Drawn to the Micronesian island of Pingelap by reports of a community of people born totally colorblind, Dr. Sacks set up a clinic in a one-room dispensary. There he listened to patients describe their colorless world in terms rich with pattern and tone, luminance and shadow. Then, in Guam, he investigated a puzzling neurodegenerative paralysis, making housecalls amid crowing cockerels, cycad jungles, and the remains of a colonial culture. The experience affords Sacks an opportunity to elaborate on such personal passions as botany and history and to explore the meaning of islands, the dissemination of species, the birth of disease, and the nature of deep geologic time.