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F. STEPHEN VOGEL 



further contraction of the nuclei, the intranuclear material was greatly 

 compacted, but still remained particulate and discrete, the granules being 

 separated from one another by an electron-lucent margin of uniform width. 

 Although the nuclear membranes became redundant with extreme contrac- 

 tion of the nuclear mass, in the rabbit they did not fragment, but folded 

 and coiled. The expansion of the cytoplasm was conspicuous, in most cells 

 exceeding the volumetric decrease in the nucleus. The over-all size of the 

 cells increased. The endoplasmic reticulum was widely dispersed in the 

 expanded cytoplasm, but did not show consistent structural change (Fig. 6). 

 The recovery phase, as judged by light microscopy, was completed by 72 

 hours after radiation. Tissues taken at this time and examined with the 



Fig. 6. Electron micrograph of a pyknotic granule cell of a rabbit 24 hours after 

 exposure to 15,000 r of gan.ma radiation. The nucleus of one cell is extremely con- 

 tracted; the intranuclear granules are condensed and the cytoplasmic space ( f ) is 

 greatly expanded, with dispersion of the cytoplasmic constituents. Two unaltered 

 granule cells and a capillary surround the pyknotic one. Approximately X 10,000. 



