"Children in Three City," growled Hunt, "are taught the same as in Two City. Men came to this planet to work the mines. There was a company which sent them, and every so often it sent ships to take what the mines yielded, and to bring things the people wanted. Men lived well and happily. The company hung the ribbon in the sky so the hotlands could grow food for the men. But presently the mines could not deliver what they made to the ships when they came. The hotlands grew bigger, the glaciers flowed faster, and the pipes between the cities were broken and could not be kept repaired. So the company said that since the mine-products could no longer be had, it could not send the ships. Those who wanted to move to other worlds would be carried there. Some men went, with their wives and children. But the grandfathers of our fathers' grandfathers were contented here. They had homes and heat and food. They would not go." Hunt regarded the pinkish brook trout fillet he'd just separated. He bit off a mouthful and chewed, thoughtfully. "That really tastes better cooked," said Calhoun mildly. "But it is good this way also," said Hunt. He was grizzled and stocky and somehow possessed of dignity which was not to be lost merely by eating raw fish. He waved the remainder of the fillet. "Then the ships ceased to come. Then sickness came. One City had a sickness it gave to people of Two and Three when they visited it. Two City had a sickness it gave to One and Three. Three City--" He grunted. "Our children in Two say only Two City people have no sickness. Three City children are taught that only Three City is clean of sickness." Calhoun said nothing. Murgatroyd tried to gnaw open one of the nuts he'd brought down from the tree. Calhoun took it and another and struck them together. Both cracked. He gave them to Murgatroyd, who ate them with great satisfaction. Hunt looked up suddenly. "Pat did not give a Three City sickness to Nym," he observed, "so our thinking was wrong. And Nym has not given a Two City sickness to him. His thinking was wrong." Calhoun said meditatively: "It's tricky. But sickness can be kept by a carrier, just as you people have believed of other cities. A carrier has a sickness but does not know it. People around the carrier have the sickness on their bodies or their clothing from the carrier. They distribute it. Soon everybody in the city where there is a carrier--" Calhoun had a moment's qualm because he used the word "city." But to Hunt the idea conveyed was a bare few hundred people. "Soon everybody is used to the sickness. They are immune. They cannot know it. But somebody from another city can come, and they are not used to the sickness, and they become ill and die." Hunt considered shrewdly. "Because the sickness is on clothing? From the carrier?" Calhoun nodded.