"That's no argument, Natalya," said Morrison impatiently. "Why don't we simply do deliberately what a real glucose molecule would do by chance? Especially now, when we're part way through the joint. Why are we stuck in position?"

Konev said, "I'm on Albert's side. Diffusion probably isn't a passive leakage. There's some sort of interaction between the diffusing object and the barrier through which the diffusion takes place - except that no one knows what the interaction might be exactly. Especially here, where we face the blood-brain barrier."

"We're here at the barrier," said Dezhnev. "You're the brain expert. Can you look around and tell us how this diffusion works?"

"No, I can't. But glucose is one molecule that gets through the blood-brain barrier easily. It must because it is the brain's sole fuel for energy. The trouble is that while the ship is as small as a glucose molecule, it isn't a glucose molecule."

"Are you getting at something, Yuri," said Boranova, "or is this a lecture?"

"I'm getting at something. We had the ship become uncharged in order to lunge into the joint, but why leave it uncharged now? Can it be given the charge pattern of a glucose molecule? If so, it will be a glucose molecule as far as Shapirov's body is concerned. I suggest you order it done, Natalya."

Kaliinin did not wait for the order. She said, "It is done, Natalya."

(They each addressed Boranova, Morrison noted. Each still maintained the fiction of the other's nonexistence.)

Dezhnev said, "And the joint's pressure decreases at once. It recognizes a friend, so it bows politely and steps aside. My father's mother, long may I keep her memory, would have cried out, 'Black magic,' and at once would have hidden beneath the bed."

"Arkady," said Boranova, "increase the power of the engines and pass through before the joint notices that underneath the glucose pattern is something that is not glucose."

"Yes, Natalya," said Dezhnev.

Morrison said, "This one is yours, Yuri. Your suggestion was just right. In hindsight I see that I should have thought of that, too, but the fact is, I didn't."

Konev said gruffly, as though finding praise something he couldn't handle, "It was nothing. Since the brain lives on glucose, we got down to glucose size. Eventually, we would have had to have a glucose pattern, and as soon as you asked the question why we weren't diffusing when we should have been, I realized we needed the pattern already."

Dezhnev said, "Members of the expedition, we are through the joint. We are out of the bloodstream. We are in the brain."

In the brain, thought Morrison, but not in a brain cell. So far they had only passed from the intercellular space between the cells of the capillary wall, into the intercellular spaces of the brain where the support structures existed that maintained the form and interrelationships of the nerve cells, or neurons. Remove them and the cells would squash into amorphous masses, pulled together by gravity and unable to maintain any sensible function.

It was a jungle, made up of thick viny threads of collagen. (This was the nearly universal animal connective protein that fulfilled the function of cellulose in plants, less cheaply, since it was protein rather than carbohydrate, but far more flexibly.) Through the eye of ultraminiaturization, those collagen threads, totally invisible without an electron microscope, looked like tree trunks, leaning this way and that in a world in which gravity was of little importance.

There were finer and still finer threads. Morrison knew that some of them might be elastin and that the collagen itself might come in subtly different varieties. If he could see the whole in a wider view, from a less-miniaturized standpoint, he would have been able to detect order and structure. At this level, however, it was chaotic. One couldn't even see far in any direction; the overlapping fibers blocked vision.

Morrison became aware that the ship was moving very slowly. The four others were each staring around in wonder. Either they had not expected this (Morrison hadn't, for he had been too interested in the electrical properties of the brain to think much concerning its microanatomy) or, if they had, they had nevertheless failed to visualize it.

Morrison said, "How do you expect to find your way to a neuron? Does anybody know?"

Dezhnev was the first to answer, "The ship can only move straight ahead, so we move straight ahead until we get to a cell."

"How do we move straight ahead through this jungle? If we can't steer the ship, how do we move around obstacles?"

Dezhnev rubbed his chin thoughtfully. "We don't move around, we push around. The ship will move past one of those objects and there will be more friction on the contact side than on the other, so our path bends, like a comet rounding the sun." He smiled. "Cosmonauts do that when they use gravity to skim around a satellite or planet. We'll do it to skim around those things."

Konev said morosely, "Those things are collagen fibers."

Morrison said, "Some of them are pretty thick. You won't always pass by. You'll hit one head-on and stay there and if you can only move forward, what will you do? This ship was designed only for the bloodstream. We're helpless out of it with nothing to carry us along."

Boranova interposed. "Arkady, you have three microfusion engines and the jets, I know, are arranged at the rear at the apices of an equilateral triangle. Can you fire only one of them?"

"No. One contact controls all three."

"Yes, Arkady, that is how it is now. But you designed the ship and you know the details of its controls. Is there anything you can do to modify them so that you can fire them one at a time?"

Dezhnev took a deep breath. "Everyone told me over and over again that I must cut corners, that I must save the budget, that I must do nothing to irritate the bureaucrats."

"Aside from that, Arkady, is there anything you can do?"

"Let me think. It means jury-rigging. It means finding something to make switches out of, and extra wire, and who knows if it will work or how long it will work if it does, and if we won't end up worse than we are. I see what you mean, though. If I can fire only one of the engines, it will set up an unbalanced thrust."

"You'll be able to steer then, depending on which you fire."

"I'll try, Natalya."

Morrison said angrily, "Why didn't you think of this when we were in the wrong capillary? It might have saved me the small trouble of nearly dying trying to turn the ship by hand."

Dezhnev said, "If you hadn't so promptly suggested turning the ship by hand, we might have thought of it - but it wouldn't have been a good idea."

"Why not?"

"We were in the current of the bloodstream. The ship is carefully streamlined to take advantage of it and its surface is designed to allow water to flow past it without turbulence, which makes it all the harder to turn out of the current. It would have taken much longer than turning by hand - and very much more energy. The narrow confines of the capillary must be remembered, too. Here, there is no current and because we've been so miniaturized there is a great deal of room."

"Enough," said Boranova. "Get to work, Arkady."

Dezhnev did so, rummaging through a tool chest, removing a cover plate and studying the control details within, maintaining through it all a kind of incoherent muttering.

Konev, his hands clasped behind his neck, said, without turning, "Albert, tell us about those sensations you receive."

"Sensations?"

"You were telling us about them just before we got the news from the Grotto that we were located in the correct capillary. I'm talking about the sensations you experienced when you were trying to analyze the thought waves."