birds and rats have a marked effect upon the uptake of radioactive materials both in absolute quantity and in variability with different specimens. In those vertebrates where feeding 1s confined to the shore or a relatively restricted area the variability is less than where food is obtained from the water or over a relatively large area of the waters of the lagoon. In an area of strong water currents the variability in the specific activities in fish-eating birds increases greatly. The uptake of radioactivity by land vertebrates, however, does not appear to be in a state of flux as a result of the greatly modified environment as does that of the invertebrates. Rather the differences in amount and variability in uptake of radioactive materials is probably directly related to food habits. However, in areas of relatively great contamination, a tendencyfr saturation of the organs by radioactive materials rather than selective action upon the materials by the organs may confuse the interpretation of the latter. 4.8 Radiochemical Analyses Radiochemical analyses of post test samples of sand dredged from the bottom of the lagoon between Rojoa and Aaraanbiru, of beach sand from Engebi, and of soil from Rigili, Rojoa, and Runit were undertaken to provide a basis for comparison with results of similar analyses of biological samples. These an- alyses show the presence in about the expected ratio of all the important isotopes formed in fission except strontium, cesium, - 78~-