If you’re getting confused by the way I tell you this you have an idea of the way I felt. If you remember that my memory has done some editing and organizing since all this actually happened, you may have an even better idea. It got to be more than I felt like taking. I suddenly realized that I hadn’t had much sleep for a long, long time. The tank wasn’t a comfortable place for that, but there are times when one doesn’t bother with trifles. I slept.

I got in a good, solid eight hours, according to the clock. When I woke up, it was with the conviction that I couldn’t plan anything until I had figured out how these people managed to live as they did, what would have to be done to me if I agreed to stay and most particularly what I would have to arrange to do myself if, after agreeing to stay and being processed, I chose to leave.

Bert had made it clear that he wasn’t going to tell me, but he had admitted saying a little more than he should have, so there might be a chance of my figuring it out for myself.

My memory is supposed to be good. Just what had he said that might mean anything?

The most striking remark was his denial that he was breathing water. Also, there had been something else in that sentence — what was it? — ‘that analysis misses on two counts.” What could that mean?

Grammatically speaking, the most obvious implication of the first phrase was that the liquid now around us wasn’t water. Was this possible? And if it were, was there any other evidence?

Yes, to both.

Many liquids don’t mix well with water — nonpolar liquids in general. Carbon tetrachloride and all the oils, to name familiar ones. However, if this were such a liquid it must be at least as dense as water and probably denser. Not the general run of oils, therefore. Not carbon tet, either, since it’s highly poisonous. The density had to be high because there was no door or valve between this place and the ocean, and oil would have floated to the surface of the Pacific and been spotted long ago.

On that basis, the interface between water and my hypothetical liquid would probably be at the entrance. Memory supported the idea.

As the tank had reached the level of the pit’s mouth on the way in, the subs had hooked more ballast to it — obviously necessary if the new liquid were denser than water and the tank were just barely heavy enough to sink in the latter. The swimmers, too, had taken on more ballast — those ‘tool kits!” Of course. If they had been tools, why put them on coming in from; the sea bottom? Or if outside were a place for recreation only and tools were only used inside, why not keep them at the place they were used? If there had been room in the tank, I’d have kicked myself for not seeing that sooner — or rather, for not following up the doubts I had had at the time.

All right, first working hypothesis. We’re in a nonpolar, nonpoisonous liquid, somewhat denser than water. I think I see why, but let’s not be too hasty.

So that was the second point on which my analysis had been wrong. The people, as Bert said, weren’t breathing water — because they weren’t in water and because they weren’t breathing. I still had trouble believing it, but the logic went marching on.

The basic idea was clear enough. If people didn’t breathe, they didn’t need gas in their lungs. If they didn’t have gas in their lungs, they wouldn’t be bothered by pressure changes. Well, qualify that. They’d have to fill their middle ears and sinuses with liquid, too. If the liquid had about the same compressibility as water (question: why not use water? Tabled for later consideration) then a change in depth would mean no significant volume change in any part of the body.

A few details needed filling in, though. Granted that it would be convenient to be able to do without breathing, how was it managed?

Well, why does one breathe, anyway? To get oxygen into the blood. Will anything do as a substitute for oxygen? Categorically no. Element number eight is the one and only oxidizing agent the human metabolism is geared to use — and ‘geared” is a rather good word in that connection.

But does the oxygen have to come in gas form? Maybe not. If my schooling hasn’t gone by the board, hemoglobin is only interested in O-two molecules, not oxide or peroxide ions or ozone; but up to the time the stuff is delivered to the hemoglobin some of the others are at least conceivable. The first thought would be some sort of food or drink. Could something be taken into the stomach which would release oxygen molecules? Certainly. There was hydrogen peroxide. The oxygen released didn’t start as diatomic molecules, though it got to that state quickly enough. I couldn’t picture anyone in his right mind drinking a slug of peroxide, for several reasons, but the. principle seemed defendable so far.

Could the oxygen get from the stomach to the bloodstream? Not directly, but it could take the same path as the other foods. Into the small intestine and through the villi. I seemed to remember that there is a lot less absorbing surface here than in the lungs, but under the pressure of this depth that might not be a serious lack.

Working hypothesis two, therefore, is that these folks eat or drink something that gives off oxygen gradually. If, under this pressure, the gas always remained in solution, the body would still be relatively indifferent to pressure change. Though my outside passenger of a few hours back might have been in serious trouble after all if he’d gone all the way to the surface with me.

How about carbon dioxide elimination? No problem. Out through the lungs, as usual, and into immediate solution in the surrounding liquid. Maybe that was why the liquid wasn’t water; they might be using something that took up CO2 better, though under this pressure water certainly should be adequate. Of course, with body fluids under the same pressure, it might be more a matter of complex ion equilibrium than simple solubility; perhaps pH control had been necessary. It certainly was inside the body, and this whole idea seemed to be lessening the differences between inside and out.

All this suggested that if I chose to stay down here, they would presumably start pressurizing me. Sometime during the process I’d be given a meal, or a drink, of the oxygen source. That, as far as I could see, would be it, barring minor mechanical tricks for filling my sinuses and middle ears with liquid.

How about getting back to breathing habits? The pressure would have to come down again. The oxygen source in the stomach — yes, that would present a difficulty. If it were still giving off the stuff, and pressure got down near one atmosphere — hmph. Very close timing, doing the job just as the stomach oxygen ran out? Mechanical assistance such as an artificial lung between the time the inside source gave out and natural breathing was resumed? Either way, it would be difficult for me to manage alone, if the need ever arose.

In any case, I could now do some tentative planning, always realizing my hypothesis might be all wet. I was fond of them, though, and felt that it would be at most a case of having to modify details as more information came in. It was a pleasant sensation while it lasted.

Under the circumstances, then, it seemed best to tell Bert that I was staying and waste as little time as possible getting out of this bubble so I could do something useful. I’d developed my own moral standards — made my private Loyalty Oath to Mankind, if you like — long ago, so there’d be no conscience question if they wanted me to take some sort of local declaration before they’d accept me. Probably they wouldn’t; things like that had been worn too thin to be meaningful back in the days when people thought their chief danger was political difference rather than energy shortage. Lodges and similar private groups still used formal oaths, but even these didn’t carry quite the same implications that they used to.