This book contains 29 short essays by physician-scientist Lewis Thomas, originally published in the early 1970s in The New England Journal of Medicine. The essays center on science, and range in focus from the molecular (e.g., DNA) to the subcellular to the organism to social interactions and all the way up to the search for extra-terrestrial life. Some themes reappear in several essays: science as a grand, engaging enterprise worthy of the brightest minds; communication between organisms creating the intricate dance of the social organism; the relationship of man to both nature and the grand scheme of the universe.

Lewis is fascinated by communication not only at the cellular level, but also at the pheremonal and cerebral level: "Language, once it comes alive, behaves like an active, motile organism" (90). The ant and its colony, as an example of a simultaneous individual and integrated social organism, form a link for Thomas between the enclosed unit of a cell and the complex interactions of a society. Indeed, macro-micro comparisons continue throughout the essays, and even conclude the final essay, "The World's Biggest Membrane," which lauds the atmosphere as protector, filter, and provider: "Taken all in all, the sky is a miraculous achievement. It works, and for what it is designed to accomplish it is as infallible as anything in nature. . . it is far and away the grandest product of collaboration in all of nature" (48).