PATHOLOGIC CHANGES IN BRAIN CAUSED BY ALPHA PARTICLES 389 



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Fig. 3. Alpha particle radiation. S.UOO rad surtace dose; sacrifice at 64 days. A. 

 Cerebellum, showing a zone of shrunken granule cells marked oflT by a sharp lower 

 border. Rarefaction of the granular layer is greatest in the region of ma.ximal depth of 

 the damage. To the left, Purkinje cells in the region of most intense irradiation have 

 disappeared. Glia in the molecular layer ha\e imdergone slight proliferation. B. Cere- 

 brum. The nerve-cell-poor band of damage is marked off by a sharp lower border. 

 .\bo\e the band, scattered nerve cells ha\e disappeared. Both X 65. Van Gieson- 

 hematoxvlin stain. 



the 1,500 rad radiation level (surface dose), the band of damage, present 

 only in the cerebrum, was significantly narrower at 216 days ( Fig. 4 i than at 

 64 days after exposme to 3,000 rad. 



One cerebellum was studied with a view to determining whether the 

 width of the zone of damage was consistent with the stopping power of the 

 particles as expressed bv the Bragg cin\e. The ceiebellum had been exposed 

 to a surface dose of 12,000 rad, and the animal was sacrificed at 24 hours. 

 The lower border of the granule cell pyknosis (Fig. 5) was 720 deep to the 

 cerebellar surface. The pyknotic granule cells were counted in 8 diflferent 

 tissue depths within a 9 X 9.8 cm area on a photograph enlarged 225 times; 

 the number of pyknotic cells for each of the 8 units within the area, when 



