37 mass and/or total blood volume with total body weight used as a base line. During the 1963 survey, similar studies were performed on 21 Marshall Rongelap as result of their fallout radiation ex- posure. 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 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. The detailed results of these studies are presented in Appendix 1I4.* Islanders, but these data were related to total body water as determined by tritiated water.’® Results showed that 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 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 Table 25 summarizes the results. A higher in- were examined by the sametechniques.* There- cidence of aneuploid cells was noted in the exposed group, but the difference was not great enoughto be significant. Unexpectedly, the lower exposure sults of these studies on each individual are presented in Appendix 15, along with data on the 21 Marshallese in whom these studies were carried out in 1963. The data were programmed and analyzed by a high speed digital computer. Regression lines obtained for the Caucasians and the Marshallese are presented in Figure 67 along with regression lines of Moore" and Siri‘ for Americans. The Marshallese regression lines for both blood volume and red cell colume have very nearly the same slopes as the lines of the Siri and Moore groups, but they are significantly below thelatter (significant at the 1% level). The Caucasiansliving in the Marshall Islands also show regression lines for blood volume andred blood cell volume with group showed more aberrations than did the more heavily exposed group, andthe latter group showed even less aberrations than the unexposed. However, the incidence of 2-hit aberrations was significantly higher ( p <0.00+4) in the exposed groups and did appear to be radiation induced. Figure 66 shows a dicentric and a ring form noted in chromosomespreads from two exposed individuals. OTHER LABORATORY STUDIES Total Blood Volume and Red Cell Volume Previousstudies (1961, 1962) with *'Cr-labeled erythrocytes on Marshallese subjects living in their native environment have shown reducedred cell slopes similar to those of the Marshallese and the Siri and Moore groups. Comparison of the regression lines showsnosignificant difference between *We are grateful to Dr. Shields Warren and his group at the Cancer Research Institute in Boston for carrving out the chromosome analyses. *We are grateful to Dr. W.E. Siri, University of California, for carrying out thetritium-water analyses. Table 25 Summaryof ChromosomeFindings Group No. of No. of cells Percent of cells with persons scored 2n5=46 Exposed 30 1500 10 Exposed 13 630 8 8 400 3.5 173 rads 69 rads Unexposed 50068341 No. of persons with aber- Chromosomeaberrations Frag- Dicentrics Rings changes 12 il 6 ~ i) 11 10 2 l 8 5 9 - - - rations (40% ) (84.6%) (62.5%) ments Ex- Total aber- rations 22 (1.46%) . 21 (3.23%) 9 (2.95%) Total cells with aber- ChroIsomaud chromatid rations breaks gaps 20 43 15 18 31 4 8 6 5 (1.33%) (2.77%) (2.0%)