The principles governing the effect of radiation on tumors in general apply with equal force to tumors within the abdomen. The only differences between tumors involving an abdominal organ or structure, and tumors arising elsewhere in the body, are such as may be due to differences in type and degree of specialization, and in anatomic, chemical and other metabolic relationships, including the distribution and supply of tissue fluids. The term "selective," frequently used to describe certain qualitative characteristics of roentgen or radium rays, is a misnomer, because radiations do not possess true selective power. Any differential action exerted by rays of a given type depends on the cellular sensitiveness of the tissues exposed. For instance, the pronounced and rapid destruction of the spermatogonia of the testes and of the circulating lymphocytes under a given dose of radiation is in striking contrast with the failure of a like dose to produce