332 D. SLADIC-SIMIC, N. ZIVK0VI(5, D. PAVIC, AND P. N. MARTINOVITCH 



When exposed females were 50 days old we caged them with male rats 

 and their fertility was observed. The results for the fertility of the X-ray 

 treated rats and for their progeny are given in Table IV. 



Table IV 



No ^'* Total ?°-f Micro- and p^^,,^^ 



Dose of "■ parturition ^ . No. of death anophthalmia ^^ ^^^^^^.^^ 



X-rays ^f Litter dwarfs before No. of ^^..^env 



'^^^^ size P'^'S'^y maturity rats P'"^'"^ 



controls 11 7-6 ± 0-3 84 — — — — 



P < 0-02 



50 r 18 9-2 ±0-5 165 13 16 — 9-7 



Fi of rats 



irradiated 37 7-2 ± 0-4 268 18 Uf 3 10-4 



with 50 r 



t Among these 14 animals, 7 were dwarf; 4 animals died immediately after dehvery. Three 

 rats which appeared normal also died. 



The litter size was significantly larger in the exposed rats than in the 

 control animals, which suggests that the stimulation of the oocytes represents 

 a lasting effect to X-ray exposure. According to our knowledge, the process 

 of growth of the oocyte is completed in about 12 days. If this is true for the 

 irradiated oocytes as well, then we have to suppose that the exposure 

 stimulates the primary oocytes to initiate their growth and further develop- 

 ment. This stimulation may be a direct one on the ovaries or indirect via the 

 pituitary gland. This problem could be solved only by local irradiation either 

 of the ovaries or the pituitary gland. Russell and Russell (1956) irradiated 

 adult animals with the sterilizing dose of 400 r and according to them in the 

 exposed mice "... the mean number of fertile eggs per female is significantly 

 increased at short irradiation-to-fertilization intervals and decreased just 

 before sterility sets in ". The litter size in their experiments was smaller in 

 the irradiated females than in the controls due to pre-natal death. In our 

 experiment, after exposure to a much lower dose of X-rays, the litter size 

 was larger in comparison with the controls, but so far we have no records on 

 pre-natal death of embryos. On the other hand, 13 out of 165 descendants 

 were dwarfs. The body weight of the dwarf animals was half the weight of the 

 controls of corresponding age. One of them was sacrificed and the remaining 

 12 died before reaching maturity. In F^, 9-7% of mortality was recorded, 

 whereas there was not a single case of dwarfism or mortality before maturity 

 in the controls. 



