REPAIR ASSOCIATED WITH EROSIVE EFFECTS OF FALLOUT IN INDIVIDUALS, GROUPS
OUT FIELD
GICAL HAZARDS OF A FALL
THE SHORTER-TERM BIOLO
90
most of the mutations (hat persist are of the
deleterious Cype involving reduced cellular
efficieney and leading to reduced organ and
organism efficiency, there exists a means not
te f doy
8
5r/ doy
only for the persistence of irradiation effects
throughout. Hfe, but also for degenerative
changes that lead to carlicr limes of death. As
& consequence of irradiation, defective mutant
200 / day
‘rT
et
cells He scattered at random throughout the
growing tissue elements, These are in competi-
=
6
tion with nonmutated cella in the samelocal-
3.1
ities and it is necessary Lo assume thai at least
part of these are successful in starting strains
of cells that develop inio scattered islands of
cells, some widely separated and others over-
a
lapping and even diffusing into cach other.
1
The net effect over time is a gradual tissue
z
a
*
6
3
10
rf
49
20
6
80 10
200
4000-600
transformation, involving at the same time
ae
7 800
a point of organ failure in a vital part.
DAYS
otracted exposure,
Fiavern 3.—Work capacity—-Pr
type of
life. ‘This we identify as the first
The conseerosive effect we have in maind.
80
rative motor,
quence is a racing of the regene
of a portion
to speak—actually, a consumption
is drawn
of the regenerative reserve which
;
s. —
uponin the ease of body emergencie
dered is
The second erosive effect to be consi
t exists as
very different in character. Thati
, bul as
a reality there is no longer any doubt
for it is somewhat
yet the experimental proof
casily by
sketchy. Tt can be identified most
as set off
reference to the Intermediate Phase
exposure
in Figure 1. If damage from acute
post. irradiation
has not been too great, the
ent normality ~
sickness phase is one of appar
inversely
yet the length of this phase varies
even before
with the size of dose administered
in mind that,
the sickness developed. Bearing
approach nortissue replacement appears to
elimination to
mal, attention is drawn by
45 & basis
residual quality of the growingtissue
process.
for understanding the life shortening
modified
It is known that cells are killed or
tion of bioas a result of irradiation by induc
(a very
chemical changes and/or mutations
The erosive effect in this case is secondary to
e). It is to
specific kind of biochemical chang
must be probe presumed thatlife shortening
uch as the
duced by the same means inasm
ional changes
induction of biochemical and mutat
which radioappear to be the main means by
ed. . Choosing bebiologic changes are induc
s, it appears untween these two possibilitie
es, which oe
likely that biochemical chang
if
dance W
produced so very precisely in accor
should persist
ure,
expos
of
time
the
at
dose
gh the comwith the same precisencss throu
Intermediate
paratively quite Jong Acute and
y in the TermiPhases to cut off life prematurel
change as
nal Phase. This leaves mutational
change that prothe most likely radiobiologic
and premature
vides a link betweenirradiation’
later.
which occurs months or years
As
death
plausible basis
will be secn, it also provides a
, anda
ining radiation life shortening
for expla
fied as a thir
the same time, what is identi
wpe of erosive action.
reduced organ efficiency. Death is the natural
consequence whentissue transformation reaches
.
radiation produces
* Since it is known that
cells, that certain of
mutations in proliferating
fore
and there
the induced types are sublethal
n, and that
able to continue with proliferatio
the initial irradiation effect and involves
sirictly biologic action-—the multiplication and
spread of less efficient mutant cells. With continued power to proliferate, but with reduced
power to perform specialized functions as re-
quired by the host organism, the organism is
jeopardized increasingly so far as its ability to
cope with the rigors of life is concerned. For
this type of erosive effect—to the extent that
is exists—recovery consists of competition between the normal and mutated cells or tissues,
and insofar as growth of normal tissues domi-
91
Mutations are produced in germ-line cells of
the reproductive system the same as in other
proliferating tissues.
The mutations induced
in both cases consist of three types: The /ethal,
which culminate in early cell death and thus
drop outof the picture very quickly; the del-
eerious, which are responsible for reduced
efficiency in cells so far as well-being of the
organism is coneerned, but not for preventing
proliferation; and the comparatively very rare
beneficial type. Deleterious mutations, as a
consequence of mitosis of affected cells and of
breeding, become spread in the aggregate germ
plasin of the population--sometimes called the
gene poot-—in much the same way that they are
spread in individuals by proliferation alone.
Deleterious mutant cells, both in the germ line
and in the soma, multiply and tend to exert in-
creasingly depressive effects on vigor and
stamina~—vigor and stamina of the population
group in one case, and of individuals in the
other.
An important difference, however, is
that in populations there is opportunity for
selection of the type that, in connection with
mating, favors the more able and discriminates
against the less—a type of process for which
there is no counterpart in individuals.
Favor-
able selection is henefited additionally by
retention of any beneficial mutations that occur.
The fact that selection can occur at the popu-
Jation level and that such does not occur in
connection
with
mutations
in
individuals,
furnishes some explanation of why species have
the opportunity of living on indefinitely whereas
nates growth of the abnormal, it can be said
that repair takes place. But, of significanceis
organisms must. inevitably die.
The erosive effects involved here are similar
takes place, is also systematic and hears a close
acting this influencein such a way as to main-
the fact that there is a systematic correlation
between size of dose (acute) and amount of
life-shortening. This means that repair, if any
relationship to the amountof effect produced.
The third type of erosive effect to be consideredis still different in character. It involves
effects on populations rather than effects on
individuals alone. Of significance here, radiation appears to act on population groups in
much the same way that it acts on individuals
but with certain important differences.
448020 0—58—~7
to those of the first type described, in that continuous irradiation tends to use up or consume &
reserve, and that recovery consists of countertain a suitable margin of safety.
In obtaining
the benefits of variation that stem from the
induction of mutations ai random, by irradiation or otherwise, and from the selection which
goes along automatically, it is obvious that a
certain load of deleterious mutations is carried
more or less continuously. It is obvious also.
that population groups can carry a given load