"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.
"Different carriers have different sicknesses. So one carrier in One City might have one disease, and all the people in One City became used to it while they were babies—became immune. There could be another carrier with another sickness in Two City. A third in Three City. In each city they were used to their own sickness—"