That was tough sledding. He couldn't follow the mathematics or the chemistry very far. No good popularizations were available. But a newsman got an ability to winnow what he learned. Radek didn't have to take notes, he'd been through a mind-training course; after an hour or so, he sat back and reviewed what he had gotten.
The living organism was a small island of low entropy in a universe tending constantly toward gigantic disorder. It maintained itself through an intricate set of hemostatic mechanisms. The serious disruption of any of these brought the life-processes to a halt. Shock, disease, the bullet in the lungs or the ax in the brain—death.
But hundreds of thousands of autopsies had never given an honest verdict of "death from old age." It was always something else, cancer, heart failure, sickness, stroke ... age was at most a contributing cause, decreasing resistance to injury and power to recover from it.
One by one, the individual causes had been licked. Bacteria and protozoa and viruses were slaughtered in the body. Cancers were selectively poisoned. Cholesterol was dissolved out of the arteries. Surgery patched up damaged organs, and the new regeneration techniques replaced what had been lost ... even nervous tissue. Offhand, there was no more reason to die, unless you met murder or an accident.
But people still grew old. The process wasn't as hideous as it had been. You needn't shuffle in arthritic feebleness. Your mind was clear, your skin wrinkled slowly. Centenarians were not uncommon these days. But very few reached 150. Nobody reached 200. Imperceptibly, the fires burned low ... vitality was diminished, strength faded, hair whitened, eyes dimmed. The body responded less and less well to regenerative treatment. Finally it did not respond at all. You got so weak that some small thing you and your doctor could have laughed at in your youth, took you away.
You still grew old. And because you grew old, you still died.
The unicellular organism did not age. But "age" was a meaningless word in that particular case. A man could be immortal via his germ cells. The micro-organism could too, but it gave the only cell it had. Personal immortality was denied to both man and microbe.
Could sheer mechanical wear and tear be the reason for the decline known as old age? Probably not. The natural regenerative powers of life were better than that. And observations made in free fall, where strain was minimized, indicated that while null-gravity had an alleviating effect, it was no key to living forever.
Something in the chemistry and physics of the cells themselves, then. They did tend to accumulate heavy water—that had been known for a long time. Hard to see how that could kill you ... the percentage increase in a lifetime was so small. It might be a partial answer. You might grow old more slowly if you drank only water made of pure isotopes. But you wouldn't be immortal.
Radek shrugged. He was getting near the end of his trip. Let the Institute people answer his questions.