Fliedner, Cronkite, Bond and Andrews
459
Material and Methods
On June 16, 1958, eight men were exposed to mixed neutron-gammaradiation. Five of
them received doses between 236 and 365 rads, three of them received 23 to 69 rads. Bone
marrow aspirations * were performed 12 hours after the accident in the ‘heavy dose” group of
five and from then on at about twice weekly intervals for four weeks. Marrow aspirations were
donein the ‘low dose’ group approximately once a week.
Summaryof the Hematologic Findings. Details of the accident and of the hematologic data were
reported by BruceR (1959) and the overall picture of the mitotic activity by FLIEDNER et al.
(1959): the total white count remained at high normal values for two days, then decreased
until about the 9th day. Between the 9th and 16th day there was a slight rise in the total white
count. Minimal levels were reached about the 29th and 30th day, with subsequent rather
rapid recovery. Giant neutrophils appeared in the peripheral blood after about 4 days. Lymphocytopenia was present within 48 hours after exposure in the “heavy dose’? group. The numberof
. platelets remained within normal limits during the first 15 days and then showed a progressive
decrease reaching lowest levels between 25 and 35 days. The hematocrit remained within normal
limits in 3 of the “heavy dose” group andfell below normallevels in 2 during the Sth week.
The mitotic index was determined in Feulgen stained squash preparations*. A first
minimum was reached after about 4 days and on this day a clearcut dose dependency was
noted, There was slight increase in the mitotic index around the 8th day. A second minimum
was reached in the 3rd week. Normal proliferative activity as indicated by the mitotic index
was reached in the 5th week, at the time of the most severe depression of the number of blood
cells. Four and-one half months after the accident, the mitotic index was significantly above
normal limits.
Results
Radiation Effects upon Cell Division. The number of mitotic figures per 1000
nucleated bone marrow cells during the first 4 days was counted in ordinary bone
marrow smears (Fig. 1). The mitotic index in the ‘heavy dose” group marrow
smears fluctuated considerably. In the 12 hour sample a slight depression, and in
the second sample a slight increase is possible but this was notsignificant before
the mitotic index reached low levels.
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DAYS AFTER EXPOSURE
Fig. 1, Mitotic index in bone marrow smears after accidental irradiation
(Normal: 5 per 1000; Jara, 1942).
* The marrow aspirations were performed by Dr. KretscHMar of the Oak Ridge Institute
of Nuclear Studies, whose cooperation we gratefully acknowledge.