PROBLEM OF COLOR VISION—DANE. 619 
green-yellow, and then the yellow-red, which however are still per- 
ceived as colorless light. Thus a gray molecule like that of Mrs. 
Franklin’s first stage is constructed. It occurs in the color blind 
peripheral cones. The formation of color-reacting groupings in 
the partly sensitized gray molecule leads, according to Schenck, to 
those forms of human vision in which the red end of the spectrum is 
shortened. 
Observations upon the color perception of young children do 
not support these developmental theories. Holden and Bosse tested 
two hundred children by placing before them square pieces of col- 
ored paper attached to a gray background of similar brightness. 
If the child made an effort to grasp the square, its color must have 
been perceived. It was found that the average child would react 
to all colors by the tenth month, the red end of the spectrum causing 
response a little earlier than the violet end. When ribbons of six 
spectral colors were placed before children of from seven to twenty- 
four months, red was selected first; orange or yellow second and 
third; and green, blue, and violet last of all. Nagel’ showed his 
child of twenty-eight months each of the spectral colors in varying 
degrees of brightness, at the same time teaching him their names. 
Red and green were learned easily, but blue was acquired with greater 
difficulty than any other color, including violet. Green, violet, and 
red were preferred; black, yellow, white, gray, and blue had second- 
ary rank. Other experiments with the color perception of children 
have given different results. It is clear, however, that children are 
not known to pass from a color blind stage, through one of yellow- 
blue vision, to a discrimination of all the spectral colors. No race of 
men now exists in which any of the colors is unknown; and the notion 
derived from studying the color terms and references in ancient 
literature, that man in historic times had a deficient color sense, is 
not substantiated. It may be that, as in children, the red portion 
of the spectrum was preferred to the blue, but even this is not estab- 
lished. 
COLOR BLINDNESS. 
All the colors which are normally perceived may be produced by 
combinations of the spectral red, green, and blue. Normal vision 
is therefore trichromatic. Sometimes in trichromatic vision the red 
end of the spectrum is shortened; in other cases a mixture of red 
and green, which to normal persons appears pure yellow, may seem 
@Holden, W. A., and Bosse, K. K. The order of development of color 
perception and color preference in the child. Arch. of Ophth., 1900, vol. 29, 
pp. 261-277. 
> Nagel, W. A. Observations on the color sense of a child. Journ. of Comp. 
Neur., 1906, vol. 16, pp. 217-280. 
