cases to produce evidence of injury; hence, a higher threshold for cancer production than that for minimal damage from an acute dose. Skin cancer production shows little radiation time-intensity dependence and, like the genetic effect to be discussed later, the incidence is probably a linear function of total dose. The measures which may be taken to prevent beta burns of sufficient severity to reduce the efficiency of military or civilian populations are quite simple and effective. The cornified layer of skin covered with loose fitting clothing provides the minimm protection necessary to prevent serious injury to the living layers of the skin. Brennan and his co-workers have reported the following thick- nesses for standard items of Army apparel: Item Mgm/ m= Undershirt Shorts 17 12 Trousers 77 Shirt Field Jacket 2 186 O" x 0.6 Ao From beta range considerations, it can be shown that the above items of clothing can effectively protect against beta energies from O.1 mev to 0.6 mev. The protection afforded by ordinary clothing is easily augmented by wearing gloves and by frequent washing with soap and water when working in an area of fall-out or suspected contamination. The Genetic Problem. In considering the genetic problem due to local fall-out, the probability must be considered that "local" may involve an entire nation such as the United States in the event of an atomic war. For surface bursts, approximately 50% of the fall-out radiation has been accounted for locally. The radiation risk at early times after fall-out has begun is greater than at later times due to the decay characteristics of fission products. These two facts ind- cate that potentially at least the genetic problem due to total fallout may be primarily determined by the effects brought about in 89