THE SHORTER-TERM BIOLOGICAL HAZARDS GF
a linear effect of about 0.3 percent per raentgen,
if you put it on a per roentgen basis. This, as
T say, is over an enormous range of radiation
exposure.
Now, this means, then, if you transform a
little further that approximately in terms of
the hit theory you have about 2 to 3 cells
injured per 1,000 cells per 1 r of radiation
exposure. If you test this out a little bit
further in terms of what we know about the
genetic effects of radiation, the genetic effects of
radiation in terms of mammalian system, gives
you at the level of 50 roentgens a mutation
induced in about 1 cell out of 10 germinal cells.
Then you multiply these two together, and you
find per roentgen this means about 1 mutation
in 500 cells or per 1,000 cells this is an induction
of I new mutation of 2 cells out of every 1,000
cells exposed at the level of 1 roentgen. So
that you see in terms of a system that we
knowthat leads to immediate radiation damage
in terms of the killing of cells associated with
radiation effect, that both the genetic effect and
the killing effect of cells per roentgen are the
same order of magnitude, and thus we can very
easily see a unifying bridge between these two
systems of information that we can study.
In one case the manifestations per surviving
cell are rather subtle in character, and in
another effect with relatively large number of
cells killed as you would have about the 50
percent lethal dose of radiation exposure which
extends from. about 200 to about 500 roentgens,
physiologic geucration of symptoms involved in
such effort.
In Ceriof the recovery potentiality of these
particuli, tissues, the lymphatie cells, the
marrow, vou have a great eapacity of these
cells to regenerate and replace the damaged ones
that «re killed. As a matter of fact, the daily
replacement of such tissues anyway is of the
order of 10 percent replacement por day. So
even at the levels of one r, 10 r or 100 r, the
radiation induced damage is not an enormous
burden compared with the ordinary replacements of such cells in such tissues. So if this
were the level that we could view radiation
effeet, 1 think we could be quite comfortably
assured by the fact that the tissue potentiality
of replacement is one that would lead us into a
threshold effect of radiation and a very com-
fortable one, because we ought to be able to
replace thege cells,
effect, and thatis the absolute numbers ofcells
that may be involved. The amounts may be a
qualitative difference in the kinds of cells that
are left on the average after radiation exposure,
andareleft on the averageafter the aging effect
proceeds,
sition of transformations of the cellular information on @ mutational basis so that wo could
explain it on the basis of somatic cell mutation,
accumulating with age. Tt is such a tempting
strongly suggests that for such tissues as the
the whole aging phenomenonin terms of acqui-
system, indeed, because almost all the data that
we have to work with fit. Nowever, thore is
still another thing that we can work with from
the standpoint of change with age on irreversible
There may bea changein the absolute numher of cells that. survive within a given individual cither as a function of age or radiation
exposure,
The best information we have along
this line is {he information that Nathan Schott
of Baltimore has collected for man, which
kidney, and perhaps the body as a whole, that
there is a decrease jn active cell numbers
amounting to about a 6 percent decline per
decade for human tissues. This follows quite
linearly over the whole of the measurable life
span.
So a combination of this perhaps with
the change in the vigor of cells would certainly
8
The trouble in the problem
as far as radiation effect at subtle levels is
concerned, that the cells that do survive very
likely will carry with them the same quantitative transformation of the nucleic protein
structure as the germinal cells in terms of
mutation.
This would then be per roentgen at the generation of 1 or 2 new mutations per 1,000 cells.
So that the surviving cells that fill and replace
the celle that are damaged supposedly survive
with this kind of a transformation of their
inherent vitality. I think that this is where the
genetic effects of radiation have a great deal in
common. As far as we know, in critically
testing these systems, we can be uncertain as
to whetherthe life subtracting effect of radiation
a
significant results. You find that over this
whole range, even though youare dealing with
different species, for these three tissucs, the
effecta between the mouse, rat, and rabbit and
man are that per roentgen on a log scale of
surviving tissue as a function of dose, you have
of cells killed, aid of course quite a great
121
effect as to whethertheeffect is given all in one
dose or is fractionated.
This, of course, is the viewpoint that one
largely takes for (he total mass formationof the
total genetic offects from radiation where the
total transformation of the genetic information
is per roentgen and does not depend upon
dosage rate.
Howwoefinally interpret the life subtracting
effects of radiation, I do not know. It would
be very, very tempting at this time to place
a
_ haps direct measures of mytosis or turnover of
these cells in a measuring system.
If you takeall these together with respect ta
dose you have a range of dose that extends
from about 2,000 r at the upper end, down to
about 15 rat the lower end, where you can get
DISCUSSION ON TOPIC IT
FALLOUT PIELD
MILLION PER c.mm. x 408
to time after dose, perhaps the concentration
of these cellular elements in the blood, or per-
4
depending upan (lie species, a very large number
IRRADIATION DOSE
GROUP
S
120
the total cellular mass that. is left with respect
is entirely linear in terms of whether a divided
dose or a single dose give the same effect.
EAGH POINT IS THE AVERAGE COUNT OF TEN
ANIMALS UNLESS MARKED IN PARENTHESES
Dr. Blair has just shown you some results on
this. There is an entirely allowable viewpoint
that a single dose may have 2 or 3 or 4 times
the effect of a smaller rate of dose.
But the
statistics that all of us have to work with are so
limited in their character that it would still
permit a more unifying viewpoint that it does
not make any difference for the life subtraction
TOTAL r
410
14
843
687
1000
NONE
Qo
2
4
6
8
10
'2
14
WEEKS POST IRRADIATION
RED BLOOD CELLS, IRRADIATED AND CONTROL SURROS
Fiaure 1.—Red blood cells, irradiated and control burros.
6
{8