16 Hemopoietic reserve. It was of interest to determine whether the hemopoietic reserve of the exposed Marshallese was equal to that of the unexposed group. Means were sought to stimulate 2) MN System: This blood group system was distributed as follows. No. or challenge the marrowin regard to white cellular elements, erythroid cells, or platelets, but no feasible methods have been found. However,ad- vantage was taken of a possibility that effects of the natural stress of menstruation and childbearing in the women 15 to 45 years of age might be reflected in differences in levels of their peripheral blood elements. The bloodlevels in this group of females were compared with those in the same age group of unexposed females, and the differences were then compared with the differences between exposed and unexposed men in the same age groups. Irradiated women and men,15 to 45 years of age, were foundto showthe following per- centage differences from the unexposed women and men of the same age group: neutrophils, females —5%, males +3%; lymphocytes, females —6%, males —15%; platelets, females —6%, males —7%; hematocrit, females +2%, males —6%. From these data, it did not appear that exposed womenshowed anylowerlevels of peripheral blood elements than did the exposed men compared with the unexposed groups, and the stress of these female functions did not appear to cause any noticeable effect. Hematological Studies of Genetically Determined Traits. Blood grouping studies. The followingis taken from a report by Sussmanetal.'® on blood groupings in the Rongelapese. M MN N 8 20 101 % GENE FREQUENCY 6.2 15.5 0.14 78.3 0.86 The low frequency of the M gene has been noted in the Marshall Islanders by many investigators." The frequencies obtained in this study are amongthe lowest encountered. 3) Rh-Hr System: A most unusualdistribution was noted in this system. Tests were performed with anti Rh, (D), rh’ (C), rh” (E), hr’ (c) and hr’ (e) sera. The results are as follows. PHENOTYPE No. % CHROMOSOME FREQUENCY Rh,Rh, Rh,rh 126 3 97.7 2.3 R'=98.5 The chromosomefrequency of 98.5% for R' is the highest reported for any ethnic group. The complete absence of any rh negative personsin these and related series leads one to suspect that the true genotype of the bloods giving a positive reaction with anti hr’ (c) serum is most probably R'R*. The occasional finding of an Rh, person by Simmons*® supports this interpretation. In the present series of 125 there were no bloods that reacted with rh” (E) antiserum. 1) ABO System: The groupings in this system were as follows. Group oO No. % GenE FREQUENCY 75 358.1 0.762 0 0 A, 24 B 19 A,B 10 A, A.B 1 18.6 15.0 0.114 0.093 p.=0.789 Case No. Age Sex WBC (x10%*) q.=0.116 7,= 0.095 74 0.8 The unusual finding of a single A.B was verified by testing with several absorbed B antisera, as well as with the lectin of Delichos biflorans.'* The total absence of A, genes in Eastern Asia, Australia, and Indonesia has been repeatedly noted.'*** Inquiryinto the family backgroundofthe single A.B native failed to reveal any significant information leading one to suspect admixture. Table 7 Neut. (x1O7) Lymph. Plate, «10 ') («10° H EXPOSED 68 73 53 22 M M 4.6 4,7 2.2 2.3 1.7 2.1 199 198 3 4 12 16* 58 30 11 23 42 63 63 54 F M F F M 4.5 4.5 5.6 5.5 5.6 1.6 2.2 2.2 3.7 3.2 2.8 1.8 3.2 i 2.2 316 247 219 197 218 3 4 3 3 3 UNEXPOSED B78 39 M 5.0 2.2 2.2 229 4 854 58 F 5.1 2.2 2.7 383 4 *Ailingnae.