ee
otdeus well below the lethe! rangs,aad increase
ing dese.reseits in ne or minimal further de
crease in count. Lymphocyte depression appears te have ne causal relationship with ecute
radiation deaths.
pesure but for which centrel humatalegical
valuce were considerably dificreut (the |ymphecyte count is net seitable fer comparisen since
dagres of depression wan ensentiaily the aame
extensively in dogs (90). As with newtrophiles,
group). At the time ef peak depression fer
he
ec) Platelet counts have been studied most
Re oo eee Aig ey er
the rapidity and magnitude of depression is 8
function of dese below the lethal range. Maxi-
mam depreesion occurs by the Sth ct 10th day
with doses in the high lethal range, by the 10th
to 15th day at sublethal levels. Recovery be-
gine during the 3d week, but is not complete by
ory
ee ee
eees cere
the 30th day when most studies have been terminated. Insufficient data are available to indicate the time required for complete recovery.
Considerable evidence incleding studies in
the mouse using splenic homogenates, induced
bacterial infections and
infections
have indicated that critical neutrophile levels
exist, below which survival is correlated with
the absolute neutrophile count following wholebody irradiation (15). From data on dogs, it
spective contro] values. Thus, some evidence
is afferded thet abeolutc counts, rather then
counts relative te contrel values, may be the
more reliable index of expesure in thie dase
range.
445 Apprenimaticn of Miniaal Lethal Dees fer
Men
Some indication of severity of exposure cam
be gieaned froma comparison of minimums imdividual counts in Japanese groups in which fatalities occurred.
In general, a significant
50,000 or below.
percent had counts below 1000.
Platelet data on dogs indicate that animals
with external purpura have platelet counts of
Sufficient data on large animals sre not as
yet available to quantify the extent of maximum depression of either the neutrophile or
platelet counts as a function of dose in the sub-
of dose in the sublethal range are indicated.
It is not possible to say at present whether
severity of exposure, or of radiation damage
ee
each element, the neutvephile counts wore
exsentially identical in terms of absolutecounts,
but considerably different in terme.of the re-
number of deaths was encountered only in individuals whoee neutrophile count fell below
1000. In GroupI, 42 or approximately 50 percent had neutrophile counts below 2000 at some
phocyte counts. For the preceding reasons,
systematic investigation of the platelet and
leukocyte counts in large animals as a function
i
im these groups and the higher-dese Rengrisp |
appears that survival is likely unless neutrephile counts remain below 1,200 cells for a
period of time.
lethal range. The response of the platelet count
in the present study was much lees subject to
fluctuation than were the neutrophile or lym-
ee”
which hed esmatially the sine ealeulated an-
correlates better with absolute levels of periph-
eral blood count, or with degree of change
from control or pre-exposure levels. Some
evidence on this point can be gained by comparing the degree of depression of the neutrophile counts in (:roups II and LII, bath of
2} SMe
~
a
time during the observation period, and i0
By this cri-
terion, then, the effective dose received by the
Rongelap people approached the lethal range.
In the dog (Cronkite and Bond, unpublished
data), approximately an additional 50 to (00 r
are required to lower the neutrophile count by
1000 cells mm? in the high sublethal dose range.
If these data can be applied to man, an additional 50 to 100 r would have placed the dose
well in the lethal range. On the other hand,
however, it is clear from the present data and
from clinical experience with therapeutic radiation that neutrophile counts between 1000 and
2000 in human beings are in general well toler-
ated.
Human beings with these levels of new-
trophiles show no clinical evidence of ilineas,
are physically active, and generally do not need
prophylactic antibtotic therapy.
The people of (;roup I are estimated to have
received 175 r ax calculated from dose rate read-