26 pigmentation persisted for several years before it finally disappeared. These pigmented streaks are not to be confused with conjunctival and corneal pigmentation of genetic origin noted in some of these people, whichis in the superficial epithelium and is permanent. Pterygia and pingueculae. During the early surveys the incidence of pterygia and pingueculae was thought to be greater in the exposed Rongelap people than in the unexposed comparison population. However, as the latter group has increased, this no longer appears to be the case (see Table 14). Opacities of the lens. Opacities of the lens have been a common finding in the Marshallese (see Table 14). They are scored in order of decreasing size as cataracts (arbitrarily considered asa lens opacity impairing visual acuity by > 20/30), lens opacities, polychromatic sheens, and flecks. Special microscopic examinations for lens fiecks were madein 1969.18 Irradiation ofthe lens in sufficient dosages may result in a spectrum of opacities ranging from polychromatic sheensto full-blown cataracts,35-38 Only in the early stages of cataract formation can changes characteristic of radiation generally be recognized; more maturecataracts dueto radiation usuallycannot be differentiated from those due to aging or disease. The developmentoflens opacities due to radiation depends on the characteristics of the radiation, the age of the individual at exposure, and the interval after irradiation. Neutrons are known to be several times as cata- ractogenic as gammaor beta rays and played an important role in cataract development in the Japanese exposed to the atomic bombs andalso in cyclotron workers.37-39 In the Marshallese only gamma radiation need be considered because no neutrons were involved in the fallout and the beta radiation did not havesufficient energy to impart a significant dose to the lens. The gamma radiation had a fairly energetic spectrum (100 to 1500 keV). The 175-rad dose was delivered ata decreasing rate over the two days of exposure. The minimum cataractogenic dose of x rays or gamma rays is considered to be ~ 200 rads and the dose to produce progressive lesions, ~500 rads.4° The latent period averages about 2 to 3 years. With larger doses the latent period may be shorter, and with lower doses it may be 28 years. The smallest lens opacities observed withslitlamp microscopy were lens flecks, which are thoughtto be defects in single lens fibers. These discrete opacities were at most only a few microns in size and could in no way impair vision. The numberof flecks increased with agein all groups, but they developed more rapidly in adolescentfe- males.!3* A higher score in females aged 13 to 20 at exposure may havebeen related to the radiation. The higher incidenceof flecks in adolescent females was thought to be associated with their high estrogen levels. Other lens opacities observed in the exposed Marshallese did notfit the descriptions of radiation-induced types and weresimilar to those seen in the unexposed population. The absenceofradiation-induced cataracts is not unexpected, since the dose to the Marshallese was below the mini- mum dose of x rays or gamma rays needed. The lapse of 20 years is well beyond the usual latent period andit seems unlikely that any such lesions will develop. All the cataracts seen have been of the senile or pre-senile type and no juvenile cataracts have been noted. Possible correlation with diabetes is discussed in Section III. G. 6. Theslightly higher. incidence of cataracts in the exposed Rongelap people over the years may be related to a slight preponderance of older people in the exposed population. Polychromatic sheens, yellowish or “beaten brass’’ to blue-green in color, were noted in some Marshallese, both exposed and nonexposed. These were not associated with any lenticular opacities characteristic of radiation exposure. F. GROWTH AND DEVELOPMENT STUDIES OF EXPOSED CHILDREN 1. Data Taken During each medical survey of the Marshallese people, systematic pediatric examinations have been conducted on subjects under the chronological age of 20 years (see Table 15) with the exception of adolescent girls who were pregnant or who had hadbabies. Thestudies consisted of a brief interval history, routine physical examination,palpation of the thyroid gland, and assessment of growth and development. The growth status of the children exposed to fallout has been followed regularly since theinitial examination. From 1954 to 1958 the growth data consisted of routine measurementsof stature and weight. In 1959, roentgenographic evaluation of "These studies were done by Dr. J. Bateman, BNL.