Gnotobiology is the study of the effects of specific microorganisms on germ-free plants and animals living in a sterile environment…. Today gnotobiological experiments are providing useful or potentially useful information that may radically change some aspects of world health. Among the questions considered [in Germfree Life: A New Field in Biological Research] are the possibility of immunization against tooth decay, the effects of bacteria on production of some vitamins, and the efficacy of microflora in slowing the process of cancer. The straightforward, brisk writing is lucid, the material neatly organized, the subject one of the most intriguing on the biological frontier.