174 



ORVILLE T. BAILEY 



Fig. 4. Marked vascular Irsions after intracerebral implantation of Ta""". Weil's 

 method X30. Dosage 553 r in 13 days; sacrifice 16 days after completion of radiation. 

 No neurologic deficit. Lesion measured 8 mm in diameter. 



tion. Resistance to such injury incieases in older animals. There is less gen- 

 eral agreement as to whether the adult neurons are directly injured or 

 whether the nerve degeneration is secondary to vascular lesions. 



In the acute phase of the radiation reaction to gamma and roentgen rays. 

 the changes visible by light microscopy in the nerve cells are not striking. 

 Alvord and Brace ( 1957) found that there is pyknosis of granule cells in the 

 cerebellum, which is probably reversible and coincides with a period of 

 clinical neiuologic dysfimction. This is maximal at 8 hoius after 7,500 r of 

 whole body radiation. Similar changes are produced if only the hindbrain 

 and cerebellar regions are radiated, but no alterations occur when this area 

 is shielded. The same type of pyknosis in the cerebellar granule cells has been 

 produced by Vogel et al. ( 1958) using cobalt''" ( 10,000 r), and they also feel 

 that this effect is transient and reversible. The results of Hicks it al. ( 1956) 

 are in agreement. In none ot these studies is there evidence of vascular 



