"I suppose she explained with a smile and gestures just how much of a strain it is, simply keeping the city going?" "Of course," said Evelyn calmly. "The city's fighting against the jungle, which grows worse all the time. They used to grow their foodstuffs in the open fields. Then within the city. Now they use empty towers and artificial light. I don't know why." * * * * * Tommy grunted again. "This planet's just had, or is having, a change of geologic period," he explained, frowning. "The plants people need to live on aren't adapted to the new climate and new plants fit for food are scarce. They have to grow food under shelter, now, and their machines take an abnormal amount of supervision--I don't know why. The air-conditions for the food plants; the machines that fight back the jungle creepers which thrive in the new climate and try to crawl into the city to smother it; the power machines; the clothing machines--a million machines have to be kept going to keep back the jungle and fight off starvation and just hold on doggedly to the bare fact of civilization. And they're short-handed. The law of diminishing returns seems to operate. They're trying to maintain a civilization higher than their environment will support. They work until they're ready to drop, just to stay in the same place. And the monotony and the strain makes some of them take to _cuyal_ for relief." He surveyed the city from the oval window, frowning in thought. "It's a drug which grows wild," he added slowly. "It peps them up. It makes the monotony and the weariness bearable. And then, suddenly, they break. They hate the machines and the city and everything they ever knew or did. It's a sort of delayed-action psychosis which goes off with a bang. Some of them go amuck in the city, using their belt-weapons until they're killed. More of them bolt for the jungle. The city loses better than one per cent of its population a year to the jungle. And then they're Ragged Men, half mad at all times and wholly mad as far as the city and its machines are concerned." Evelyn linked her arm in his. "Somehow," she told him, smiling, "I think one Thomas Reames is working out ways and means to help a city named Yugna." "Not yet," said Tommy grimly. "We have to think of Earth. Not everybody in the Council approved of us. Aten told me one chap argued that we ought to be shoved out into the jungle again as compatriots of Jacaro. And the machines were especially short-handed to-day because of a diversion of labor to get ready something monstrous and really deadly to send down the Tube to Earth. We've got to find out what that is, and stop it." * * * * *