the gamma ratios of cesium-137 to potassium-40 in place of the cesium unit. Cesium units for Birgus muscle are given in Table 1 for compari- son with other published data on fallout given in the same units. However, since the potassium and cesium levels are both highly variable in Birgus muscle, there is some doubt as to the usefulness of the unit in this case. For example, the comparatively high value for cesium units of samples from Rongelap Island is due to the exceptionally low potassium of one of the samples content On the other hand, the high value for the March 1959 collection at Kabelle Island is due to high levels of cesium-137, while the potassium levels are about average. These differences are not surprising when the following facts are considered. Gross (1959) has reported that Coenobita, which has habits similar to those of Birgus, obtains blood salts from its food. From work in progress at this Laboratory it is known that Pandanus fruit, which form apart of the diet of Birgus, vary by as much asa factor of five in cesium-137 content and a factor of four in potassium content and that the range in potassium levels in soils on which Pandanus grows at Rongelap is 0.1 to 1.5 milliequivalents per 100 grams. Also, the extremes in the range of gross beta activity in the top inch of soil at a single island differ by more than a factor of ten Ona basis of the variability in cesium-137 and potassium levels found in the environment alone, might expect the high degree of variability found in Birgus. can one iP CAS . »ao™