Karl moved impatiently. "I hope you're not turning psychotic. You have a clean record of continuous production and you've never mixed in politics. You've never expressed what you may really think of our Leader even to me, although we've been friends since we were in Medschool, and I hope you never will. And you're making progress with White Martian. Why, my boy, you're all set! What's treasonable about that?" Someone knocked at the door. Hastily David uncovered the fragrant beaker and waved it about as he called, "Come in!" The watchguard looked in for an instant, wrinkled his nose, and quickly shut the door. Laughing, David covered the beaker, and began walking about with long nervous strides, snapping his fingers as he tried to explain. "I'm in trouble, Karl. I've run into something I don't know how to deal with, and I need help, I need advice, I need cooperation. I've lived alone with this thing for ten long years, hoping month after month that something would turn up so I could evade the issue. But nothing has. And now there's going to be a showdown." Karl touched his arm sympathetically. "My dear boy--" "_That's it!_" shouted David. "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." [Illustration] "Their descendants, you mean. Mice don't live that long."