330 D. SLAD16-SIMIC, N. ZIVKOV16, D. PAVIC, AND P. N. MARTINOVITCH 



Effects of doses 0/ 100 r 



The total number of germ cells in the ovary of 17-day-old rats; exposed 

 when 8 days old, decreased by 85% and the number of primary oocytes by 

 more than 96% as compared with control ovaries of the same age. On examin- 

 ing the histological sections, many empty nests were found, left by degener- 

 ated primary oocytes. Apparently, most of the primary oocytes were heavily 

 damaged and killed by the dose of 100 r within the first 9 days following 

 exposure. After 9 days, the number of germ cells kept on decreasing at the 

 same rate as before. By the time these rats are 50 days old they may be 

 considered sterile. In all the histological sections of the ovaries, a considerably 

 higher percentage of growing follicles was noticed, ranging from 62 to 81%. 

 The high percentage of growing follicles in the late period after irradiation 

 could only suggest that the primary oocytes are stimulated to grow and 

 develop. 



Effects of doses of 50 r 



In 17-day-old rats, irradiated when 8 days old, a statistically non-signi- 

 ficant decrease in the total number of germ cells was observed, as compared 

 with the controls. The number of the primary oocytes was also reduced, but, 

 in comparison with the controls, the difference in estimated numbers proved 

 to be highly significant. The decrease in the number of primary oocytes was 

 counterbalanced by a significant increase in the number of growing follicles. 

 The number of mitotic divisions in the granulosa cells increased as weU. As a 



