Abstract: "Micronuclei of bone marrow polychromatic erythrocytes of 10 germfree guinea pigs and 4 GF-rabbits were compared respectively with that of 10 conventional guinea pigs and 4 CV-rabbits. It was found that the frequencies of micronuclei in germfree animals were rather lower than that in conventional ones. The frequency of micronuclei in GF guinea pigs was 0.68‰, sharp in contrast to that of 7.55‰ in CV guinea pigs, similarly, 0.72‰ in GF rabbits and 5.76‰ in CV rabbits. The differences between them were statistically significant (P<0.001). We have known that germfree animal can alive much longer than conventional animal though the later were raised in most ideal environment. This is accord with that the genetic material of germfree animal is more steadiness than that of conventional one. In this consequence, we suggested that under the same conditions of genetic backgrounds, physical and chemical factors, the effect may be induced by microorganism-biofactors. But how these biofactors act on bone marrow PCE cells, and how strong is the. intensity of the effect on bone marrow PCE cells? All those still needs further study."

Key words: "Micronuclei frequencies, Germfree Guinea pigs, Germfree Rabbits, Bone Marrow Polychromatic erythrocytes "