32 



BRIZZEE, JACOBS, KHARETCHKO AND SHARP 



10 

 AGE (DAYS) 



20 



Fig. 4. Decrease in nucleocytoplasinic ratio between 1st and 20th postnatal days. 



values for neuron soma volume (nucleus + parikaryon ) in the 100 and 200 

 r series are lower than in the controls in the first three developmental stages 

 and increase to values above the control level on the 20th day. The group 

 receiving the highest dose of irradiation (300 r) diverged more markedly 

 from control values than the animals given lower doses, but the diflferences 

 are within the range of error of the methods employed and are not statisti- 

 cally significant. The nucleocytoplasmic ratio (Fig. 4), reflecting the chang- 

 ing relationships between nuclear and cytoplasmic (perikaryon) volume 

 through the four stages of development, was seen to decrease steadily in all 

 groups with no significant differences appearing among irradiated or control 

 groups. 



In contrast to the above findings, marked differences were observed in 

 cortical thickness in area 2 (Fig. 5. Table I) between the controls and 

 animals irradiated at 200 and 300 r {p < .01), and between the 200 and 

 300 r groups themselves {p<.0\). No significant differences were noted 

 between the 100 r groups and nonirradiated rats. 



