For years, questions lingered about how essential the microbial flora is to normal life and what functions various members of the flora might serves. the need for animal models to further investigate these questions led eventually to development of laboratory strains of Germ-free, or axenic , mammals and birds. The techniques and facilities required for producing and maintaining a germ-free colony are exceptionally rigorous. After the young mammals are taken from the mother aseptically by cesarian section, they immediately transferred to a sterile isolator or incubator. The newborns must be fed by hand through gloved ports in the isolator until they can eat on their own, and all materials entering their chamber must be sterile. Rats, mice, rabbits, guinea pigs, monkeys, dogs, hamsters, and cats are some of the mammals raised in the germ-free state. Experiments with germ-free animals are of two basic varieties: 1. general studies on how the lack of animal microbial flora influences the ...