Robert L. Forward, a plump, cherubic physicist of Hughes Research Laboratories at Malibu, and occasional science fiction writer, was demonstrating the mechanism in his usual bright and articulate manner.

"As you see," he said, "we have here a large spinning ring, or doughnut, of particles compressed by an appropriate magnetic field. The particles are moving at 0.95 times the speed of light under conditions which, if I am correct, a change in parity can be induced in some object that passes through the hole of the doughnut."

"A change in parity?" I said. "You mean left and right will interchange?"

"Something will interchange. I'm not sure what. My own belief is that eventually, something like this will change particles into antiparticles and vice versa. This will be the way to obtain an indefinitely large supply of antimatter which can then be used to power the kind of ships that would make interstellar travel possible."

"Why not try it out?" I said. "Send a beam of protons through the hole."

"I've done that. Nothing happens. The doughnut is not powerful enough. But my mathematics tells me that the more organized the sample of matter, the more likely it is that an interchange, such as left to right, will take place. If I can show that such a change will take place on highly organized matter, I can obtain a grant that will enable me to greatly strengthen this device."

"Do you have something in mind as a test?"

"Absolutely," said Bob. "I have calculated that a human being is just sufficiently highly organized to undergo the transformation, so I'm going to pass through the doughnut hole myself." "You can't do that, Bob," I said in alarm. "You might kill yourself."

"I can't ask anyone else to take the chance. It's my device."

"But even if it succeeds, the apex of your heart will be pointed to the right, your liver will be on the left. Worse, all your amino acids will shift from L to D, and all your sugars from D to L. You will no longer be able to eat and digest."

"Nonsense," said Bob. ''I'll just pass through a second time and then I'll be exactly as I was before."

And without further ado, he climbed a small ladder, balanced himself over the hole, and dropped through. He landed on a rubber mattress, and then crawled out from under the doughnut. "How do you feel? " I asked anxiously.

"Obviously, I'm alive," he said. "Yes, but how do you feel?"

"Perfectly normal," said Bob, seeming rather disappointed. "I feel exactly as I did before I jumped through."

"Well, of course you would, but where is your heart?"

Bob placed his hand on his chest, felt around, then shook his head. "The heartbeat is on the left side, as usual-Wait, let's check my appendicitis scar."

He did, then looked up savagely at me. "Right where it's supposed to be. Nothing happened. There goes all my chance at a grant."

I said hopefully, "Perhaps some other change took place."

"No." Bob's mercurial temperament had descended into gloom. "Nothing has changed. Nothing at all. I'm as sure of that as I'm sure that my name is Robert L. Backward."

IASF 1/87