The time of greatest sensitivity to radiation is during the period of organogenesis in the first twelve weeks of human foetal development. Irradiation of the adult can cause life shortening or increased incidence of leukemia. The last chapter is concerned with the basis and origin of radiation protection standards, the hazards of nuclear power plants, high altitude supersonic aerospace travel, civil defense, and finally medical irradiation and public health. Written as a series of four lectures, this book will be useful for instruction and as a reference book for physicians. It can be recommended as a straightforward text in which the important aspects of the subject are picked out of a vast literature and presented in an informative way.