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