Part two of a six-part series on pollution. The ways man has succeeded, and failed, to duplicate in his cities the checks and balances of the natural environment. At its best, the city is a marvel of controlled environment, protecting people from the elements and offering them a broad spectrum of choice in style of living. At its worst, the city is noisy, dirty, crowded, hot and monotonous. This program looks at how man must try to make urban life a part of the global cycle of nature, or perish.