This is a journey into the submicroscopic world of molecular machines. Readers are first introduced to the types of molecules built by cells: proteins, nucleic acids, lipids, and polysaccharides. Then, in a series of illustrations, the reader is guided through the interior world of cells, exploring the ways in which molecules work in concert to perform the processes of living. Finally, the author shows how vitamins, viruses, poisons, and drugs each have their effects on the molecules in the body.