Except the asteroids were red cells, bouncy purplish bags moving in a clear, slightly yellowish liquid. An occasional much larger white cell shot forward, filled the screen for a moment, then was gone. What I was seeing looked more like a video game than a medical image.

"Julia," I said, "this is pretty amazing."

Beside me, Julia snuggled closer and smiled. "I thought you might be impressed." Onscreen, Julia was saying, "We've entered a vein, so the red cells are not oxygenated. Right now our camera is moving toward the heart. You'll see the vessels enlarging as we move up the venous system… Yes, now we are approaching the heart… You can see the pulsations in the bloodstream that result from the ventricular contractions…" It was true, I could see the camera pause, then move forward, then pause. She had an audio feed of the beating heart. On the table, the subject lay motionless, with the flat antenna just over his body.

"We're coming to the right atrium, and we should see the mitral valve. We activate the flagella to slow the camera. There the valve is now. We are in the heart." I saw the red flaps, like a mouth opening and closing, and then the camera shot through, into the ventricle, and out again. "Now we are going to the lungs, where you will see what no one has ever witnessed before. The oxygenation of the cells."

As I watched, the blood vessel narrowed swiftly, and then the cells plumped up, and popped brilliantly red, one after another. It was extremely quick; in less than a second, they were all red. "The red cells have now been oxygenated," Julia said, "and we are on our way back to the heart."

I turned to Julia in the bed. "This is really fantastic stuff," I said.

But her eyes were closed, and she was breathing gently.