This book retains the basic organization and presentation which were responsible for the success of the previous editions. Preface, The Beginnings of Microbiology, The Methods of Microbiology, The Nature of Microbial World, The Protists, The Procaryotes: An Introductory Survey, Microbial Metabolism: The Generation of ATP, Microbial Metabolism: Biosynthesis, Regulation, Microbial Growth, The Effect of Environment on Microbial Growth, The Relations Between Structure and Function in Procaryotic Cells, The Viruses, Mutation and Gene-Function at the Molecular Level, The Expression of Mutation in Viruses and Cells and Cell Populations, Genetic Recombination, The Classification of Bacteria, The Protosynthetic Procaryotes, Gram-Negative Bacteria: The Chemoautotrophs and Methylotrophs, Gram-Negative Bacteria: Aerobic Chemoheterotrophs, The Enteric Group and Related Organisms, Gram-Negative Bacteria: Myxobacteria and Other Gliding Organisms, Gram-Positive Bacteria: Unicellular Endosporeformers, Gram-Positive Bacteria: The Actinomycete Line, Nonspore-Forming Strict Anaerobes, Microorganisms as Geochemical Agents.