The least variability in organs and tissues of the postshot rats was found in the liver, the variability of kidney and lung being slightly greater. When the average values for each organ or tissue of the postshot rats are compared, muscie is the lowest, and bone is the highest in activity of the samples taken. “ung tissue, however, is almost as low as that of muscle tissue. In the birds from Rigili, Rojoa, Aaraanbiru, and Runit, the lowest activity was found in the muscle. In the same birds the highest levels of activity were in the gut, or digestive tract, with the exception of Rigili, where the bone contained the greatest amountof activity. In birds from the southern islands of Igurin, Japtan, and Eniwetok, the lowest levels of activity were found in the liver. The highest levels for birds of these islands were found in both the skins and bones and were approximately the same. Judging from the data from both birds and rats, muscle either takes up or retains a lesser amountof radioactive material than any other tissue or organ sampied. In rats radioactive materials are deposited in the bone with greater facility than in any other organ or tissue sampled, Evidence that this is not a general uptake by the bone, but rather a selective action, is indicated by a mass-absorption curve of one of the six specimens taken at Biijiri (Fig. 4.10). Inflections in the curve indicate that the beta particles having maximum energies of approximately 0.2, 0.8, and 1.3 Mev are present. A mass-absorption curve of a noddy tern bone specimen (Fig. 4.10) gives some indication of selective deposition in uptake by bone. Well-defined inflections which were evident in the rat-bone sample are not found; however, the presence of beta particles having maximum ener- gies of approximately 0.4, 0.95, and 1.3 Mev are suggested. 4.7.7 Conclusions Feeding habits, as well as the range of activity of 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 whose feeding is confined to the shore or a relatively restricted area, the variability is less than in those whose 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 ina 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 are probably directly related to food habits. However, in areas of relatively great contamination, a tendency for 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 posttest 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 analyses show the presence in about the expected ratio of all the important isotopes formed in fission, except strontium, cesium, and rubidium. Cesium and rubidium are water soluble and could be expected to be leached out of the sand and soil samples. A probable reason for the absence of strontium in the expected amount is not clear. Radiochemical analyses were made of the following ashed biclogical samples: plankton, algae, octopus gill and digestive gland, fish tissues, and land plants. These specimens were from the posttest collections, except for one alga that was collected before the Mike test. Little selective absorption of isotopes by these speciesso soon after the shot is observed, UNCLASS21ED,