PATHOLOGIC CHANGES IN BRAIN CAUSED BY ALPHA PARTICLES 397 



in the cerebellum and cerebrum at 3 hours and a zone of damae:e at 4 hours. 

 At these two times many more nerve cells were necrotic at 12.000 than at 

 6,000 rad exposure. 



Glial lulncrability and reactivity 



Van Gieson-hematoxylin preparations were available from material ex- 

 posed to all the dose levels: metallic impregnations, only from the 6,000 rad 

 surface dose. For ob.servations on astrocytes, Cajal's gold chloride method 

 was employed, and for the study of oligodendroglia and microglia, Penfield's 

 modification of Hortega's silver carbonate technique was used. 



In Van Gieson-hematoxylin preparations from brains exposed to the 1 ,500 

 rad surface dose of alpha particles, no glial changes were evident (Fig. 4). 

 At 3,000 rad, enlarged astrocytic nuclei were noted in the damaged zone of 

 the granular layer of the cerebellum at the 20 day period, and, at the same 

 level, occasional Bergmann glia were faded and a few hyperplastic glia were 

 evident in the somewhat disrupted molecular layer. In the zone of damage 

 in the cerebrum, glia had obviously increased in number, and focal collec- 

 tions of polymorphous reacti\e cells were seen here and there. At subse- 

 quent stages glial reaction was more pronounced. 



At the 6,000 rad surface dose of alpha particles and protons, damage to 

 glial cells was noticeable in the cerebellum in Van Gieson-hematoxylin prep- 

 arations around the 4th day. consisting of chromatin loss in the nuclei of 

 Bergmann cells and in cells of the molecular layer in the region correspond- 

 ing to the Bragg peak. Subsequently, in the region of the upper slopes ot the 

 Bragg cui-ve, glia in the molecular layer, and. in less measure, those ot the 

 Bergmann layer, underwent multiplication Figs. lA and 2A). Glia in the 

 region of the Bragg peak sometimes disappeared. Glia had trequently multi- 

 plied in damaged intrafolial white matter as well. In the cerebral C(>rt( x in 

 the region of the anticipated Bragg peak area, damage of isolated satellites 

 and other glia was visible at various stages from 6 hours onward, and at later 

 stages mitosis was evident i Fig. 8E i . 



In Cajal preparations from brains exposed to 6.000 rad surface dose the 

 first changes in astrocytes in the cerebellum and the cerebrimi were noted 

 at the 48 hour stage. Astrocytes in their entirety were enlarged and had an 

 increased affinity for the gold chloride. In the cerebellum these changes 

 were visible in the irradiated region of the cortex and in the intrafolial white 

 matter, and later beneath the band, where Bergmann cells as well as astroglia 

 exhibited prominent hypertrophy (Figs. lOA and lOB). In the cerebral cor- 

 tex in early stages, astroglial reaction was particularly conspicuous in the 

 region adjacent to the interhemispheric fissure. Subsequently, the reaction 

 increased in intensity, and around the 3rd or 4th day a nerve-cell-poor band 



