17 nonexposed animals (increasing with age) but have been found in significantly greater numbers in mice exposed to even very low doses of radiation.?° * Methods Slit-lamp microscopic examination after iris dilatation with tropicamide 0.5% (Mydriacyl) was made of people within the several exposure groups Figure 17. Photographs ofthe optic lens taken through the slit-lamp microscope at 312 magnification and enlarged 24 x. Lens flecks are visible in and to theright of the lighesarc which lies at the left in each photograph, created by impingement of the lamp beam on the lens posterior capsule. Left: Mouse, nonirradiated, one year old. Right: Human,a 39-year-old Marshall Island female exposed to 175 rads offallout radiation 15 years previously. as follows: 175 rads (midline gammadose im air), 41 persons; 70 rads, 10 persons; 14 rads, 15 per- sons; nonexposed, 80 persons. The observer was unawareof the group to which each individual belonged until after the examinations. First a brief general inspection (at a magnification of 200 or 312 x) was made of the cornea, aqueous humor, lens, and anterior vitreous humor. Representative photographswere taken, usu....v at 312 x. Finally counts were made of minute discrete opacities (flecks) falling, wi .2,5-mm-diantetey’circle projected into the viewed aSeidbyatt ocular Counts weremade withirr vor andy subcapsular:regions ofcaeheder | locationabout one--half lenetedius pel ova midline. Thisloca- tion was selec ‘Fhintitae the-cgeneal light reflex as the nagpyait-lamp beam was swept adibss the counting. region, “Axial traverse of the focus duringcounti gave dapth to the couritifigarea, effectively creating‘acylinders of25-mm diameter and extending betweenthe lenscapsule and léns nucleus. - 74S OF Eight examinationswetbunsatistactéry betause be of advanced age cataracts, lens extractions, or corneal defects. we he os. Figure 18. Electran micrograph of optic lens fibers of a 21-week-old mouse exposed to 3000 rads of Co gamma rays at 6 weeks of age. The fibers are seen in cross section, and a defective fiber lies near the centerof the field. (From H.A. Johnson, Acta Iberica Radtol. Cancerol. 19: 247-54, 1964).