EFFECTS ON BLOOD-BRAIN BARRIER, CEREBRAL BLOOD \ ESSELS 417 





Fig. 4. This figure demonstrates delayed white matter degeneration (arrows) seen 

 in the internal capsule of a monkey given 1.500 r to the head and sacrificed 8 months 

 after x-irradiation. These regions showed areas of demyelination and neuroglial scar 

 formation. Clajal-gold sublimate impregnation. X 80. 



One is left to wonder whether our methods of determining the effects of 

 lower x-irradiation doses on the aduh brain ha\-e been, to this time, sharp 

 enouoh to detect the more subtle changes which may be taking place. The 

 axiom that the brain is relati\ely resistant to radiation mi^ht be questioned 

 purely on the lack of sensitix e methodolooy. When Rose i 1958) is able to 

 detect vascular permeability changes iitilizino- only several hundred roent- 

 gens, and Ganolofl" and Haley 1960) show that only 200 to 400 r are re- 

 quired to alter spontaneous and exoked electrical actixity in certain parts of 

 the brain, it is time to reconsider our opinions of the radiosensiti\ity of the 



