose its tension as the first instants of gathering exhalation began.

Grant threw himself down the crevice which was ablaze with light. He kicked at the interface which rebounded in rubbery fashion. A knife slit through; a hand appeared and seized his ankle in firm grip. He felt the pull downward just as the upward draft was beginning to make itself felt about his ears.

Down he went with other hands adding to the grip on his legs and he was back in the capillary. Grant breathed in long, shuddering gasps. Finally, he said, "Thanks! I followed the light! Couldn't have made it otherwise."

Michaels said, "Couldn't reach you by radio."

Cora was smiling at him. "It was Dr. Duval's idea. He had the Proteus move up to the opening and shine its headlight directly into it. And he made the opening bigger, too.

Michaels said, "Let's get back in the ship. We've lost just about all the time we can afford to lose."