Abstract
Exencephalia has been reported in irradiated CFI mice but there are no reports of its occurrence in untreated mice of this strain. In the course of establishing disease-free breeding colonies from CFI female mice delivered of their offspring by cesarean section, exencephalia was seen frequently. During a 2-week period, 90 litters were delivered; 11 contained exencephalic fetuses, at the rate of one per litter (11 of 90 litters, 12.2 percent; 11 of 1056 fetuses, 1.04 percent). The prevalence of this anomaly in untreated mice of this strain could contribute to overestimates of the effectiveness of low doses of radiation.
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