The Normal Microbial Flora

CONTROVERSY has surrounded the role of the normal microbial flora in health since the early days of microbiology. Pasteur, for one, hypothesized that the normal flora was essential to life.1 Some years later, his hypothesis was tested and convincingly refuted by Reyniers and others at the Lobund Laboratory, University of Notre Dame, who demonstrated that the germ-free state could be maintained for successive generations in various laboratory animals.2 Metchnikoff, in one of many differences with Pasteur, argued that indigenous microorganisms were antagonists that competed with the host for factors essential to life.3 Metchnikoff's proposal has not been so easily rejected. . . .