Page:Popular Science Monthly Volume 21.djvu/100

92  2. The simple colors are not complementary, as Hering asserts; blue-green, and not green, is the complementary color of red, and violet-blue, and not blue, is the complementary color of yellow. The simple colors can not, therefore, be considered as antagonistic. 3. The white, which comes from the union of two of Hering's antagonistic colors, is not the result of subtraction, but of addition, as is shown when, with a double spectroscope, a saturated violet being made to cover a yellow, a white is produced which is manifestly more intense than the yellow, while another yellow of the same intensity as the violet added to the yellow does not produce a yellow intenser than the yellow resulting from the first experiment. 4. White is not a direct independent sensation; it is absent in the spectrum where, in red-blindness or violet-blindness, the specific color is absent (Donders).

From the foregoing, and from a study of the phenomena as presented by a number of color-blind persons, two important facts are forced upon the unbiased observer: 1. That we have not yet arrived at any fixed laws governing the phenomena; that all cases can not be classed as distinctly red, green, or violet blindness, though it seems probable that all might be classed under the heads of red-green and blue-yellow blindness. 2. That neither of the two prominent hypotheses fills the demands of an acceptable theory, inasmuch as both fail to account consistently for all the phenomena.

It seems to us that, in the consideration of the subject of color-blindness hitherto, too much stress has been laid on the part which the retina plays in color-perception. There are three distinct agents at work in the perception of color. The impression is first made on the retina; this is carried thence by means of the optic nerve to the center in the brain which presides over the function of vision, and it is there converted into a sensation. Let any one of these agents become incapacitated, from any cause, for properly carrying on its function, and there must be a perversion or absence of sensation. In certain affections of the retina and optic nerve we have instances of color-blindness from deranged or abolished functional activity of the first two agents, and in some forms of toxic action, particularly alcoholic poisoning, we have in all probability examples of the cerebral form of color-blindness. The supposed color-fibers or color-substances may be in a perfect condition and acted upon in a perfectly normal manner by light, but the optic nerve may be incapacitated by some change in its molecular structure from carrying all of the impressions correctly to the brain-center, and, even should all the separate impressions arrive there, the cerebral center itself may not be in condition to convert them into the proper sensation. The conducting power of the nerve, or the converting power of the cerebral center, may be but slightly deranged or totally deficient for some color or colors, and so the phenomena presented by two cases falling under the same category would be very different;