His first impulse was to expect redness. What else?

He peered out, squinting his eyes slightly, but could see nothing, even in the gleaming light of the ship. He might as well have been in a rowboat, drifting down the calm surface of a pond on a dark and cloudy night.

Morrison's thoughts suddenly veered. In the absolute sense, the light within the ship had the wavelength of gamma rays - and very hard gamma rays at that. Yet the wavelengths were the result of miniaturizing ordinary visible light and to the equally miniaturized retinas and optic lobes of the people within the ship they were still light rays and had the property of light rays.

Outside, just beyond the hull of the ship, where the miniaturization field ended, the miniaturized photons enlarged to ordinary light-wave photons and those that were reflected back to the ship were miniaturized again when the field boundary was crossed. The others might be accustomed to this paradox-ridden situation, but to Morrison the attempt to grasp the effect of a miniaturized bubble within a sea of normality was dizzying. Was the boundary visible, marking off the miniaturized from the normal? Was there a discontinuity somewhere?

Following his line of thought, he whispered to Kaliinin, who was bent over her instrument, "Sophia, when our light leaves the miniaturization field and expands, it must give off heat energy, and when it's reflected back into the ship it must absorb energy in order to be miniaturized and the energy must come from us. Am I right?"

"Perfectly, Albert," said Kaliinin without looking up. "Our use of light results in a small but steady loss of energy, but our motors can supply that. It is not a significant drain."

"And are we really in the bloodstream?"

"Never fear. We are. Natalya will probably dim the internal lights in a while and you'll see the outside more clearly then."

Almost as though that were a signal, Boranova said, "There! Now we can relax for a few moments." The lights dimmed.

At once, objects outside the ship came dimly into view. He could not make them out clearly yet, but they were immersed in something heterogeneous, something with objects floating in it, as would be true of blood.

Morrison stirred uneasily, straining at the constraint of his seat belt. He said, "But if we are in the bloodstream, which is at a temperature of thirty-seven degrees Celsius, we'll -"

"Our temperature is conditioned. We'll be quite comfortable," said Kaliinin. "Really, Albert, we've thought of these things."

"Perhaps you have," said Morrison, slightly offended, "but I haven't been privy to those thoughts, have I? How can you condition the temperature when you don't have a cold sink?"

"We don't have one here, but there's outer space, isn't there? The microfusion motors give off a thin drizzle of subatomic particles which, under miniaturized conditions, have a mass of very nearly zero. They therefore travel at virtually the speed of light, penetrating matter as easily as neutrinos do and carrying off energy with them. In less than a second they are in outer space, so that the effect is of transferring heat from within the ship into outer space and we keep cool. Do you see?"

"I see," muttered Morrison. It was ingenious - but perhaps obvious, after all, to those used to thinking in terms of miniaturization.

Morrison noticed that the controls of the ship, immediately under Dezhnev's hands, were luminous, as were the instruments before Kaliinin. He struggled to raise himself in his seat and managed to see a corner of the computer screen in front of Konev. It contained what Morrison thought might be a map of the circulatory system of the neck. For a moment, before his body ceased its fight against the webbing of the belt and he sank down into his seat again, he saw a small red dot on the screen, which, he deduced, was a device to mark the position of the ship in the left internal carotid artery.

He was panting a little from his effort and had to wait a few moments to regain control of his breath. The recess in which his own computer rested was illuminated and he shielded that bit of light from his face by raising his left hand. Then he looked out.

Far in the distance, Morrison could see something that looked like a wall, a barrier of some sort. It receded, then approached, then receded again, over and over, rhythmically. Automatically, he looked at his watch for a few seconds. It was clearly the pulsation of the arterial wall.

He said to Kaliinin in a low voice, "Obviously the passage of time is not affected by miniaturization. At least the pulsation of the heart is - just what it ought to be, even though I view it with miniaturized eyes and time it with a miniaturized watch."

It was Konev who answered. "Time isn't quantized apparently, or at least it isn't affected oy the miniaturization field, which may be the same thing. That's convenient. If we had to take a shifting time flow into account, things might become unbearably complicated."

Morrison silently agreed and turned his thoughts in other directions.

If they were inside an artery, and if the ship were merely being swept forward by the current, the forward movement would have to be in spurts, one spurt for each contraction of the distant heart (the very distant heart - on the scale of their present size). And if that were so, he ought to feel those spurts of motion.

He closed his eyes and tried to hold as still as possible, to move not at all except for the trembling of the Brownian motion - which, after all, he could in no way control.

Ah, he could feel it. A slight but distinct push backward as the spurt started, a slight push forward as it came to an end.

But why was the spurt not more energetic? Why was he not yanked backward and forward in a sickening fashion?

And then he thought of the mass he no longer possessed. With his remaining mass so tiny, his inertia was similarly tiny. The viscosity of the normal fluid of the bloodstream exerted an enormous cushioning effect, so that the spurts were all but lost in the Brownian motion.

And, ever so slightly, Morrison felt himself relax. He felt something inside himself untighten a bit. The miniaturized environment was unexpectedly benign.

He looked through the ship's transparent hull again, his eyes focusing on the volume between himself and the arterial wall. He could see bubbles, faintly outlined. No, not bubbles, but things of substance - many of them. Some turned slowly and changed apparent shape as they did so, so they were not spheres. They were disks, he now realized.

The truth burst in on him and shamed him. Why was he so slow in identifying them, since he knew he was in a bloodstream? - But then he knew the answer to that, too. He could not really conceive of himself as being in a bloodstream; it was too easy to suppose he was in a submarine making its way through an ocean. He would naturally expect to see the familiar sights of an ocean and would be foolishly puzzled at anything he saw that did not fit his assumption.

He would see the red corpuscles of the blood - the erythrocytes - and fail to recognize them.

Of course, they weren't red but faintly yellowish. Each one absorbed some shortwave light to produce that color. Get them in bulk, though, millions and billions of them, and they would absorb enough such light to appear red - in arterial blood, anyway, and they were in an artery now. Once the cells withdrew the oxygen carried by the red corpuscles, the individual corpuscle would seem faintly bluish, and, in bulk, blue-purple.

He watched the erythrocytes with interest and saw them quite clearly now that he had recognized them for what they were.

They were biconcave discs, the centers depressed on each side. To Morrison, they were enormous, considering that, under normal conditions, they were microscopic, perhaps seven and a half micrometers in diameter and a little over two micrometers thick. Now here they were, swollen objects the size of his hand.