re ORS row ws a Se toe -49Discussion The physiological roles of manganese, iron, cobalt, and gine in plants and animals are not completely understood. How- ever, these elements participate in many enzyme reactions and along with other elements have been conclusively demonstrated to be nutritionally essential to, and incorporated into, higher animals including humans (Underwood, 1956). In the present work, cetailed studies have been done on clam kidney and fish livers. Although the accumulation of the non-fission products is a process common to both animals, the concentration patterns for the different isotopes are not the same. These differences are to be expected between various phyla, and even between species within one phyla in which diffefent metabolic patterns or food habits ccecur, In the fish livers zn©> amounted to 35-58% of the total activity but in the clam kidney this lsotope was not present. On the other hand, the absolute levels of radioactive iron, cobalt, and manganese were much higher in the clam kidney than in the fish livers. The presence of large amounts of heavy metals in the clam kidney is in agreement with the observations of members of this Laboratory that the clam kidney has a remarkably high specific gravity in comparison to soft tissues of other animals. This high specific gravity is reflected in the relation of ashweight to wet weight in the present experiments. In the clam kidney the ash fraction accounted for 13% of the wet weight, but in fish an livers the ash accounted for only 2.6-2.9% of the wet weight. '* . re