Acknowledgements It is a pleasure to take this occasion to thank the personnel of the Laboratory of Radiation Biology and the faculty of the College of Pisheries of the whose efforts have provided support, University of Washington stimulation and encourage- ment in this work. I am particularly indebted to Dr. A. D. Welander for his counsel and guidance throughout the entire period in which this work was undertaken, and to Dr. Lauren R. Donaldson for the allocation of funds, travel, laboratory equipment and space, and instrument time under A.E.C. Contract No. AT(45-1)1385, without which this work could not have been attempted. Especial thanks are due to Dr. Prank G. Lowman who first stimulated my interest in the role of transition elements in marine biota, and who taught me the techniques of gamma spec- trometry. I am grateful to Dr. Diptiman Chakravarti for his assist- ance in working out the chemical techniques for the separation and determination of stable zinc employed in this work. To Dr. A. M. Dollar I am indebted for many stimulating discussions which proved invaluable in developing my understanding of many of the physico-chemical and biochemical aspects of JO

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