gz THE POPULAR SCIENCE MONTHLY. 



2. The simj)le 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 pre- 

 sented 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 hypothe- 

 ses 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 con- 

 verted into a sensation. Let any one of these agents become incapaci- 

 tated, 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 con- 

 dition 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 convert- 

 ing power of the cerebral center, may be but slightly deranged or to- 

 tally deficient for some color or colors, and so the phenomena presented 

 by two cases falling under the same category would be very different; 



