the a and 8 chains contain 141 and 146 amino acid residues, respectively; thus the induced increase in isoleucine is 9.18 X 10> per R or 4.59 X 107° per polypeptide per R. 5 in the two polypeptides Moreover, there are 20 different amino acids and the average of these would be expected to show a similar increased frequency of substitution for other amino acids as a result of radiation-inducec, base substitution mutations; thus the total induced amino acid substitution frequency would be near 9.18 X 1074 per polypeptide per R. This suggests that for acute exposure the average frequency of induced point mutations at the hemoglobin loci in the erythropoietic stem cells of man may be about three orders of magnitude greater than induced mutations in cS on = cn (aa cn germinal celts of mice detected by the-specific locus method !?,