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Neoplasia Induced in Rat Embryos by Roentgen Irradiation^*

( Department of Anatomy, College of Medicine, University of Cincinnati, Cincinnati, Ohio, and School of Medicins and Dentistry, University of Rochester, Rochester, N.Y.)

Rat embryos exposed to x-radiation on the ninth day of gestation developed discrete tumorlike growths in and around the brain. The incidence of such tumors was directly related to the dosage of x-rays. They first appeared on the second day after irradiation and thereafter exhibited varying capacities for growth and differentiation. Some grew for 1 or 2 days, then disappeared as a result of dispersal of the cells; others grew rapidly until the fifth ar sixth post-irradiation day, then became atrophic; and still others continued to grow slowly until the seventh or eighth day, then became static or underwent atrophic regression. Few remained in newborn animals, and these were small and gave no evidence of proliferative activity. Although the tumor-bearing animals had a somewhat higher mortality than the nonirradiated controls, neither prenatal nor postnatal death could be attributed to the presence of the tumors.

^* Based on work performed under contract with the United States Atomic Energy Commission at the University of Rochester Atomic Energy Project, Rochester, N.Y.

Received 11/26/51.