254 F. STEPHEN VOGEL 



the passage of 72 to 96 hours, the inflammatory cells lysed and the exudate 

 lessened, but with residual perithelial edema and scant numbers of macro- 

 phages and lymphocytes still present at the latter times. 



Meningitis 



Initially the exudate was perivascular and spotty. It persisted as such in 

 some animals, but disseminated over the gyri and spread into the sulci in 

 most. The cellular composition varied with duration after exposure, but 

 also difTered somewhat in animals with identical postirradiation states. 

 Earlier polymorphonuclear leucoctyes predominated in great numbers; later, 

 with decreases in the cellular concentrations, lymphocytes and macrophages 

 were relatively more abimdant. Generally, macrophages persisted and with 

 their contents of cellular debris constituted the inflammatory residue in 

 animals killed 96 hours after exposure. 



Choroid Plexitis 



The choroid plexuses in the lateral, 3rd, and 4th ventricles were equally 

 involved. The intensity and cellular composition of the inflammatory exu- 

 date generally paralleled that in the meninges and in the cerebral blood 

 vessels. Edema of the fibrous tissue stroma usually antedated the exudation 

 of cells into these regions. The choroidal epithelium was generally spared, 

 but ulceration followed on frons with imusually heavy exudates. The epi- 

 thelium was reconstituted, and the inflammation had regressed in most 

 animals by 96 hoius after exposure. 



Morphologic Effects of Gamma Radiation on Granule Cells in 



Tissue Culture 



The cells in explants of cerebellum from new born mice proliferated 

 rapidly and migrated in sheets centrifugally onto the glass. Many of these 

 cells had rounded nuclei with one or several small nucleoli, finely particulate 

 chromatin material, a well defined nuclear membrane, and scant or un- 

 detectable cytoplasm. Slender, short processes radiated from the perikaryon 

 of some. These cells with distinctive cytologic features as .seen with the 

 phase microscope and in sections stained with hematoxylin and eosin were 

 considered granule cells (Fig. 3). Also abundant in cultures 5 to 10 days 

 old were cells with more elongated nuclei, coarse chromatin material, and 

 bipolar or diffusely radiating cytoplasmic strands. These resembled fibro- 

 blasts derived from other tissue sources and were identified as such with 

 phase and light microscopy. Some with similar appearances were viewed as 



