CELLULAR COMPONENTS: ELECTRON MICROSCOPIC STUDY 117 



change was observed in tliese structures. Again possible membrane defects 

 were extremely difficult to judge. The derangement of the ergastoplasmic 

 pattern in rat liver cells seen within 4 hours after whole-body X-irradiation 

 with 1,000 r (Fig. 4(a), (b)) was less obvious after local irradiation. No definite 

 early changes were seen in annulate lamellae. 



Cytoplasmic matrix and outer cell membrane 



As early as 1 hour after exposure, when nuclear damage is definitely 

 visible in many lymphocytes, several cells show cytoplasmic swelling. 

 Keliable morphologic evidence for cell membrane defects developing prior to 

 nuclear damage has not as yet been found. 



CONCLUSIONS 



The earliest changes in mouse lymphoid and bone-marrow cells after 

 whole-body X-irradiation with 600 to 1,000 r, detected in this study by single- 

 section electron microscopy, are found in the nucleus (chromatin derange- 

 ment with focal condensation and nuclear oedema). No comment is as yet 

 possible on eventual earlier membrane defects (nuclear membrane, mitochon- 

 drial membranes, endoplasmic emmbranes, outer cell membrane). Therefore, 

 and since radiation-induced membrane damage may occur within seconds, 

 we cannot — on the basis of our findings — evaluate the so-called "enzyme- 

 release hypothesis" of radiation injury. Further studies, including the appli- 

 cation of very short exposure times and serial ultra-thin sections, are necessary 

 to elucidate this problem. No morphological evidence is seen to suggest that 

 mitotic delay is due to radiation damage within centrioles. 



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 Bauer, W., and Stodtmeister, R. (1961). Unpublished data. 

 Bernhard, W., (1958). Exp. Cell Res. Sujopl. 6, 17. 



Bloom, W. Zirkle, R. E., and Uretz, R. B. (1955). Ann. N.Y. Acad. Sci. 59, 503. 

 Cleveland, L. R. (1957). J. Protozoal. 4, 230. 



DE Harven, E., and Dustin, P., Jr. (1960). C.N.R.S. (Paris). CoUoque No. 88, 189. 

 Glaxjser, 0. (1956). Schiveiz. Z. Path. Bad. 19, 150. 

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 Schneider, L. (1961). Protoplasma 53, 530. 



ScHRADER, F. (1953). "Mitosis." 2nd edn. Columbia University Press, New York. 

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