ON ACCIDENTAL OR SUBJECTIVE COLORS. 253 



ing colors wouM seem, therefore, to predominate in women. Gall asserts that 

 the organ of color is more developed in woman than in man. 



Influence of age and parentage. — Daltonism dates ordinarily from birth. It 

 is often hereditary. It sometimes affects one, two, or more members of a family, 

 while the others remain exempt. It is remarkable that the transmission of 

 daltonism takes place rather throngh females than males, although females, as 

 we have seen, are themselves very rarely subject to the infirmity. M. Cunier, 

 however, has recently ascertained a case of hereditary daltonism in five con- 

 secutive generations, and always in females, who were alone affected. 



Explanation of Daltonism. — Some persons will see nothing in this affection 

 but a defect of intelligence or perturbation of the functions of the brain ; others 

 assume an abnormal coloration of certain parts of the eye which modifies the 

 true colors; others, again, think that the cause should be sought in the sensibility, 

 more or less great, not only of tlie retina in general, but specially of the different 

 nervous fibres which vibrate in unison with such or such a color, or which are 

 impressible by such or such a tint. The first opinion we shall not stop to 

 refute. The second was held by Dalton, who concluded from his personal ob- 

 servation that the humors of his own eyes and of those of his students were 

 tinged with blue. He ascribed this peculiar coloring to the vitreous humor; but 

 the researches of anatomists have never brought such coloration to light. More- 

 over there are observed facts which would be very imperfectly explained on this 

 hypothesis. Persons who habitually use blue glasses are not thereby exposed 

 to a confusion of colors. Goeihe, on the other hand, conceived that daltoniaus 

 were insensible to blue, but saw in its place a pale purple or rose color. This 

 view, liowever, is evidently inconsistent with facts. 



From the sum of the observations heretofore made, two conclusions, we think, 

 may be drawn : 1st, that daltonism never extends to yellow, a color which all 

 eyes are capable of seeing ; 2d, that the sensations of two complementary colors 

 are inseparable, in the meaning that the eye is either sensible or insensible to 

 both at the same time. The eye which perceives blue perceives also an orange 

 color. The eye which does not discern red is incapable also of distinguishing 

 green; these two colors it confounds. The above conclusions comprise in them- 

 selves all the phenomena of daltonism. They are, moreover, a necessary con- 

 sequence of the theories of MM. Melloni and Plateau, and might be enunciated 

 a priori, even previous to their verification as a consequence of fxcts. But 

 these conclusions being once admitted, it becomes evident that the cause and 

 explanation of daltonism is to be sought in an anomalous insensibility of the 

 eye, which deprives it of the faculty of vibrating in unison with such or such a 

 luminous ray. 



We shall not insist further on this point. Let us conclude by indicating the 

 very simple means by which the elder Seebeck succeeded in rectifying to a 

 certain extent the error committed by daltoniaus in the appreciation of colors. 

 This means consists in the use of glasses, or more generally of colored mediums. 

 Suppose, for example, that an eye confounds green with red. It will evidently 

 suffice to furnish this eye with a red glass in order that the difference between 

 the two colors shall be distinctly perceived. The surprise of a daltonian is 

 inexpressible when thus enabled to discover the errors which he is constantly 

 making. By this means, however, only mistakes relative to the nature of colors 

 are remedied. Tne inability to distinguish between shades of the same tint will, 

 in general, still subsist. 



