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 biological samples: gland, plankton, algae, fish tissues and land plants. octopus gill and digestive These specimens were from the post test collections except for one alga that was collected before the Mike test. Little selective absorption of isotopes by these species so soon after the shot is observed except for concentration of zirconium in an octopus gill and of rare earths by plankton and by a surgeon fish and a butterfly fish. Results of these analyses are shown in Table 18. Method Used. Twenty to fifty-gram portions of sand or soil samples were ashed at 700°C to destroy organic matter and the ash dissolved in dilute nitric acid. Filtering the solutions and counting the filters showed that solution of the active material was complete. Biological samples were also ashed and dissolved in dilute nitric acid. Filtering the solutions and counting the filtersfor these samples showed that in most cases the small insoluble residue contained less than 10 percent of the activity of the sample. Duplicate portions of the filtrates were taken and analyzed by the following methods. Rare earths and zirconium were separated as hydroxides by precipitation with ammonium hydroxide. The resulting precipi- tate was dissolved in nitric acid and rare earths separated - 79 -