EFFECTS OF HIGH-DOSE RADIATION ON BRAIN 251 



tion of the cerebral blood vessels, leptomeninties, and choroid plexuses. 

 These lesions were not evident in monkeys exposed to 1,000 r. They were 

 present in some animals, but equixocally or in minimal intensities, after 

 exposine to 2,500 r. They were found with increasing frecjuency and in- 

 tensity after doses of 5,000 and 10,000 r. They showed slight increases with 

 £;reater dosages up to 30,000 r. The severity of the lesions differed appreci- 

 ably from animal to animal. e\en when ex]30sure and sur\i\al conditions 

 were essentially identical. 



The cytologic chanoes were well established within 2 hours after radi- 

 ation. They were dynamic, for their intensity increased rapidly within the 

 next 8 to 24 hours and then regressed precipitously, the lesions being min- 

 imal or absent 96 hours after exposine. 



The pathologic alterations were ol the same character and intt'nsity 

 whether the head and body or only the head was irradiated. They did not 

 occm- when the radiation was applied to the body with the head shielded, 

 the findings pro\idecl e\idence that these cytologic responses were induced 

 by the ionizing rays acting directly upon the intracranial tissues, neither 

 being initiated nor enhanced by exposure of other regions of the body. 



Granule Cp:ll Change 



The morphologic appearance ot the affected cells was notably sin:iilar in 

 monkeys and rabbits, being regularly characterized by a reduction in the 

 diameter of the nucleus to as much as one-half the normal, with marked 

 condensation of the intranuclear chromatic material. Narrow margins of 

 basophilic cytoplasm were visible about some of the contracted nuclei, and 

 these often stained deeply with pyronin. Up to 50''r of the granule cells of 

 a single animal were severely altered: most others remained normal: few 

 showed intermediate degrees of change. Usually the affected cells were 

 haphazardly distributed throughout all portions of the internal granular 

 layer and cerebellum. In some animals, there was preferential localization, 

 the vermis and deeper portions of the granular layer being most often so 

 inxolved. Golgi and Purkinje cells were regularly spared. The pyknotic cells 

 were more widely separated from one another than nonpyknotic ones. The 

 appearance resembled that caused by extracellular edema, although regu- 

 larly unaccompanied by coagulated fluid. The widened intercellular spaces 

 were infiltrated by only a few leucocytes and macrophages and rarely con- 

 tained hemorrhages. Neuronophagia was absent. Perivascular cuffing by 

 leukocytes was minimal in the cerebellar cortex, particularly so in the 

 granular layer. 



The initial cytologic changes in the granule cells of dogs was also charac- 

 terized by contraction of the nucleus, but this was accompanied by nuclear 



