GERMFREE LIFE

biological condition characterized by the complete absence of living microorganisms. Gnotobiology comprises the study of germfree plants and animals, as well as living things in which specific microorganisms, added by experimental methods, are known to be present. When one or more known species of microorganisms are added experimentally to a germfree plant or animal, the host, of course, is no longer germfree; both the host and the introduced species are gnotobiotic, however, since all added species are known to the investigator. Precise comparisons between germfree and conventional animals cannot be made unless both are isolated from the environment and fed the same sterile diet. Gnotobiotic research seeks to explore the effects of microorganisms in physiological diseases, to identify the specific causative agents in infectious diseases, and to explore the role of bacteria in protozoan and viral infections. Germfree research currently is directed toward studying the reactions of germfree animals after they have been inoculated with specific known microorganisms. The first attempts to grow germfree animals were undertaken in 1895, with guinea pigs at the Hygiene Institute of Berlin; experiments were continued with chicks for more than a decade with no success. The first successful germfree vertebrate experiments (with chicks) were begun about 1912. Shortly thereafter, germfree goats were kept alive for two months. Subsequent advances in methodology during the 1920s and '30s led to the routine raising of germfree animals.