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Color-blindness appears to have attracted scientific attention for the first time when Dalton in 1794 described his own case. Consequently it was known for years as Daltonism, and many explanations have been advanced to account for it. The defect is an inability to distinguish certain differences of color, the colors most often confused being red and green, tho failure to discriminate between other hues occurs occasionally.

Brewster and Wartmann suggest as a cause of this inability an unresponsiveness to stimuli on the part of the nerve-fibers of communication; Laycock asserts that the imperfect action of the optic nerve results in a cerebral deficiency. Goubert says, "La seule cause vraiment connue de l'achromatopsie est l'hérédité, l'hérédité, comme Szokalski l'a montré, a lieu par les femmes, par les descendances féminines. Elles en reçoivent le germe de leur père et le transmettent à leur fils. Elles restent indemnes.” But he frankly confesses his ignorance of the origin of the defect, of its mysterious preference for his sex; asserting in his interesting treatise De l'Achromatopsie, ou Cécité des Couleurs that it is “

une anomalie du sens de la vue, congénitale, permanente, et jusqu'ici incurable,” and insisting “sur le mot congénital et sur l'absence des lesions matérielles,” a view of the subject with which Dr. Jeffries agrees.

Jeffries says in his report to the School Board of Boston, “Color-blindness is not curable by any known methods, and the color-sense does not alter thru life,” tho he adduces no proofs of the latter statement. He also, like other writers upon this subject, remarks the extraordinary rarity of the defect in women. “It has been supposed, and even claimed, that exemption on the part of females from color-blindness was due to their

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familiarity with colored objects and materials. This will not, of course, hold with reference to the individual, for the colorsense cannot be changed by practice with colors. Whether generations of color-education have caused this sexual difference is a point to be remembered, as, if sustained, it proves we may begin to eliminate color-blindness from future generations of boys by teaching and practicing their ancestors. It must be remembered that our community and our school children are not different from others. Wherever in the civilized world examinations similar to my own have been carried out by competent observers, the same facts as to colorblindness and ignorance of color-names and their have been found appertaining to males.” He thus assumes, as do others who have tested the color-sense of children, an inherent and congenital incapacity on the part of the present generation of boys to train by practice their colorperceptions, an assumption which, I hope to prove, is not upheld by results where this practice has been systematically given.

Dr. Jefferies examined, some years ago, 27,927 school children in Boston, at a time when no regular color-training was part of the school work. Among the 14,469 boys and young men he found 608 color-blind, or 4.2 per cent. This average also held good of the male students in the Baltimore City College, who were afterward tested by him. Of the 13,458 girls and young women examined by him in Boston he found but 9 color-blind, a proportion of .6 of one per cent. He recommended most earnestly that color be systematically studied, presumably in the interest of future generations of boys, profiting by the slow processes of heredity, since he maintained that “the color-sense does not alter thru life."

Wartmann found 4 men in every 100 color-blind; Kelland, 3 in every 150; Seebeck, 5 in every 40; Prevost 1 in 20. Wilson found the proportion of the color-blind among Edinburgh University students i in 30, but among the soldiers of the garrison, I in every 17, and asserts that the defect is always commoner among the untrained. But all declare that color-blindness is general enough to constitute a real danger under many conditions, and is, under all conditions, a serious

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drawback to the usefulness and enjoyment of those unlucky enough to be thus afflicted.

Virchow,. in addressing the International Medical Congress at Amsterdam, some years ago, asserted that savage races have no names for many colors and no power of discriminating between them. He had himself tested the truth of this with Nubians and Laplanders, and was inclined to think that colors must be learned. Magnus declares that the power of distinguishing color has increased among civilized peoples since Homer's day, as the great poet's use of color-adjectives will prove. However that may be, it would be an interesting experiment to undertake to show, from their use of descriptive terms of all sorts, the possession by our modern poets of exceptionally keen sense-perceptions.

The Ophthalmological Society of England has conducted examinations for color-blindness in 18,088 cases, finding it present in 4.7 per cent. of the men and in only .4 of one per cent. of the women. Cohn, Magnus, and Pfüger in Germany tested school children, finding an appreciable percentage of them color-blind. Favre, who examined the children in the Lyons schools, believed that congenital color-blindness might be cured by the exercise of the chromatic sense, but his tests were by the unreliable “Méthode d'appellation ” employed by Preyer, instead of the “ Méthode de reconnaissance,” which is the only manner in which the absence of color-discrimination may infallibly be detected.

It does not appear to have occurred to any of these authorities that the color-sense is one thing, and the color-perception quite another, tho Dr. Thompson, who conducted the examinations for the railways of the State of Pennsylvania, uses the significant expression “color-ignorance," and Dr. Jeffries says “Dullness of comprehension and dullness of perception will almost invariably simulate color-blindness.” If he had said that dullness of perception was color-blindness, psychologically, he would have clearly set forth the truth concerning this mysterious and much-discussed problem, it

may be,

Most writers, following Helmholtz, have assumed a triple mechanism in the eye which receives, registers, and transmits

to the brain the three primary sensations upon which our colorperceptions are based. The three fundamental impressions are assumed to be those of violet, green, and red, and when these are present, the color-sense is considered normal and the individual is said to possess “trichroic vision.”

“trichroic vision.” When one of the basic components of the color-sense is lacking, the vision is called "dichroic." That constitutes the defect known as color-blindness. This triple mechanism in the eye and its nerve-connections has never been shown to actually exist, and appears to be still a hypothesis awaiting proof. As Ladd points out, it does not explain color-blindness. Hering asserts that six and not three fundamental colors must be postulated, and Wundt insists upon a difference in the processes and not in the retina itself.

But all ignore the purely psychic factor of recognition, which is not a function of the sensory apparatus, but of the brain itself. Dr. Edridge-Green, in his recent work entitled Color-blindness and color perception, admits this, but fails to follow it out to its logical conclusion. He says the eye may be normal in every respect, the communication perfect between the sense-organ and what he terms “the perceptive center” in the brain, the entire sensory mechanism complete in each minutest detail, and yet if the “perceptive center” does not properly perform its task, the mind takes no cognizance of impressions duly received and transmitted to it by the peripheral system. He argues that color-perception is, in its essence, “a perception of difference," in other words a recognition of the fact that one color is not another color.

But the perceiving of differences is the work of the higher nervous centers, and is, in its perfection, the result of the careful training of these centers.

Herschel, also, ascribed color-blindness to a cerebral inability to discriminate between colors, but, so far as known, made no attempt to account for this inability. Dr. Goubert, in the treatise already quoted from, says that color-blindness does not belong to the realm of pathology, since there are no lesions causing it. But it does not seem to have occurred to any of these writers that it belongs to the realm of psychology. What are perceptions but the Besinnungs-Stoff with which all

our mental science deals, the fundamental psychic facts? To cite two pertinent passages from Ladd's Physiological psychology:

A true theory of the nature and growth of that knowledge of things which comes thru the senses must always be distinctively psychological. For all the factors built, as it were, into the products which we call ' perceptions' are mental; as we have already seen, these factors are sensations and sensation-complexes.” And again: “ Perception is then, and we can scarcely repeat or emphasize the declaration too much, a mental achievenment."

If then the eye is admittedly normal in cases of color-blindness, and there are no discoverable brain-lesions, the defect is, in all probability, a mental one, a mere lack of the power of discrimination, due to deficient training. It surely would not be reasonable to say with Goubert that we must assign it to “Une cause prédisposante bien établie, le sexe masculin," when all men are not color-blind.

But if color-blindness should prove to be due to a mere absence of training in early youth while the senses are most keenly impressionable, is it not possible to prevent this weakness by giving a systematic culture to the color-sense in childhood? And if it can be shown that boys, so trained while very young, discriminate and appreciate color as intelligently as girls, what becomes of the assertion that color-blindness is virtually a masculine monopoly and is transmitted by inheritance? Is not the inheritance of a defect inexplicable for which no reason, anatomical, pathological, or physiological has ever been discovered?

One hundred men in every two thousand (striking an average between Wilson's figures and Holmgren's) are colorblind, markedly so. The imperfection is rarely discovered by the individual himself, and undoubtedly many with defective color-perceptions live out their lives without becoming aware of all the beauty and glory hidden from them. In most of the cases reported, circumstances alone have led to the discovery of this absence of normal color-recognition, and the governmental tests now instituted in many services have occasioned disagreeable surprises to many unfortunate candi

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