Konev then said, "Besides, Albert, there is something else we can try. We are approaching a synapse. This axon will end eventually and split up into many fibers, each of which will approach but not join with the dendrite of a neighboring neuron."

"I know that," said Morrison impatiently.

"The nerve impulse, including the skeptic waves, will have to jump the tiny gap of the synapse and, in doing so, the dominant thoughts will be less attenuated than the others. In short, if we jump the synapse, too, we will reach a region where we may, for a while at least, detect what we want to hear with less interference from trivial noise."

"Really?" asked Morrison archly. "This notion of differential attenuation is new to me."

"It's the result of painstaking Soviet work in the area."

"Ah!"

Konev fired up at once, "What do you mean, 'Ah!'? Is that a dismissal of the value of the work?"

"No no."

"Of course it is. If it's Soviet work, it means nothing."

"I just mean that I haven't read or heard anything about it," Morrison said in defense."

"The work was done by Madame Nastiaspenskaya. I presume you've heard of her."

"Yes, I have."

"But you don't read her papers, is that it?"

"Yuri, I can't keep up with the English-language literature, let alone with -"

"Well, when this is over, I'll see that you get a collection of her papers and you may educate yourself."

"Thank you, but may I say that on the face of it I think the finding is an unlikely one. If some types of mental activity survive a synapse better than others, then, considering that there are many hundreds of billions of synapses in the brain, all constantly in use, the final result would be that only a tiny proportion of thoughts would survive at all."

"It's not as simple as that," said Konev. "The trivial thoughts are not wiped out. They continue at a lower level of intensity and don't decline indefinitely. It's just that, in the immediate neighborhood of a synapse, the important thoughts are, for a time, relatively strengthened."

"Is there evidence for this? Or is it only a suggestion?"

"There's evidence of a subtle nature. Eventually, with miniaturization experiments, that evidence will be hardened, I'm sure. There are some people among whom this synapse effect is much stronger than average. Why else can creative individuals concentrate so hard and so long, if they are not less distracted by trivia? And why, on the contrary, are brilliant scholars traditionally absentminded?"

"Very well. If we find something, I won't quarrel with the rationale."

Dezhnev said, "But what happens when we come to the end of the axon? The stream of fluid we're riding will just make a U-turn at that point and carry us back again against the opposite wall of the axon. Do I force my way through the membrane?"

"No," said Konev. "Of course not. We'd damage the cell. We'll have to take on the electric charge pattern of acetylcholine. That carries the nerve impulse pattern across the synapse."

Boranova said, "Sophia, you can give the ship an acetylcholine pattern, can't you?"

"I can," said Kaliinin, "but aren't the acetylcholine molecules active on the outside of the cell?"

"Nevertheless, the cell may have a mechanism for ejecting them. We'll try."

And the trip along the seemingly endless axon continued.

Suddenly the end of the axon was in sight. There was no hint, no warning. Konev noticed it first. He was watching and he knew what he was watching for, but Morrison gave him full credit. He himself was watching, too, and knew what he was watching for, and yet did not see it when it came.

To be sure, Konev was in the front seat, while Morrison had to stare past Konev's head. That was not much of an excuse either.

In the curiously ineffective light of the ship's beacon, it was clear that there was a hollow ahead and yet the current was beginning to veer away from it.

The axon was beginning to break off into branches, into dendrites like those at the other end of the neuron, at the end where the nucleated cell body was. The axonian dendrites at the far end of the cell were fewer and thinner, but they were there. Undoubtedly, a portion of the cellular stream flowed into it, but the ship was in the main stream that curved away and they could take no chances.

They would have to push into the first dendrite encountered - if it could be done.

"There, Arkady, there," cried Konev, pointing, and it was only then that all the rest realized they were reaching the end of the axon. "Use your motors, Arkady, and push over."

Morrison could make out the soft throbbing of the motors as they edged the ship toward the side of the stream. The dendrite toward which they aimed was a tube that was slipping sideways, a huge tube at their size scale, so huge they could only see a small arc of its circumference.

They continued to edge closer to it and Morrison found himself leaning toward the dendrite, as though adding body English could improve matters.

But it was not a matter of reaching the tube itself, merely moving over an eddying section of fluid, a rushing of water molecules that quieted into gentle circles and then slipped beyond into another stream that was curving off in another direction.

The ship made the transition and was suddenly plunging forward into the tube opening.

"Turn off the motors," said Konev excitedly.

"Not yet," grumbled Dezhnev. "We may be too near the countercurrent emerging from this thing. Let me slip over a bit closer to the wall."

He did so, but that did not take long. They were now essentially moving with the current, not against it. And when Dezhnev did finally shut off the engine and pushed back his damp, graying hair, he heaved a great breath and said, "Everything we do consumes a ton of energy. There's a limit, Yuri, there's a limit."

"We'll worry about that later," said Konev impatiently.

"Will we?" said Dezhnev. "My father always said: 'Later is usually too late.' - Natalya, don't leave all this to Yuri. I don't trust his attitude toward our energy supply."

"Calm yourself, Arkady. I will take care to override Yuri if it becomes necessary. - Yuri, the dendrite is not very long, is it?"

"We will come to the ending in short order, Natalya."

"In that case, Sophia, please see to it that we are ready to adopt the acetylcholine pattern at a moment's notice."

"You'll give me the signal, then?" said Kaliinin.

"I will not have to, Sophia. I'm sure that Yuri will whoop like a Cossack when the end is in sight. Shift the pattern to acetylcholine at that moment."

They continued sliding along the final tubular remnant of the neuron they had entered a considerable time before. It seemed to Morrison that, as the dendrite continued to narrow, he could see the wall arc above him, but that was illusion. Common sense told him that even at its narrowest, the tube would appear to be a few kilometers across at their present molecular size.

And, as Boranova had foreseen, Konev lifted his voice in a great cry, probably quite unaware that he was doing so. "The end is ahead. Quick. Acetylcholine before we're swept around and back."

Kaliinin's fingers flickered over the keyboard. There was no indication from inside the ship that anything about it had changed, but somewhere up ahead was an acetylcholine receptor - or, more likely, hundreds of them - and the patterns meshed, positive to negative and negative to positive, so that the attraction between ship and receptor was sharp and great.

They were pulled out of the stream and melted into and through the wall of the dendrite. For a few minutes they continued to be pulled through the intercellular medium between the dendrite of the neuron they had just left and the dendrite of the neighbor neuron.