epithelial REPAIR ASSOCIATED WITH EROSIVE EFFECTS OF FALLOUT IN INDIVIDUALS, GROUPS THE SHORTER-TERM BIOLOGICAL HAZARDS OF A FALLOUT FIELD sloughing in the months; and (4) that the acute reaction of degeneration and repair (Phase I) is followed bya long period of apparent normality (Phase 11) and, in turn, by a terminal period (Phase TII)--which, aside from infections and accidents, involves degencrative diseascs and neoplasia mainly, Inherent, but not made evident gastrointestinal tract, hemorrhage, bloodclotting failure, epilation, sterility, cataract, etc. It is of practical, and also some scientific, significance to deal with the net effects of radiation in individuals and in population groups, as a means of gaining a. Reserve energy-—ability to do a 10-mile march. &. Normal work—-ability to perform a regular day’s work. ec. Lassitude and easyfatigue. d. Milnes (sickness, discomfort, anxiety) but capable ofself care. Phaseis foreshortened by exposure to radiation, and that the Terminal Phase involves the same kinds of features as are present irrespective of radiation. of people can do followingirradiation. Implications of Figure 1 are: (1) That the growing tissues work capacityorillness as follows: bythe figure, is the fact that the Intermediate impressions of what individuals and groupings necrosis in were chosen to represent different levels of e. Illness, but with need of nursing care. These terms or expressions were then ar- Dealing with short duration exposures (minutes, seconds, or less), Figure 2 pictures performance ability during the Acute Phase— (bone marrow, lymph nodes, spleen, gastrointestinal epithelium, germinal epithelium of the testis, and skin) is precipitous following near lethal irradiation exposures; (2) that if the necrosis is ranged on a scale in order from 6 downward, respectively, as shown in the figure, and, on the basis of clinical, hematological and histo- the phaseof tissue necrosis and replenishment (especially in the gastrointestinal tract and hemopoietic organs). The scale for performance ability—work capacity as it is labeled—is some- excessive, death will result; (3) thatif it is not too extreme, repair by means of mitosis and pathological information, choices were made as to the level at which the majority of people exposed would be expected to exist at different times after different acute exposures. what arbitrary, but, as will be seen, is never- theless useful. It was developed in the following manner. Deacriptive terms or expressions tissue replenishment will take place, reaching the normal range in a matter of weeks or } ‘This gave the curves as shown. Since some interpolation was necessary to obtain smooth curves and since the descriptive terms did not haveprecisely uniform quantitativesignificance, the values on the scale cannot be said to repre~ sent the descriptive terms concretely or vice versa. The development as a whole, however, gives a consistent picture, and one that has meaning. In terms of integrated effects of near lethal dose of radiation of short duration on the body as a whole, the following can be said: (1) That there is an immediate condition of sickness or shock; (2) that the degree of illness varies 10% SURVIVING WORK CAPACITY directly with dose; (3) that the iliness may be DAYS Fiaurx 2,—Work capactty—Acute exposure. a 200 400-60 1000 any dramatic effects at the beginning, but work capacity falls with accumulation of the integrated effects. Tmplications of the curves are: (1) That for doses of 20 r per day, work capacity becomes noticeably reduced in 2 to 3 weeks with death occurring as an end result at about 2 months; (2) that for doses of 5 r per day, reduction in work capacity is barely gradually with death occurring in 3 to 4 years; and (3) that for doses of 1 r per daythere is no noticeable reduction in work capacity in 3 years time. Of importance in connection with protracted radiation is the fact that damage and repair— moreparticularly, cell destruction and replacement-—go along togetherin the growingtissues, and also the fact that defects in the organism begin to show only when the rate of destruction exceeds the rate of repair. From Figure 3, there is indication that the threshold of injury to the organism, so far as work capacity is con- cerned, is about 1 r per day, and from this it follows that the resiliency of the growing tissues in general—that is, their maximum capacity to regenerate—must be offset or counteracted effectively by radiation doses in the neighborhood of 1 r per day. How great the resiliency of tissues may be and how much reserve capacity exists in at least some of the organs, are indicated by the following facts (developed from animal experi- ments mainly): Three-fourths of a liver can be removed by surgery and a whole liver will regenerate; one and a half kidneys can be extirpated without reducing normal excretory effi~ (5) that during the fourth week, recovery sets drawn off every two and a half weeks (i. e., in (in survivors), which then for certain organs ovennetbneerelvarleandac 40 60 BD 100 plan as employed in connection with Figure 2. Here a shock response is totally absent due to less during the second to fourth or fifth days; (4) that during the second and third weeks there is a precipitous fall in fitness which coin- cides with the cascade of tissue necrosis; and nm 8&9 noticeable in 3 months but that it does fall f. Death. oe ee 88 which probably would be typical for most or all mammelian forms. The figure gives orientation also with respect to the integrated effects of key reactions, such as the blood dyscrasias, (gastrointestinal and hemopoietic which in particular are of vital importance) reaches the normal range in 2 to 4 months. Turning to protracted or intermittent exposures, Figure 3 shows performance ability at different times in connection with daily treatments of different amounts, using the same ciency ; and a full body content of blood can be blood being removed at intervals during such periods) without distortion or reduction of the peripheral blood picture. On the basis of such information, it would seem that the subthreshold or subliminal effects of protracted irradiation may bequite large in terms ofcell destruction and replacement—that is, beyond that which takes place during the normal course of