Duval looked about with exultation. "Conceive it," he said, "Inside a human body; inside an artery. -Owens! Put out the interior lights, man! Let us see God's handiwork."

The interior lights went off, but a form -of ghostly light streamed in from outside; the spotty reflection of the ship's miniaturized light beams fore and aft.

Owens had brought the Proteus into virtual motionlessness with reference to the arterial blood-stream, allowing it to sweep along with the heart-driven flow. He said, "You can remove harnesses, I think."

Duval was out of his in a bound, and Cora was with him at once. They flung themselves at the window in a kind of marveling ecstasy. Michaels rose more deliberately, threw a glance at the other two, then turned to his chart, studying it closely.

He said tightly, "Excellent precision."

"Did you think we might have missed the artery?" asked Grant.

For a moment, Michaels stared absently at Grant, Then: "Uh - no! That would have been unlikely. But we might have penetrated past a key branch point, been unable to buck the arterial current, and lost time having to plot an alternate and poorer route. As it is, the ship is just where it ought to be." His voice quavered.

Grant said, encouragingly, "We seem to be doing well so far."

"Yes." A pause, then hastily, "From this spot, we combine ease of insertion, rapidity of current, and directness of route, so that we should reach our destination with an absolute minimum of delay."

"Well, good." Grant nodded, and turned to the window. Almost at once he was lost in amazement at the wonder of it all.

The distant wall seemed half a mile away and glowed a brilliant amber in fits and sparks, for it was mostly hidden by the vast melange of objects that floated by near the ship.

It was a vast exotic aquarium they faced, one in which not fish but far stranger objects. filled the vision. Large rubber tires, the centers depressed but not pierced through, were the most numerous objects. Each was about twice the diameter of the ship, each an orange-straw color, each sparkling and blazing intermittently, as though faceted with diamond slivers.

Duval said, "The color is not quite true. If it were possible to de-miniaturize the light-waves as they leave the ship and miniaturize the returning reflection, we would be far better off. It is important to obtain an accurate reflection."

Owens said, "You're quite right, doctor, and the work done by Johnson and Antoniani indicates that this might actually be possible. Unfortunately, the technique is not yet practical and even if it were, we couldn't have adapted the ship for the purpose in a single night."

"I suppose not," said Duval.

"But even if it's not an accurate reflection," said Cora in an awed tone, "surely it has a beauty all its own. They're like soft, squashed balloons that have trapped a millions stars apiece."

"Actually, they're red blood corpuscles," said Michaels to Grant. "Red in the mass, but straw-colored individually. Those, you see are fresh from the heart, carrying their load of oxygen to the head and, particularly, the brain."

Grant continued to stare about in wonder. In addition to the corpuscles, there were smaller objects; flattened plate-like affairs were rather common, for instance. (Platelets, thought Grant, as the shapes of the objects brought up brightening memories of physiology courses in college.)

One of the platelets moved gently against the ship, so closely that Grant almost had the impulse to reach out and seize it. It flattened slowly, remained in contact for a moment, then moved away, leaving particles of itself clinging to the window-a smear that slowly washed away.

"It didn't break," said Grant.

"No," said Michaels. "Had it broken, a small clot might have formed about it. Not enough to do any damage, I hope. If we were larger, though, we might run into trouble. See that!"

Grant looked off in the direction of the pointing finger.

He saw small rod-like objects, shapeless fragments and detritus and, above all, red corpuscles, red corpuscles, red corpuscles. Then he made out the object at which Michaels was pointing.

It was huge, milky and pulsating. It was granular and inside its milkiness there were black twinkles-flashing bits of black so intense as to glow with a blinding non-light of their own.

Within the mass was a darker area, dim through the surrounding milkiness, and maintaining a steady, unwinking shape. The outlines of the whole could not be clearly made out but a milky bay suddenly extended in toward the artery wall and the mass seemed to flow into it. It faded out now, obscured by the closer objects, lost in the swirl ...

"What was that?" asked Grant.

"A white blood-cell, of course. There aren't many of those; at least, not compared to the red corpuscles. There are about 650 reds for every white. The whites are much bigger, though, and they can move independently. Some of them can even work their way out of the blood-vessels altogether. They're frightening objects, seen on this scale of size. That's about as close as I want to be to one."

"They're the body's scavengers, aren't they?"

"Yes. We're bacterial-sized but we have a metal skin and not a mucopolysaccharide cell-wall. I trust the white cells can tell the difference and that as long as we do no damage to the surrounding tissues, they won't react to us."

Grant tried to withdraw his too-particular attention from individual objects and attempted to absorb the panorama as a whole. He stepped back and narrowed his eyes.

It was a. dance! Each object quivered in its position. The smaller the object, the more pronounced the quiver. It was like a colossal and unruly ballet in which the choreographer had gone mad and the dancers were caught in the grip of an eternally insane tarantella.

Grant closed his eyes. "Feel it? The Brownian motion, I mean."

Owens answered, "Yes, I feel it. It's not as bad as I thought it would be. The blood-stream is viscous, much more viscous than the saline solution we were in; and the high viscosity damps out the motion."

Grant felt the ship move under his feet, first this way, then that, but only soggily, not sharply as had been true while they were still in the hypodermic. The protein content of the fluid portion of the blood, the "plasma proteins" (the phrase came swimming to Grant out of the past) cushioned the ship.

Not bad at all. He felt cheered. Perhaps all would be well yet.

Owens said, "I suggest you all return to your seats now. We will be approaching a branch in the artery soon and I am going to move over to one side."

The others settled themselves into their seats, still watching their surroundings in absorption.

"I think it's a shame that we'll only have a few minutes for this," said Cora. "Dr. Duval, what are those?"

A mass of very tiny structures, clinging together and forming a tight spirally-shaped pipe, passed by. Several more followed, each expanding and contracting as it went.

"Ah," said Duval, "I don't recognize that."

"A virus, perhaps," suggested Cora.

"A little too large for virus, I think, and certainly like none I've seen. -Owens, are we equipped to take samples?"

Owens said, "We can get out of the ship, if we have to, doctor, but we can't stop for samples."

"Come now, we may not have this chance again." Duval rose testily to his feet. "Let's get a piece of that into the ship. Miss Peterson, you ..."

Owens said, "This ship has a mission, doctor."

"It doesn't matter to ..." began Duval, but then broke off at the firm grip of Grant's hand on his shoulder.

"If you don't mind, doctor," said Grant, "let's not argue about this. We have a job to do and we won't stop to pick up anything or turn aside to pick up anything or as much as slow down to pick up anything. I take it you understand that and will not raise the subject again."

In the uncertain flickering light reflected from the arterial world outside, Duval was clearly frowning.

"Oh, well," he said, ungraciously, "they've gotten away anyhow."

Cora said, "Once we complete this job, Dr. Duval, there will be methods developed for miniaturization for indefinite intervals. We can then take part in a real exploration."

"Yes, I suppose you're right."

Owens said, "Arterial wall to the right.

The Proteus had made a long, sweeping curve and the wall seemed about a hundred feet away, now. The somewhat corrugated amber stretch of endothelial layer that made up the inner lining of the artery was clearly visible in all its detail.

"Hah," said Duval, "what a way to check on athero-sclerosis. You can count the plaques."

"You could peel them off, too, couldn't you?" asked Grant.

"Of course. Consider the future. A ship can be sent through a clogged arterial system, loosening and detaching the sclerotic regions, breaking them up, boring and reaming out the tubes. Pretty expensive treatment, however."

"Maybe it could be automated eventually," said Grant. "Perhaps little housekeeping robots can be sent in to clean up the mess. Or perhaps every human being in early manhood can be injected with a permanent supply of such vessel-cleansers. Look at the length of it."

They were closer still to the arterial wall now, and the ride was growing rougher in the turbulence near it. Looking ahead, though, they could see the wall stretching ahead for what seemed unbroken miles before veering off.

Michaels said, "The circulatory system, counting all its vessels to the very smallest, is as I told you earlier, a hundred thousand miles long, if it were strung out in one long line."

"Not bad," said Grant.

"A hundred thousand miles in the unminiaturized scale. On our present scale, it is," he paused to think, then said, "over three trillion miles long-half a light year. To travel through every one of Benes' blood-vessels in our present state would be almost the equivalent of a trip to a star."

He looked about haggardly. Neither their safety thus far, nor the beauty of their surroundings, seemed to have consoled him much.

Grant strove to be cheerful. "At least the Brownian motion isn't at all bad," he said.

"No," said Michaels. Then, "I didn't come off too well a while ago when we first discussed Brownian motion."

"Neither did Duval just now in the matter of samples. I don't think any of us are doing really well."

Michaels swallowed. "That was typically single-minded of' Duval to want to stop for specimens."

He shook his head and turned to the charts on the curving desk against one wall. It, and the moving dot of light upon it, was a duplicate of the much larger version in the control tower, and of the smaller version in Owens' bubble. He said,

"What's our speed, Owens?"

"Fifteen knots, our scale,"

"Of course, our scale," said Michaels, pettishly. He lifted his slide-rule from its recess and made a rapid calculation. "We'll be at the branch in two minutes. Keep the wall at its present distance when you turn. That will bring you safely into the middle of the branch and you can then move smoothly into the capillary net without further branching. Is that clear?"

"All clear!"

Grant waited, watching always through the window. For a moment, he caught the shadow of Cora's profile and watched that, but the view from the window overpowered even his study of the curve of her chin.

Two minutes? How much would that be! Two minutes as his miniaturized time-sense would make it out to be? Or two minutes by their Time Recorder. He twisted his head to look at it. It read 56 and, as he watched, it blanked out and then, very deliberately, 55 appeared dimly and darkened.

There was a sudden wrench and Grant was nearly thrown out of his seat.

"Owens!" he cried out. "What happened?"

Duval said, "Have we struck something?"

Grant struggled his way toward the ladder and managed to climb up. He said, "What's wrong."

"I don't know." Owens' face was a contorted mask of effort. "The ship won't handle."

Michaels' voice came up tensely, "Captain Owens, correct your course. We're approaching the wall."

"I know that," gasped Owens. "We're in some sort of current."

Grant said, "Keep trying. Do your best."

He swung down and, with his back against the ladder, trying to hold steady against the heaving of the ship, said, "Why should there be a cross-current here? Aren't we going along with the arterial flow?"

"Yes," said Michaels, emphatically, his face waxen in its pallor, "there can't be anything to force us sideways like this." He pointed outward at the arterial wall, much closer now and still approaching. "There must be something wrong with the controls. If we strike the wall and damage it, a clot may form about us and fix us there, or the white cells may respond."

Duval said, "But this is impossible in a closed system. The laws of hydrodynamics..."

"A closed system?" Michaels' eyebrows shot upward. With an effort, he staggered his way to his charts, then moaned, "It's no use, I need more magnification and I can't get it here. -Watch it, Owens, keep away from the wall."

Owens . shouted back: "I'm trying. I tell you there's a current that I can't fight."

"Don't try to fight it directly, then," cried Grant. "Give the ship its head and confine yourself to trying to keep its course parallel to the wall."

They were close enough now to see every detail of the wall. The strands of connective tissue that served as its chief support were like trusses, almost like Gothic arches, yellowish in color and glimmering with a thin layer of what seemed a fatty substance.

The connective strands stretched and bowed apart as though the whole structure were expanding, hovered a moment, then moved together again, the surface between the trusses crinkling as they closed in. Grant did not need to ask to realize he was watching the arterial wall pulse in time to the beat of the heart.

The buffeting of the ship was growing worse. The wall was closer still and beginning to look ragged. The connective strands had worked loose in spots, as though they themselves had been withstanding a raging torrent for much longer than ever the Proteus had, and were beginning to buckle under the strain. They swayed like cables of a gigantic bridge, coming up to the window and sliding past wetly, giving off their sparkling yellow color in the jumping beam of the ship's headlights.

The approach of the next made Cora scream in shrill terror.

Michaels shouted, "Watch out, Owens."

Duval muttered, "The artery is damaged."

But the current swept around the living buttress and carried the ship with it, throwing it into a sickening lurch that piled everyone helplessly against the left wall.

Grant, his left arm having withstood a painful slam, caught at Cora with his other and managed to keep her upright. Staring straight ahead he was trying to make sense out of the sparkling light.

He shouted, "Whirlpool! Get into your seats, all of you. Strap yourselves in."

The formed particles, from red corpuscles down, were virtually motionless outside the window for the moment as all were caught in the same whirling current while the wall blurred into yellow featurelessness.

Duval and Michaels struggled to their seats and wrenched at their harnesses.

Owens shouted, "Some sort of opening dead ahead." Grant said urgently to Cora, "Come on. Pull yourself into your seat."

"I'm trying," she gasped.

Desperately, all but unable to keep his footing against the sharp swaying of the ship, Grant pushed her down and then reached for her harness.

It was quite too late. The Proteus was caught up in the whirlpool now and was lifted upward and round with the force of a carnival whip."

Grant managed to seize a stanchion by a reflex grab and reached out for Cora. She had been hurled to the floor. Her fingers curled over the arm of her chair, and strained uselessly.

They were not going to hold, Grant knew, and he reached for her desperately, but he was a good foot short. His own arm was slipping from the stanchion, as he reached for her.

Duval was struggling uselessly in his own seat, but centrifugal pressure had him pinned. "Hold on, Miss Peterson. I will try to help."

With an effort he had reached his harness, while Michaels watched, eyes turning toward them in frozen helplessness, and Owens, pinned in his bubble, remained completely out of the picture.

Cora's legs lifted from the ground in response to the centrifugal effect. "I can't ...

Grant, out of sheer lack of alternatives, released his own hold. He slithered across the floor, hooked a leg around the base of a chair with a blow that numbed it, managed to transfer his left arm there, too, and with his right caught Cora about the waist as her own grip gave way.

The Proteus was turning faster, now, and seemed to be angling downward. Grant could stand the strained position of his body no longer and his leg flipped away from the chair leg. His arm, already bruised and painful by earlier contact with the wall, took the additional strain with an ache that made it feel as though it were breaking. Cora clutched at his shoulder and seized the material of his uniform with vise-like desperation.

Grant managed to grunt out, "Has anyone-figured out what's happening?"

Duval, still struggling futilely with his harness, said, "It's a fistula-an arterio-venous fistula."

With an effort, Grant raised his head and looked out the window once more. The damaged arterial wall came to an end dead ahead. The yellow sparkling ceased and a blackened ragged gap was visible. It reached as high and as low as his restricted vision could make out and red corpuscles, as well as other objects, were vanishing into it. Even the occasional terrifying blobs of white cells which appeared sucked rapidly through the hole.

"Just a few seconds," gasped Grant. "Just a few, Cora." He was telling it to himself, to his. own aching, bruising arm.

With a final vibration that nearly stunned Grant with the agony he had to endure, they were through, and slowing, slowing, into sudden calm.

Grant released his hold and lay there, panting heavily. Slowly, Cora managed to get her legs under her and stand up.

Duval was free now. "Mr. Grant, how are you?" He knelt down at Grant's side.

Cora knelt down, too, touching Grant's arm gently, venturing to try to knead it. Grant grimaced in pain, "Don't touch it!"

"Is it broken?" asked Duval.

"I can't tell." Gingerly and slowly, he tried to bend it; then caught his left biceps in his right palm, and held it tightly. "Maybe not. But even if it isn't, it will be weeks before I can do that again."

Michaels had also risen. His face was twisted almost unrecognizably with relief. "We made it. We made it. We're in one piece. How is it, Owens?"

"In good order, I think," said Owens. "Not a red light on the panel. The Proteus took more than it was designed to take and it held." His voice reflected a fierce pride in himself and his ship.

Cora was still brooding helplessly over Grant. She said, in shock, "You're bleeding!"

"I am? Where?"

"Your side. The uniform is showing blood."

"Oh, that. I had a little trouble on the Other Side. It' just a matter of replacing a band-aid. Honestly, it's nothing Just blood."

Cora looked anxious, then unzipped his uniform. "Sit up,' she said. "Please try to sit up." She slipped an arm under his shoulders and struggled him upright, then pulled the uniform down over his shoulders with practiced gentleness.

"I'll take care of it for you," she said. "And thank you., It seems foolishly inadequate, but thank you."

Grant said, "Well, do the same for me sometime, wilt you? Help me into my chair, will you?"

He struggled to his feet now, Cora helping him on one side, Michaels on the other. Duval, after one glance at them, had limped to the window.

Grant said, "Now what happened?"

Michaels said, "An arterio-ven . . . Well, put it this way. An abnormal connection existed between an artery and a small vein. It happens sometimes, usually as the result of physical trauma. It happened to Benes at the time he was hurt in the, car, I suppose. It represents an imperfection, a kind of inefficiency, but in this case not a serious one. It's microscopic; a tiny eddy."

"A tiny eddy. This!"

"On our miniaturized scale, of course, it's a gigantic whirlpool."

"Didn't it show up on your charts of the circulatory system, Michaels?" asked Grant.

"It must have. I could probably find it here on the ship's chart, if I could magnify it sufficiently. The trouble is my initial analysis had to be made in three hours and I missed it. I have no excuse."

Grant said, "All right, it just means some lost time. Plot out an alternate route and get Owens started. What's the time, Owens?" He looked at the Time Recorder automatically as he asked. He read: 52, and Owens said, "Fifty-two."

"Plenty of time," said Grant.

Michaels was staring at Grant with raised eyebrows. He said, "There's no time, Grant. You haven't grasped what's happened. We're finished. We've failed. We can't get to the clot anymore, don't you understand? We must ask to be removed from the body."

Cora said in horror, "But it will be days before the ship can be miniaturized again. Benes will die."

"There's nothing to be done. We're heading into the jugular vein now. We can't go back through the fissure for we couldn't buck that current, even when the heart is in the iastolic stage, between beats. The only other route, the one in which we follow the venous current, leads through the heart, which is clear suicide."

Grant said, numbly, "Are you sure?"

Owens said, in a cracked, dull voice, "He's right, Grant. I he mission has failed."