of Human Bone Marrow after Accidental Exposure to Ionizing Radiation
467
11. Honzt, K.: Experimentelle Untersuchungen tiber Réntgeneffekt und chemische Effekte
auf die pflanzliche Mitose (Thieme, Stuttgart 1949).
12. Layrua, L.G.; Ourver, R. and Exuss, F.: Effects of irradiation on DNA synthesis by human
bone marrow cells in vitro. Advances in Radiobiology, Proc. Int. Conf. Radiobiology
(Oliver and Boyd, London 1957).
13. Weicker, H. and Terwec, K.H.: Die Chromosomenzahl der Erythroblasten. Klin. Wschr.
36: 1132-1138 (1958).
14. Wenpt, E.: Lebendbeobachtungen an bestrahlten Interphasekernen. Z. Zellforsch. 49:
677-689 (1959).
Discussion
D. Pecoraryi (Pavia, Italy): It is known that variations of the mitotic index may depend
on (1) the mitotic rate and (2) the mitotic duration. It is possible that in the cases described
mitosis is prolonged as shown by the high number of morphologic abnormalities observed.
I ask therefore if evaluations of the mitotic duration have been made?
Secondly, we have observed by phase contrast cinematography in new erythroblasts
that giant nuclei with or without morphological abnormalities often derive from metaphasic or
anaphasic nuclear reconstruction leading to polyploid nuclei. I ask if Dr. FLrepner has also
seen these abnormal nuclear reconstructions?
T. M. Frrepner (Reply): It was impossible to study the time of mitosis in these exposed
men directly. Butit can well be that there is a delay in the mitotic time resulting in an elevation
of the mitotic index.
Studies on irradiated rats indicated an accumulation ofcells in the second rest-period,
before onset of mitosis. After about 18 hours (750 r) the mitotic block is overcome and this
results in a mitotic index within normal levels. Abnormalities in blood cell precursors show
a wide variation from impaired nuclear division to long chromosomebridges. Many of these
cells die before they can mature to becomecirculating blood cells. But a few do and it seems
to depend onthe stage of the precursor in which the damageoccurred whatsize and ploidy the
maturecell has. Someof the erythropoietic precursors shown might be due to the process which
Dr. Pecorari indicated.
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