42 137¢s characteristically seen in ruminants (Hood and Comar, 1953), probably relates to the kind and greater bulk of their diet (Davis, 1963). Cesium behaves in a manner that is phystological ly somewhat analogous to potassium. Hence, cesium is distributed throughout soft tissues, and can expose those tissues with beta and gamma frradiations. Unlike the bone- » seeking radfostrontium, however, retention is short (that is, elimination is rapid), with tissue exposure (and dose) declining with a half-period of about 2.5 to 5 months in people. Because 137Cs intake results in uniform exposure of al] tissues, its significance as a hazard to the most sensitive tissue must be balanced by its distribution and dilution into all tissues. Cesium-137, like tritium, which also is unifonaly distributed in the body, possesses the potential for genetic injury as well as carcinogenesis in sensitive tissues. Radiobiologic Effects Beginning in the 1960s, the long-term effects of 137Cs were studied in beagles at Argonne National Leburatory, a3 reviewed by the MCOP (1977). Sixty-five beagles in a lifetime study were given single intravenous infections of 157Cs with dosages ranging fran 1.65 to 4.3) mCi 137Cs/kg, among their age groups. Destruction of bone marrow resulted in 25 deaths within 2 months after injection. Cancers were the main cause of death of the 40 dogs that survived acute effects (up to 12 years post-injection), and accumulated fran 700 to 1609 rads. Cancers accounted for 20 deaths, and cancers were also found in ttssues of other dogs dying fram other causes. Neur of fbrosarcana, a tumor of the nerve sheath that is rere in dogs, was the most frequently occurring cancer, and was found tn A of the 49 dogs,