RADIATION INJURY ITS PATHOULNE SIS AND THERAPY 207 TABLE 3 Lhsoy SPE: IES Mouse Rat. Lo Guinea pig .. Rabbit .... Monker. . Dog . . TYPE Ob RAGEST ION . . . Swine ... Sheep. . Goat... Burro.. . . ' Absorhed dose 1m Tracts dose int mudventer 1250 KVP x-ray 443 638 , 250 KVP x-ray 251 200 200 2950 250 KVP KVP KVP KVP x-ray x-ray x-ray x-ray | 1000 KVP x-ray ' Gamma appron. 0.7 mev. . Ar expen tre 200 KVP a-ray Gamma approx. 1.1 mev. 640 337 S05 760 796 400 731 546 244 510 247 350 651 237 256 524 205 Representative LDgo per 30 day values for a numberof species are given in Table I (Bond and Robertson). The absorbed dose in rads is the siguifi- cant parameter that determines the degree of biological response. All mortality data in the table refer to conditions of exposure such that dose distribution throughout the bodyis essentially uniform, The dose at mudcenter has no particular significance except that it is convenient and represents the approximate dose that all tissues received (no single parameteris adequate to characterize an exposure under conditions of nonuniform dose distribution through the tissues). It can be seen at once from the table that the 1.D,,) values showno consistent pattern as air dose. Expressed as absorbed dose, however, the LDgo values for large animals are considerably smaller than for small species, and the degree of variation among species is less with large animals. The LD5¢ of man is not known with anv degree of accuracy; however, it is expected that for uniform whole body exposure the value is approximately 300 to 400 r, expressed as muidcentertissue dose. ‘The distribution of deaths as a function of time after irradiation varies with the dose of radiation and with species. For example, with the dog in the lethal range, the mean survival time is approximately 12 days, with deaths occurring 6 to 26 days after exposure. With doses of 1000 to 1500 r, some deaths occur earlier (8rd and 4th days) and the toxic symptoms of vomiting, anorexia, and diarrhea become more prominent. With doses of 1500 to 6000 r, all dogs die on the 3rd and 4th day. Severe diarrheais present. With the mouse, the distribution of deaths after irradiation with doses less than an LDso is essentially unimodal with peak of deaths occurring 11 days after exposure (Cronkite, Bond, Chapmanand Lee). In the LDgo range the deaths become bimodal with a peak at 4 to 6 days and another at 11 days 5012804 ,