material on May 22 and is being continued with the latest counts having been made on February 19, 1949. The material used in this study of activity decay is listed in Table II. The betaezamma counts expressed as counts per minute per gram of wet tissue are recorded in Table III with the essential data plotted in Figure l. The data show a very rapid decay of the enercy from mid~'fay to mid-September. From September to mid-February the counts o2 all the samples continued to decrease but at a mich slower rate. Fitting a straight line to the last three points of the curve i.e. for November 27, January 1 and February 19, the half-life period ig approximately 180 day8e The slope of the curves at the beginning and at the end tempts one to postulate that the predominant active materials may ve vae4 and Ca49,