In an attempt to unravel the effects of these radioelements, separate groups of young adult beagles were injected with Ra226, Ra228, and Th228 at this laboratory, and the metabolism and effects of these bone-seeking radio-elements and their daughters are under study. Thoron, a chemically inert gas, lies in the thorium decay series. The decay from mesothorium (Ra228) to thoron (Em220) is as follows: 6.7 yr 6.1 hr 1.9 yr 3.6 days (0 IRa~1 AAC22S IThI R }