a7 mass and/or total blood volume with total body weight used as a base line. During the 1963 survey, Rongelapas result of their fallout radiation exposure. Attempts at 8 and 9 years post exposure to obtain suitable blood cultures had not been entirely successful. However, during the 10-year survey a slight modification of the Moorehead technique’® resulted in a series of satisfactory similar studies were performed on 21 Marshall Islanders, but these data were related to total body water as determined bytritiated water.*® Results showedthat in all instances but one the values for red cell mass and total blood volumefell below normallevels for persons living in temperate zones of the United States. The present study was undertaken during the cultures on 51 people: 30 in the higher exposure group (175 rads), 13 in the lower exposure group (69 rads) and 8 from the unexposed Rongelapese who were on another island at the time of the accident. Thedetailed results of these studies are surveys in 1965 and 1966. A total of 19 Caucasian Americans (3 females and 16 males) living in the Marshall Islands for periods of 3 monthsto 9 years were examined bythe same techniques.* There- presented in Appendix 14.* Table 25 summarizes the results. A higher in- cidence of aneuploid cells was noted in the exposed group, butthe difference was not great enoughto be significant. Unexpectedly, the lower exposure sults of these studies on each individual are pre- sented in Appendix 15, along with data on the 21 Marshailese in whom these studies were carried out in 1963. The data were programmed and Oat wall group showed more aberrations than did the more heavily exposed group,and the latter group showed even less aberrations than the unexposed. However, the incidence of 2-hit aberrations wassignificantly higher ( <(0.004) in the exposed groups and did appear to be radiation induced. Figure analyzed by a high speed digital computer. Re- gression lines obtained for the Caucasians and the Marshallese are presented in Figure 67 along with regression lines ofMoore’andSiri"* for Americans. The Marshallese regression lines for both blood 66 shows a dicentric and a ring form noted in chromosomespreadsfrom two exposedindividuals. volumeandred cell colume have very nearly the same slopes as the lines of the Siri and Moore native environment have shown reducedredcell groups, but thev are significantly below the latter (significant at the 1% level). The Caucasiansliving in the Marshall Islands also show regression lines for blood volume and red blood ceili volume with slopes similar to those of the Marshallese and the Siri and Moore groups. Comparison of the regres- *We are grateful to Dr. Shields Warren and his eroup at the Cancer Research Institute in Boston for carrying out the chromosome analyses. carrying out the tritium-water analyses. OTHER LABORATORY STUDIES Total Blood Volame and Red Cell Volume Previous studies (1961, 1962) with °'Cr-labeled ervthrocytes on Marshallese subjectsliving in their sion lines showsnosignificant difference between *Weare grateful to Dr. W.E. Siri, University of California, for Table 25 Summary of ChromosomeFindings No. of persons No. of cells scored Percent of cells with 2n3446 Exposed 175 rads 30 1500 10 Exposed 69 rads 13 650 8 8 400 3.5 Group Unexposed No. of persons with aberrations Chromosomeaberrations Total aberrations Totai cells with aberrations 5 22 (1.46%) 20 (1.33%) 43 15 1 8 21 (3.23%) 18 (2.77%) 31 4 - - 6 5 Fragments Dicentrics Rings Exchanges 12 (40% ) 11 6 - 11 (84.6%) 10 2 9 - 5 (62.5%) 9 (2.25%) 8 (2.0%) ChroIsomatid chromand breaks gaps