518 DOROTHEA STARBUCK MILLER 



Research Hospital, we were able to irradiate young mice before testing them 

 for seizure susceptibility. Fi and backcross litters were exposed to a small 

 Go''" source which delivered 350 mrad per day. Since it was not advisable to 

 expose the mothers, and since the litters are tested at 30 days of age, the 

 exposure was limited to from 5 to 7 days after weaning. The total dosage was 

 1.5-2 rad during the ages of 23-30 days. Parallel control litters were weaned 

 on the same day. 



Incidence of Seizures in Fi Generation of DBA/1 by C57BL6 



Table III shows the frequencies of total and fatal seizures in the Fi gen- 

 eration. There were no significant sex difTerences. The first two groups, 

 derived from our original stocks, show the enormous increase in susceptibility 

 which occurred in Room R. The 1956-57 population was derived from new 

 stocks of mice. This DBA/1 pure line exhibited a seizure incidence 10% 

 higher than our original DBA/1. While the higher susceptibility of the 

 DBA/1 parents is reflected in the incidence of their Fj progeny, the seizure 

 incidence in the F, generation icared in Room G declined toward the 



TABLE III 



Incidence of Audiogenic Seizi'res in Fi Generation (DBA/1 X C57BL6) 

 UNDER Different Environmental Radiation Levels 



First trial Four trial 



seizures (%) seizures (%) 



