He pushed his chair back from the desk, "Maybe it's not too hard to understand. Take 'fire' for example: Man lived in fear of fire for a good many hundred-thousand years--and rightly so, because he hadn't learned to control it. The principle's the same; First you learn to protect yourself from a thing; then control it; and, eventually, we learn to 'harness' it for a useful purpose." He gestured toward the man's cigarette, "Even so, man still instinctively fears fire--even while he uses it. In the case of tissue-regeneration, where the change took place so rapidly, in just a generation or so, that instinctive fear is even more understandable--although quite as unjustified, I assure you." The doctor stood up, indicating that the session was ending. While his patient scrambled to his feet, hastily putting out his cigarette, the physician came around the desk. He put his hand on the man's shoulder, "Relax, take it easy--nothing to worry about. This is a wonderful age we live in. Barring a really major accident, there's no reason why you shouldn't live at least another seventy-five years. After all, that's a very remarkable viral-complex we have doing your 'repair' work." As they walked to the door, the man shook his head, "Guess you're right, Doc. It's certainly done a good job so far, and I guess you specialists know what you're doing, even if folks don't understand it." At the door he paused and half turned to the doctor, "But say ... something I meant to ask you. This 'stuff' ... er, this vaccine ... where did it come from? Seems to me I heard somewhere that, way back before you fellows got it 'tamed' it was something else--dangerous. There was another name for it. Do you know what I mean?" The doctor's hand tightened on the doorknob. "Yes, I know," he said grimly, "but not many laymen remember. Just keep in mind what I told you. With any of these things, the pattern is protection, then control, then useful application." He turned to face his patient, "Back in the days before we put it to work for us--rebuilding tissue, almost ending aging and disease--the active basis for our vaccine caused a whole group of diseases, in itself." Returning the man's searching gaze, the doctor opened the door, "We've come a long way since then. You see," he said quietly, "in those days they called it 'cancer'." Transcriber's Note: This etext was produced from _Analog_ September 1962. Extensive research did not uncover any evidence that the U.S. copyright on this publication was renewed. Minor spelling and typographical errors have been corrected without note. Original punctuation style has been retained.