known to adsorb trivalent rare earths rapidly in the particulate form from sea water’, and bismuth-207 probably would be adsorbed in a similar manner. A possible mode of production of this isotope is bismuth-209 (n-3n) bismuth-207. The D-T reaction would result in neutrons with sufficient energy to produce bismuth-207 by this method!. F. G. Lowman * R. F. PaLumMBo Laboratory of Radiation Biology, University of Washington, Seattle, Washington. “ Professor, Puerto Rico Nuclear Center, Colleve Station, Mayaguez, Puerto Rico. Sandell, EB, B.. Colorimetric Determination of Traces of Metals (Interscience, New York. 1959). ? Kimura, K., and Ishimori, T.. Second Intern. Conf. Peaceful Uses of Alomie Energy, 28, 151 (1958). *Chipman. W, A.. Abst. Prog. Ren.. List Pub., ele., U.S. Fish and Wildlife Serrice Radivisotope Lab., Beautort, N.C. (1956); Prog. Rep, US. ish and Wildlife Service, Pishery Radiobiat. Eab., eaufort, N.C. (1956). ‘Seeger, P. A., Nuclear Phys., 25, 1 (1961). Printed inGreat Britainby Fisher, Knight & Co,, Ltd., St. Albans.