COLOR BLINDNESS

or ACHROATOPSIA, is characterized by inability to differentiate between certain colors or shades of colors. This is caused by defective structure either of certain brain cells in the visual regions or of the nerve endings, the rods and cones of the retina. Achroatopsia is now recognized as a heritable, sex-linked characteristic affecting about 3-4% of males and 1% of females, and is often accompanied by defective sight, usually hypermetropia. To color-blind persons, the spectrum is shortened, usually at the red end, which has the effect of making red appear as green, and green as red. There are three cla es of color-blindne : (1) that in which tiere is a light as well as a color lo . (2) that in which the perception of light is normal but the perception of color is defective. (3) that in which there is a defective perception of color owing to an abnormality of the central region (fovea) of the retina. A color blind person is nece arily barred from certain occupations which require a correct sense of color. Applicants for the Navy and merchant marine as well as locomotive engineers and motormen are carefully examined for these defects, since failure to recognize a colored signal may be the cause of a s ious accident,