A text-book of physiology for medical students and physicians . means of the pe-rimeter (see p. 335). It will be found to vary with each individual,so much so that it is possible that a test of this character might beused for the identification of individuals. Exceptionally it is foundthat the entire retina possesses a nearly normal color sense. Usu-ally for the colors red, green, and blue, the blue has the most exten-sive field and the green the least, as is indicated in the perimeterchart given in Fig. 150. If the green chosen is blue green (490 )—that is, the complementary of the red—i
A text-book of physiology for medical students and physicians . means of the pe-rimeter (see p. 335). It will be found to vary with each individual,so much so that it is possible that a test of this character might beused for the identification of individuals. Exceptionally it is foundthat the entire retina possesses a nearly normal color sense. Usu-ally for the colors red, green, and blue, the blue has the most exten-sive field and the green the least, as is indicated in the perimeterchart given in Fig. 150. If the green chosen is blue green (490 )—that is, the complementary of the red—it is stated that their fieldsare co-extensive, t From this standpoint the retina presents three * Grunert, Archiv fur Ophthalmologic, 56, 132, Baird, The Color Sensitivity of the Peripheral Retina, Carnegie Pub-lication, No. 29, 1905. 352 THE SPECIAL SENSES. concentric zones: an extreme peripheral zone devoid of color vis-ion, an intermediate zone in which yellow and blue are perceived,and a central zone sensitive to red and green.* The outlines of. ** m S on ^ Fig. 150.—Perimeter chart indicating the average fields of vision for blu->, red, andgreen compared with white (gray). Right eye: The outlines of the color fields are repre-sented as smooth since the chart is an average from many determinations. As a matter offact, in each individual the outline is highly irregular. Normally green (bright green) is thesmallest field, green objects outside the limit appearing yellow and farther out colorless(gray). the different fields usually show many irregularities, and in somecases it will be found that bright green is perceived over a larger areathan the red. The fields are not identical in the two eyes, and ineach eye it is, as a rule, more extensive upon the nasal thanupon the temporal side of the retina. In the red-green blind theperipheral fields of color vision, judged by the individuals ownstandards, may be markedly constricted as compared with the nor-mal retin
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