127. Color-blindness. Holmgren's method. Spread the worsteds on a white cloth in good
daylight. Pick out a light green (i.e., a little saturated green) that leans neither toward the blue
nor the yellow; lay it by itself and require the person to be tested to pick out and lay beside it all
other skeins that are colored like it, not confining himself, however, to exact matches, but taking
somewhat darker and lighter shades also, so long as the difference is only in brightness and
not in color-tone. Do not tell him to pick out "the greens" nor require him to use or understand
color words in any way; simply require the sorting. If he makes errors, putting grays, light
browns, salmons or straws[3] with the green, he is color-blind; if he hesitates over the
erroneous colors and has considerable difficulty his color-vision is probably defective, but in a
less degree. If the experimentee makes errors, try him further to discover whether he is red-
blind or green-blind by asking him to select the colors, including darker and lighter shades, that
resemble a purple (near magenta) skein. If he is red-blind, he will err by selecting blues or
violets, or both; if he is green-blind, he will select green or gray, or both, or if he chooses any
blues and violets, they will be the brightest shades. It he makes no errors in this case after
having made them in the previous case, his color-blindness is incomplete. Violet blindness is
rare. Complete certainty in the use of even such a simple method as this is not to be expected
without a full study of the method and experience in its application.
On color-blindness and methods of testing for it cf. Helmholtz: Op. cit. G
2
357 372[sic]. 456-
462; G
1
294-300, 847-848; F. 388-400. Jeffries: Color blindness, its dangers and its detection,
Boston. 1879 (this work contains a seventeen-page bibliography on color-blindness and kindred
topics); also an article on Color-blindness in the Reference Handbook of the Medical Sciences,
New York, 1886 II, 241. Rayleigh and others: Report of the Royal Society's Committee on
Colour Vision. Proc. Royal Soc., LI, no. 311, July 19, 1992. Hering: Zur Diagnostik des
Farbenblindheit, Archiv für Ophthamologie, XXXVI, 1890, Heft I, 217-233; also Die
Untersuchung einseitiger Störungen des Farbensinnes mittels binocularer Farbenleichungen.
Archiv f. Ophtal., XXXVI, 1890, H. 3, 1-23. See also a [p. 397] paper by Hess in the same
place, pp. 24-36. Kirchmann: Beiträge zur Kenntniss der Farbenblindheit. Wundt's Philos.
Studien. VIII, 1892, Heft 2 i. 3; Helmholtz, Hering, Kirschmann and others give exact methods
for determining the particular colors that are lacking. On differences in the apparent extent of
the spectrum in different observers, see Morgan: Animal Life and Intelligence. pp. 280-283.
128. Vision with the peripheral portions of the retina. a. Campimetry. Color-blindness is normal
on the peripheral portion of the retina. At the very centre the pigment of the yellow spot itself
interferes somewhat with the correct perception of mixed colors containing blue (cf. Ex. 110). In
a zone immediately surrounding this all colors can be recognized. Outside of this again is a
zone in which blue and yellow alone can be distinguished, and at the outermost parts not even
these, all colors appearing black, white, or gray. The zones are of course not sharply bounded,
but blend into one another, their limits depending on the intensity and area of the colors used.
a.[sic] With the campimetrical apparatus at hand, find at what angles from the centre of vision
on the vertical and horizontal meridians of the eye the four principal colors, red, yellow, green
and blue can be recognized; try also for white. Keep the eye steadily fixed on the fixation mark
of the instrument and have an assistant slide the color (say a bit of colored paper 5 mm. square
pasted near the end of a strip of black cardboard an inch wide) slowly into the field from the
outside. It will be well to move the paper slowly to and fro at right angles to the meridian on
which the test is made, so as to avoid retinal fatigue. Take a record of the point at which the
color can first be seen with certainty. Repeat several times and average the results. The size of
the colored spot shown should be constant for the different colors, and the background
(preferably black) against which the colors are seen should remain the same in all the
experiments. b. Repeat the tests with a colored square 10 mm. on a side, and notice the earlier
recognition of its color as it approaches from the periphery. c. Try bringing slowly into the field
(best from the nasal side) bits of paper of various color, especially violet purple, orange,
greenish yellow and greenish blue; or better, hold the bit of paper somewhat on the nasal side
of the field and turn the eye slowly toward it, beginning at a considerable angle from it. If the
paper is held before a background containing a line along which the eye can approach the
paper, the eye will be assisted in making its approach gradual. Observe that on the outer parts
of the retina these colors first get their yellow or blue constituents, and only later the red or
green, and appear in their true color. If the range of choice is sufficiently large it may be