"What's what?"

"That's what I'm trying to tell you. Why do you always call me your 'dear boy?' You know I'm a year older than you are."

"It's just habit, I suppose. You _look_ so young--your hair is black, while mine is nearly white. You're full of vigor, while I begin to creak with middle age. I didn't realize that I irritated you with my little phrase. I should think you'd be pleased that you have somehow managed to sip at the fountain of youth."

David sank down on a stool. "I'm not pleased. I'm terrified."

"What do you mean?"

"I mean that's exactly what's happened. I have sipped at the fountain of youth. I've discovered how to keep people from growing old. I myself have not aged a bit in the last ten years."

There was a long silence. Karl sat unmoving, his face like stone.

"I don't believe you," he said at last.

"It's no longer a question of belief. In a few days everybody will know, the proof will stare you in the face. And what will happen then?"

"Evidence?" Karl asked. "I can't accept a statement as a fact."

"Would you like to see my mice? Come with me."

David Wong hurried into the small animal room and paused before a stack of wire cages in which furry creatures darted and squeaked.

"You remember when we were working on Blue Martian, those peculiar mutants we found in our mice, and how I used six of them in trying to make antibodies to the virus?"

"I remember," said Karl. "They were spotted with tufts of white hair on the right forelegs."

David took down a cage, thrust in his hand, and brought out two of the tiny black mice which crawled over his trembling hand. Their right forelegs bore tufts of long white hair.

"These," he said, "are the same mice."

[Ill.u.s.tration]

"Their descendants, you mean. Mice don't live that long."

"_These_ mice do. And they'll go on living. For years I've lived in fear that someone would notice and suspect the truth. Just as for years, every time someone has laughed and told me I never seemed to age a day, I've been terrified that he might guess the truth. I'm _not_ aging."

Karl looked dazed. "Well, my boy, you've got a bear by the tail. How did you find the elixir or whatever it is?"

"You remember the early work with radioactive tracers, a couple of hundred years ago, that proved that all our body cells are in a continuous state of flux? There's a dynamic equilibrium between the disintegration and the resynthesis of the essential factors such as proteins, fats and amino groups, but the cell directs all the incoming material into the right chemical structures, under the influence of some organizing power which resides in the cell.

"Foreign influences like viruses may disrupt this order and cause cancer. The cells are continually in a state of change, but always replace their characteristic molecules, and it is only as they grow older that they gradually become 'worn out.' Then the body grows old, becomes less resistant to infection, and eventually succ.u.mbs to one disease or another. And you know, of course, that viruses also have this self-duplicating ability.

"I reasoned that at birth a man had a definite, finite amount of this essential self-duplicating ent.i.ty--SDE--in his body cells, a kind of directing factor which reproduces itself, but more slowly than do the body cells. In that case, with the normal multiplication of the cells, the amount of SDE per cell would slowly but surely grow smaller with the years. Eventually the time would come when the percentage would be below the critical level--the cells would be less resistant, would function with less efficiency, and the man would 'grow old.'"

Karl nodded soberly. "Reasonable hypothesis."

"But one day, by pure chance, I isolated a component which I recognized as being the factor essential to the normal functioning of body cells.

It hit me like a toothache. I found that I could synthesize the SDE in the lab, and the only problem then was to get it into a man's cells. If I could do that, keep the SDE level up to that of youth, a man would stop aging! Since viruses penetrate our cells when they infect us, it was no trick at all to effect a chemical coupling of the SDE to the virus. I used Martian Blue, since it was handy, and its effects are usually brief.

"Presto! Old age is held at bay for another twenty or thirty years--I really don't know how long. These mice were my first experiment, and as you see, they're still alive. Next, I tried it on myself."

David put the mice back in their cage, locked it, and returned to the lab.

"Tomorrow, the whole thing is bound to come out because Tanya Hachovnik is coming back. You know her sister Leah--gray, dried-up, soured on life. Well, I've had ways of checking, and when Tanya Hachovnik walks into the Inst.i.tute, everyone will see her as the same luscious redhead of twenty-five we knew ten years ago. I realize that what I did was a criminal act. I didn't think the thing through or I wouldn't have been such a fool. But when I made those final experiments, I used the Hachovnik twins for a controlled pair."

"You must have been crazy!"

"Perhaps I was. I'd tried it on myself, of course, with no bad effects except a few days' fever, but I realized that without a control I never could be sure the SDE was actually working. It might be just that my particular genetic const.i.tution caused me to age more slowly than the average. So I chose the twins. To Leah I gave the attenuated Martian Blue, but to Tanya I gave the simple Blue coupled with SDE. The experiment worked. Identical twins--one grows old like other people; the other remains young. I know now, Karl, how to prolong youth indefinitely. But what in the name of Leader Marley shall I do with my knowledge?"

Karl Haslam absently twisted his white hair and spoke slowly, as though he found trouble in choosing his words.

"You realize, of course, that it is your duty to acquaint Leader Marley with all the details of your discovery?"

"Is it? Can you imagine what this will do to our society? What about the generations of children coming into a world where no places have been vacated for them by death? What about the struggles for power? Who will decide, and on what basis, whether to confer or to withhold this gift?

There'll be riots, civil wars. I know that I'm only a scientist; all I ever wanted from life was to be left alone, in a peaceful laboratory, and let other people worry about the world and its troubles. But now--don't you see that by the mere fact that I made this discovery, I've lost the right to sit by quietly and let other people make the decisions?"

"But, David, you and I aren't able to handle such a problem! We're only Research!"

"I know. We're inadequate, yet we have the responsibility. The men who created atomic power probably felt inadequate, too, but could they have made as bad a mess of handling it as others did? Suppose I did turn this over to Marley--he'd use it to become the most absolute tyrant in the history of the race."

Karl ran his fingers through his hair and smiled crookedly. "Well, you could always start a revolution, I suppose, and start by a.s.sa.s.sinating the Leader."

"With what kind of weapon? Men like you and me are not allowed to own so much as an old-fashioned pistol. Except for the Military, Marley's the only man allowed to wear a Needler. And, besides, I'm a Research, not a Military. I hate violence and I'm naturally conditioned against killing."

"Then you shouldn't have got into this mess. It would have been far better never to have discovered this SDE. I presume your notes are safely locked up, by the way?"

David grinned. "Don't worry about my notes; they're written in Coptic.

You remember when I was still in Medschool and made my first important discovery, how to prevent the development of hereditary baldness by the injection of certain parahormones? Leader Marley rewarded me with a Free Choice, and I chose to learn a dead language. Not half a dozen men in the world could read my notes."

"If your notes are safe, why don't you just destroy your mice and get rid of your proof that way?"

"And the Hachovnik twins?"

"You could at least keep Tanya out of sight."

"Don't be a fool. That would only be a temporary measure and has nothing to do with the real problem. Lanza and Marley may suspect the truth right now, for all I know; they keep such close watch on my work.

Anyway, the secret is bound to come out sooner or later."

Dr. Haslam clasped his hands and stared at them for a long while. His lined face looked grayer than ever.

He looked up at last with a faint smile. "Well, my boy, I never asked you to discover this stuff, but since you have--I hereby burn my bridges! You're right, we can't give it to Marley. But you can't handle it alone. What we need is time, and we haven't got it. We shall both be liquidated before this is over, there's no doubt of that, but we must do what we can. When is Tanya arriving?"

"Tomorrow night, on the Playground Jet."

"And you see Leader Marley when?"

"Next Wednesday."