The glass broke, but only a few in the immediate vicinity heard it in the din. To those who stared at him, he presented a view of his back or the profile of his hat. They glanced at him indifferently, then looked away. Outside the orifice, where the tube had been in the outer of two walls, was an actual port. He gazed through it contentedly. A finger tapped him. "Yes?" he said in a loud voice. The man behind him leaned over. "I've been riding in this plane once a week for five years. I mean, would you mind if I looked out? I've never seen where I'm going." "Glad to have you." The man sat beside him and peered wistfully out. Below were lights, the patterns of cities, roads and towns and in the distance the glare of furnaces. There was also a current of cold air seeping from the space between the double walls. The man looked, shivered, turned up his collar and finally went back to his seat. It was cold, but Merrol remained where he was. There was some satisfaction in asserting himself, but the satisfaction wore off and the cold didn't. His attention was caught by the program which was flickering across the aisle. Doctor Crander--Merrol frowned. Did the hospital want him too? He listened intently. No, they didn't want him. * * * * * Crander sounded tired. "This is an emergency appeal and we'll need a wide response. We have in our care a person with a serious illness we can't diagnose. With so much interplanetary travel we can't determine what causes the disease. It may be an organism from a moon of Saturn or almost anything else. "Our staff is working at top speed. We feel, if we can keep her alive for one week, she'll be out of danger. That is by no means a certainty, but a reasonably accurate forecast. "We have a new theory, largely untested, but we hope it will work. Each person differs from the next and though, when we match limbs and organs, we try to take this into account, we never quite succeed in effecting a perfect biological match. As a result, the character of the blood changes, slightly but significantly. It's as if we had lumped together the various natural immunities of the component bodies and created an entirely new super-immunity." Crander paused. "We need persons who have had five or more major replacements. By major, I mean hands, arms, legs or parts of them--nothing so trivial as ears, or a few feet of skin, or three or four fingers. "It must be at least five, though more are correspondingly better. Nothing less--and please don't apply with only a minor replacement. Two donors have volunteered so far and we have fractioned and administered the blood of one with dramatic, if temporary, results. In a few hours, we'll have to use the second. After that, I don't know what we'll do." Merrol stirred. He was deeply suspicious. "Here's the woman," said Crander. "She needs your help."