516 DOROTHEA STARBUCK MILLER 



In September, 1956, the colony was mo\ed to new quarters, Room G, 

 which was free of radiation. The unusual seizure frequency immediately 

 subsided. There was little doubt that Room R was implicated in increasing 

 the susceptibility to audiogenic seizures. Further tests were done to determine 

 whether the radiation level in the room was the causative factor. 



Genetic and Environmental Effects 



DBA/1. The shifts in seizure susceptibility in imtreated DBA/1 mice 

 under the several environmental conditions are summarized in Table II. All 

 the litters were derived from oin- inbred stock, which had been maintained 

 by brother-sister matings since 1948. Originally the seizure incidence was 

 moderate, with males more susceptible than females. Under low level irradia- 

 tion in Room R, the frequency of seiziues and of deaths on the 1st trial rose 

 in both sexes, with a greater increase in females. Within 4 trials, the sex 

 difference was reversed, with females significantly more susceptible than 

 males. The transition group was nonhomogeneous, including litters born in 

 Room R and mo\ecl to Room G before being tested at 30 days of age. In 

 this briet period, the freciuency of seizures on the 1st trial declined toward 



TABLE II 



Incidence of Audiogenic Seizures in Untreated DB.A/1 Mice Reared 

 UNDER Different Environmental Radiation Levels 



