ACKNOWLEDGMENTS This report has been prepared by the staff of the Health and Safety Laboratory, AEC. Edward P. Hardy, Jr., and John H. Harley have been responsible for the editing of the material, under the direction of Dr. S. Allan Lough, Director of the Laboratory. The compilers of this summary appreciate the assistance given by workers in this field in making their data available. In particular, the following groups have allowed reproduction of their results: Dr. W. F. Libby and Dr. E. A. Martell, The University of Chicago; Dr. J. Laurence Kulp, Lamont Geological Observatory; Dr. N. G. Stewart, Dr. F. J. Bryant, and Dr. J. Rundo, Atomic Energy Research Es- tablishment (Harwell); Dr. W. E. Grummitt, Atomic Energy of Canada Limited; Dr. Wright Langham and Dr. E. C. Anderson, Los Alamos Scientific Laboratory; Dr. J. Terrill and Dr. Lloyd Setter, U. S. Public Health Service; Dr. Luther B. Lockart, Naval Research Laboratory; and Dr. Leo Marinelli and Dr. C. E. Miller, Argonne National Laboratory. The editors wish to acknowledge the assistance of Hal Hollister, Division of Biology and Medicine, AEC, in the preparation of the bibliographies and in obtaining reports for inclusion in this report. This report has been prepared and given limited distribution in four volumes designated as HASL-42, Parts A, B, C, and D.