As Silent Springs, which borrows its title from the work of biologist and conservationist Rachel Carson, highlights the deleterious effects of pesticides, it indicates how these amphibians, among the oldest forms of life on earth, are threatened by change that comes too quickly. All that may remain, the film seems to suggest, are dusty slides seen in early scenes through an antique microscope. Like the series of stony faces spouting water, their neatly labeled procession freezes an image of rarefied life.