256 



F. STEPHEN VOGEL 



Fig. 4. Granule tells, as in Fig. 3, 24 hours after exposure to 10,000 r of gamma 

 radiation from a Co"" source. The nuclei are markedly contracted and the nuclear 

 membranes are serrated. The cytoplasmic spaces arc enlarged. The over-all size of 

 these cells is somewhat less than normal; in others, it was greater. Phase Microscopy. 

 X 1200. 



and in stained sections made it clear that these cytologic changes were 

 transitory. The cells in individual clumps survived and became normal in 

 appearance. Cells in nonirradiated cultures did not undergo these cytologic 

 changes. 



Morphologic Effects of Radiation on Granule Cells as Viewed with 



Electron Microscope 



The fine structure of nonirradiated granule cells of rabbits was indis- 

 tinguishable from that of the cells in dogs, and in each species they were 

 strikingly uniform. The cells possessed a large, spherical nucleus with uni- 

 formly distributed, finely granular, abundant intranuclear granules. The 

 dual nuclear membranes were uninterrupted and lay parallel except for a 

 rare out-folding of the external one. The cytoplasm was regularly scant, but 

 clearly visible about the entire nucleus with expansions at the axon hillock. 



