C. Beta lesions of the skin, epilation Muitiple beta lesions of the skin, mainly on the areas of the body not covered by clothing, and spotty epilation associated with beta lesions of the scalp eppeared in many of the people beginning 12 ~ 14 days after exposure and continuing over the following few weeks. Most of the lesions were superficial and were characterized by thickening and pige mentation of the akin accompanied by mild itching and burning. Desquama- tion followed with healing and repigmentation over the next few weeks. Regrowth of hair began about 3 months after exposure with complete return of normal hair by 6 months. About 20% of the cases exhibited more severe lesions which ulcerated but, in all except one severe ear lesion, complete healing occurred within a few weeks. Microscopic changes were character- istic of radiation effects with the epidermis showing the greatest damage. About 14 cases continue to show residual changes at this time characterized by mild scarring and atrophy and varying degrees of decreased and, in some cases, increased pigmentation. In no case, either grossiy or microscopically, has any malignant or pre-malignant change been observed. D. Internal absorption of radioactive isotopes At present the accumulated evidence supports an assumption made initially that following contamination by fallout the radiation dose from external sources would be higher than that from internally deposited sources, Because, however, 30 relatively littie is known about the mechanisms and consequences of internal deposition of fission products, study of this phase of the problem was among the first of the studies undertaken in 1954 and has continued to be a part of subsequent re-examinations of the exposed population. A few short-lived radioisotopes, pt sr°?, and pal*0 | accounted for most of the ectivity found in urine specimens obtained during the first -12-