(c) Algae. In order to evaluate the speck contamination of algae, autoradiographs of washed and unwashed specimens were made, Washing was done by scrubbing with a brush and detergent and was followed by rinsing with running tap water. Autoradiographs of an alga, Udotea, before and after washing, are shown in Fig. 4.17. Some of the radioactive spots were removed by washing, but most of them were not, showing that a major portion of the radioactivity is actually present within the aiga. The even distribution of radioactivity in the filaments of Lyngbya and in the ramuli of Bryopsis, shown in Fig. 4.17, indicate that speck contamination is of minor importance in these specimens. In one alga of the preshot collection (Fig. 4.17), adhering soil particles were responsible for numerous hot spots in the autoradiograph. The autoradiographic method has indicated the presence of both surface and absorbed contaminztion in the algae collected before and after Mike shot. The relative amount of speck contamination was high in some cases and low in others; however, a quantitative estimation cannot be made. (d) Dwertebrates, Among the invertebrates an outstanding example of spotty distribution of activity was the occurrence on a piece of coral of the genus Acropora, taken at Bogallua Nov. 8, 1952, of three highly radioactive nodules firmly attached and probably of foreign origin. The nodules did not appear to be part of the coral but were so well attached that, when one of them was removed for counting, it could not be separated from the coral without being broken. This unashed 1-mg hollow sphere yielded 100,000 d/m. It is possible either that these bodies were cysts produced by the coral itself for the purpose of walling off irritating highly radioactive particles or that they were rapidly growing neoplastic growths which had concentrated a great amountof radioactivity since the time of the blast (Fig. 4.18). Photographs and autoradiographs of Heliopora and of the above samples of Acroporacollected at Bogallua are shown in Fig. 4.18. The specific activity of the Acropora was 7,000,000 d/m/g and of the nodule 100,000,000 d/my,g, i.e., 100,000 d/m/mg. After the autoradiographs were made, another piece from the same sample of Heliopora was used in an attempt to complement the resuits with quantitative data. The thin outer layer, about 1 mm thick, the dense median portion corresponding to the least dense portion in the autoradiograph, and the rela- tively porous central portion were separated from one another and ashed for counting. The resulting specific activities were 3,400,000, 160,000, and 1,000,000 d/m/g, respectively. It seems likely that the radioactivity found in the median portion lined small cavities which are present in the skeleton rather than actually being incorporated in the coralline material. Infisha fairly even distribution of active material is seen in muscle, liver, gut, a more specks were in evidence in this tissue. In some fish a concentration of activity was noted in the gills (Figs. 4.19 and 4.20) or in the teeth (surgeonfish, Figs. 4.21 and 4.22). Carnivores and omnivores showedstriking differences in the amount within the budy cavity (Figs. 4.21 and 4.22). (@f) Land plants, Washing with running tap water removed 10 to 20 per cent of the activity on the land plants in most cases, although a much higher percentage of the speck contamination was removed by this method from the leaves of a grass collected at Engebi (Fig. 4.23). The remainder of the radioactivity was partly spotty and partly homogeneous in distributicn. The Spotty activity was probably due to material that was not washed from the external surfaces of the plants, and the homogeneousactivity was the result of dissolved radioactive material that had been actively absorbed and metabolized by the plant. In leaves radioactivity was highest in the veins, the conductors of absorbed materials throughout the leaves. 4.9.2 Other Surface Contamination The general problem of surface contamination from indirect sources is illustrated by specific examples, such as the contamination found on the carapace of a crab, on the shell of a clam, in the skin and gut of the sea cucumber, and on the outer surfaces of algae and land plants. 73 - ne oF _SCLASSIFED | we (e) Fish, and, to some extent, in bone. Most of the activity was in the gut and liver, as indicated by counts and autoradiographs. The activity is less evenly distributed on or in the skin in that