it's different for us. We slog on and on for seventy or eighty or maybe a hundred years and eventually it all just becomes too much, and so we sit down and then we lie down and finally we close our eyes and don't open them again, and right at the end we know that it is the end and we simply don't mind. Or don't care: I'm not sure that's the same thing, really, but perhaps it is. -Don't look at me that way, Andrew."
"Dying is a natural thing for humans," Andrew said. "I do understand that, Paul."
"No. You don't. You really don't. It just isn't possible for you to understand. You secretly think that death is some sort of lamentable design flaw in us and you can't understand why it hasn't been fixed, because it ought to be pretty simple to keep on replacing our parts indefinitely as they wear out and break down, the way yours have always been replaced. You've even had an entire body replaced."
"But surely it would be theoretically possible for you to be transferred into-"
"No. It isn't. Not even in theory. We don't have positronic brains and ours aren't transferable, so we can't simply ask someone to scoop us out of a body that we're finished with and put us into a nice shiny new one. You can't comprehend the fact that humans inevitably have to reach a point where they're incapable of being repaired any more. But that's all right. Why should anyone expect you to be able to conceive the inconceivable? I'm going to die soon and that's all there is to it. And I want to reassure you at least in one respect, Andrew: you'll be well provided for financially when I go."
"But I am already quite well provi-"
"Yes. I know that. All the same, things can change very quickly, sometimes. We think we live in a very secure world, but other civilizations have felt just as smug and they had reason sooner or later to see that they were wrong. Anyway, Andrew: I'm the last of the Charneys. I have no heirs except you. There are collateral relatives descended from my great-aunt, but they don't count. I don't know them and I don't care about them. I care about you. The money I control personally will be left in trust in your name and you'll continue to be economically secure as far into the future as anyone can foresee."
"This is unnecessary, Paul," Andrew said, with difficulty. He had to admit to himself that what Paul had said about his not understanding death, not being able to understand it, was true. In all this time he had not really managed to get used to the deaths of the Charneys.
Paul said, "Let's not argue, all right? I can't take the money with me and there isn't anything I'd rather do with it than leave it to you, so that's the way it's going to be. And I don't want to consume any more of my remaining life-span discussing the matter with you. Let's talk about something else. -What are you working on these days?"
"Biology, still."
"What aspect in particular?"
"Metabolism."
"Robot metabolism, you mean? There isn't any such thing, is there? Or is there? Do you mean android metabolism? Human metabolism?"
"All three," Andrew said. " A synthesis of sorts." He paused, and then he went plunging ahead. Why hold anything back from Paul? "I've been designing a system that would allow androids-I mean myself; I am still the only functioning android, am I not?-to draw energy from the combustion of hydrocarbons rather than from atomic cells."
Paul gave him a long, slow look.
"You mean," he said finally, "that you want to make it possible for an android to be able to breathe and eat the same way humans do?"
"Yes."
"You've never mentioned any such project as this to me before, Andrew. Is it something new?"
"Not really. In truth, Paul, it is the reason I began all this biological research in the first place."
Paul nodded abstractedly. It was as though he was listening from a very great distance. He seemed to be having a difficult time absorbing what Andrew was telling him.
"And have you achieved anything significant so far?" he asked, after a time.
"I am approaching something significant," Andrew said. "It needs more work but I think I have succeeded in designing a compact combustion chamber that will be adequate for catalyzed controlled breakdown."
"But why, Andrew? What's the point of it? You know that it can't possibly