Color blindness

“ It is more difficult to demonstrate whether a person sees colors correctly or not. Such glaring mistakes as those produced by color-blindness can be easily recognized, but faults produced by a diminished sensation of small differences in the shades of color can only be recognized as such by the fact that the majority of persons with normal vision declare them to be faults. Such, for instance, are deviations produced by an incorrect perception of pigments, which in painting makes itself felt by a constantly-recurring plus or minus of a single color in the whole picture. ”

“ Color blindness, when present, is usually most apparent in a failure to distinguish between red and green, these two widely differing colors seeming to produce the same impression upon the color-blind eye. The child will be just as likely to choose a red ball to match the green one in his hand as to select another red ball. But repeated tests should be made before accepting color blindness as a fact, since sometimes the brain can be educated to discriminate between red and green even when the impressions have not the normal degree of difference. ”

“ Partial color blindness is due to a defect of the retina which makes it unable to be affected by light waves producing red and green. A person with this defect confuses red and green. While only a small percentage of the population has this defect, it is nevertheless very important that those having it be detected. People having the defect should not be allowed to enter occupations in which the seeing of red and green is important. It was recently brought to the author’s attention that a partially color-blind man was selling stamps in a post office. ”

“ Color Blindness. The nerve fibers of the eye which carry the sensation of color to the brain are particularly sensitive to the primary colors—red, green, blue. Indeed, all color sensations are produced by the stimulation of three sets of nerves which are sensitive to the primary colors. If one sees purple, it is because the optic nerves sensitive to red and blue (purple equals red plus blue) have carried their separate messages to the brain, and the blending of the two distinct messages in the brain has given the sensation of purple. ”

“ When we know that only two females in every 1,000 among whites are color blind, it is not surprising that I did not find any examples among the Indian girls.
The usual tests for color blindness are the matching of wools; the common error the color blind falls into is matching a bright scarlet with a green. On one occasion, a color blind gentleman found fault with his wife for wearing, as he thought, a bright scarlet dress, when in point of fact she was wearing a bright green. ”

“ In the case of total color-blindness, we need only to assume that the nerve-fibers are in an abnormal condition, so that each set, instead of responding to only one sensation, responds equally to all. The result must necessarily be a total absence of color in the impressions received through the eye. In the case of a red-blind person, the nerves which ought to respond to red may either be paralyzed or they may be wanting altogether, and all other defects in color-vision may be explained upon the same principle. ”

“ They are probably few, however, who do not feel some stirrings when they look through the stained glass of a cathedral window or upon the red of Venetian glass, or who are entirely indifferent to the color of silk. The reason for emotional color-blindness is probably not a native incapacity to be affected, but rather a diversion of attention; color has come to be only a sign for the recognition and subsequent use of things, a signal for a practical or intellectual reaction. In our haste to recognize and use we fail to see, and give ourselves no time to be moved by mere seeing. ”

“ Purple made from this combination is inferior.
5 COLOR BLINDNESS Today, color-blindness is a serious difficulty in the way of a person earning a living. A generation or so ago, it was considered a matter of small importance. Many persons, suffering from the disease, went through life without knowing they were afflicted. The only persons, as a class, who were greatly affected by the problem were railroad men, who had to take tests for the distinction of colors. ”

“ The individual who is found to be green-blind by one method of examination is often found to be red-blind by another, and in some cases to have a shortening of the red end of the spectrum. Moreover, the red-blind can not unerringly pick out the greens, nor the green-blind the reds.
If, as we believe, a large number, perhaps a majority of the cases of congenital color-blindness are cerebral rather than retinal, and due more to a want of education of the color-sense than to any anatomical defect, a plan for the diminution or eradication of color-blindness would be by no means chimerical. ”

“ This defect but rarely assumes the form that would be termed absolute color-blindness, or want of any sensation of color. Where this form is perfectly developed there is generally a sharp, well-defined appreciation of differences between light and shade, or even between the finest grades of apparent brightness or intensity; but recognition of color is entirely wanting, there being no distinction whatever between different colors having the same degree of intensity. A curious fact might be noticed in this connection, that these defects are but rarely found in women. ”

“ A case of total color-blindness is very rare, but a few 95 are on record. When a child shows deficient color perception,34 a little care may save him much discomfort, and patient training may correct it. If he mismatches some hues, confuses their names, seems incapable of the finer distinctions of color, study to find the hues which he estimates well, and then help him to venture a little into that field where his perception is at fault. ”

“ Defects of vision in such cases on the part of any one employed may lead to fatal results. Color-blindness, by which is meant either an imperfect perception of colors, or an inability to recognize them at all, or to distinguish between colors, or between some of them, is a defect much more common than is generally supposed. Medical treatises of recognized merit on the subject represent, as the result of extended examinations, that a fraction over 4 per cent. of males are colorblind. ”

“ By the aid of this color system it is easy to understand an abnormality of our color sense which occurs rather frequently, so-called color blindness. It is found almost exclusively among men, three per cent of them being affected, whereas it is very rare among women, although it is inherited through woman. Instead of three dimensions, two are sufficient for the representation of the color sensations of such individuals: a plane which is placed through the points white, black, blue, and yellow. ”

“ THERE are some curious things in regard to the way in which the human mind is affected by colors as well as the human sight. We are all familiar with what is termed color-blindness, and the unexpected results that sometimes attend it; but color-sound is something which has received much less investigation. ”

“ The perception of color is very complicated, and not at all well understood. Persons who do not have the same color perception as most of us are called color-blind, and by learning some things about color-blindness we shall best get an idea of color perception itself. About four men in one hundred have defective color sense; the proportion in women is only about a tenth as great. ”

“ 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. ”

“ In one form there appears to be simply an imperfect or undeveloped sense of color, the power of distinguishing the different colors, though not wholly absent, being far below the normal. In the other form of the defect there is an entire inability to recognize one or more of the primary colors—that is, the blindness is complete so far as particular colors are concerned. ”

“ When a patient regards a black letter and believes it to be grey, yellow, brown, blue, or green, he is suffering from an illusion of color. This phenomenon differs from colorblindness. The color-blind person is unable to differentiate between different colors, usually blue and green, and his inability to do so is constant. The person suffering from an illusion of color does not see the false colors constantly or uniformly. ”

“ Next let us take the case of an intelligent person affected with colour blindness, but who is not yet aware of the fact. He has been taught from childhood that certain shades, some darker and some brighter, but all of neutral tint, and not really presenting to him colour at all, are to be called by various names—scarlet, crimson, pale red, dark red, bright red, dark green, dark purple, brown, and others. With all these he can only associate an idea of gray; nor can he possibly know that any one else sees more than he does. ”

“ Partial colour-blindness is, no doubt, the cause of the frequent disputes that we hear about the tints of certain objects; to say nothing of the glaring instances of bad taste in the arrangement of colour that are now-a-days so common. ”

“ The common form of defective color-vision is the inability to distinguish between red and green. As green lights mean safety, and red lights danger, on railroads, on shipboard, and elsewhere, it becomes of paramount importance that no one who is color-blind should be employed in such service. ”

“ It is singular that instances of colour-blindness are much more common amongst men than amongst women, for out of over five hundred cases there were only four in which females were the sufferers. It seems also that persons with grey eyes are more frequently colour-blind than those whose eyes are blue or brown. ”

“ In this way, by continual straining of the eye in search of a particular signal, especially at night, with no light beyond that of the glaring furnace of the engine—in itself detrimental to the eyes—it is quite possible that colour-blindness may be acquired, and that a man who was once perfectly able to distinguish the most delicate tints may become insensible to the effects of widely different colours. ”

“ Taking [Pg 158] the trichromic theory of three sensations for the normal-eyed person, it is evident that only the following classes of sensations are possible in the normal-eyed, the green colour-blind and the red colour-blind—
If we take as a type of colour-blindness the green colour-blind person, we see that every colour in the spectrum must be either pure red or violet, or else these colours mixed with more or less white light, since these two sensations when excited in certain proportions give the sensation of white. ”

“ There are, however, a large number of cases in which, though complete red- or green-blindness is wanting, there is no doubt that more than slight colour deficiency exists. For instance, in Fig. 23 we have the curve of luminosity of the spectrum as measured by a very acute scientific observer, and it is compared with that of normal colour vision. He certainly is not completely blind to any sensation. An inspection and comparison of the two curves will show that he is defective in the green sensation, although it is present to a large extent. The deficiency is obvious enough. ”

“ A lack of acuteness of vision would be expected from the small amount of light they perceive compared with normal vision. The fact that two of a family, not twins, possess exactly the same colour sense, and that their extinction curves are entirely different to those suffering from post-natal disease, but similar to those of normal vision, point to their colour blindness as falling in the same general category as that of the congenital type. ”

“ The cause of colour-blindness is completely unknown; philosophers and physiologists are still in the realms of hypothesis concerning this peculiar optical defect. As yet, the most careful observation has failed to detect any difference between the eyes of those who are colour-blind, and the eyes of ordinary persons, that could in any way account for this singular affection of the sense of sight. ”

“ Colour-blindness, inability, still unaccounted for, to distinguish between colours, and especially between red and green, more common among men than women; a serious disqualification for several occupations, such as those connected with the study of signals. ”

“ When no light enters the eye the sensation is of black, and it is worth while to note that so far as our sensations are concerned black is as much a color as white or any other, notwithstanding the fact that no light falls on the retina when the black sensation is being felt. Contrary to ordinary belief, blind persons who are blind because their eyes have been destroyed do not see black all the time ”

“ Colour-blindness is much more frequent than is generally supposed, for those who are afflicted with it are mostly ignorant of the defect, and frequently practise trades or professions in which perfect sensibility to the different hues of colour is quite indispensable. ”

“ With the spectrum test the red will require a greater dilution with white before it will be matched with a green, even if it can be matched at all. Measures of the luminosity at four or five positions in the spectrum, extending from near the extreme red to the blue, will give an unerring criterion of the kind and extent of colour blindness from which they are suffering. The existence of a neutral point in the spectrum is sufficient to indicate that their blindness is of a nature to be dangerous in certain occupations. ”