192 NORBERT SCHUMMELFEDER 



In 30 minutes following exposure to 60,000 r, swelling of nuclei and 

 cytoplasm occurred in granule cells, Purkinje cells, and basket cells in deeper 

 parts of the molecular layer. The interstitium of the molecular layer exhib- 

 ited slight vacuolation. 



In 1 hour after 60,000 r, there was greater swelling of the various nerve 

 cells, and the granular layer was loosened. Vacuolation of the molecular 

 layer was increased. The chromatin in the swollen nuclei of the granule 

 cells was condensed in the form of irregularly shaped coarse bodies located 

 on the nuclear membrane. The swollen nerve cells within the molecular 

 layer had a clear space around their nuclei. These spaces contained small, 

 thread-like, ragged or flaky, cytoplasmic residues, often attached to the 

 nuclei (acute cell swelling). The degree of nerve cell swelling was slight in 

 upp)er parts of the molecular layer and increased progressively down to the 

 Purkinje cells. Within the molecular layer, the nuclei of glial cells were 

 slightly swollen or occasionally pyknotic. Vacuolation (status spongiosus) 

 of the molecular layer was evident ; the vacuoles were at first round, then 

 oval, and increased in size downward from the cerebellar surface to the 

 Purkinje cell layer. Occasionally, the vacuoles were arranged in vertical 

 columns. The vacuoles seemed to contain a protein-free aqueous solution, 

 because even with special staining methods and histochemical reactions no 

 other material could be demonstrated. Henceforth, the Purkinje cells, in 

 particular their nuclei, showed hydropic swelling. Within the swollen cyto- 

 plasm the Nissl bodies had usually disappeared. In other cells, the NissI 

 substance was dispersed as dust-like particles over the entire cytoplasm. The 

 Bergmann glial cells occasionally had swollen nuclei, but they seldom dis- 

 played any nuclear pyknosis. 



At 2 hours after 60,000 r, the regressive changes were still more advanced 

 (Figs. 1 and 2). Within the lower part of the molecular layer, the vacuola- 

 tion had progressed to tissue sponginess. Within the uppermost parts of the 

 granular layer, the tissue looseness had also increased. Some nuclei of the 

 irradiated granule cells were no longer swollen, but were shrunken and 

 pyknotic. Correlated with the decrease of the x-ray dose with distance 

 traversed, there was an upper zone composed mostly of pyknotic nuclei, 

 then a transitional zone with pyknotic as well as swollen nuclei, and a 

 lower zone containing solely swollen nuclei. Apparently as a consequence 

 of the pressure from the swelling of the molecular and granular layers, 

 many Purkinje cells within the center of the damaged area were deformed. 

 These cells were oval, and their longitudinal axes were parallel to the gran- 

 ular layer. In the lateral part of the irradiated field, several Purkinje cells 

 exhibited acute swelling. Near the border of the damaged area, which was 

 evident because of the changes in the granular layer, the Purkinje cells 

 showed slight or no morphologic alterations. 



