The Atlantic monthly 270, 1880
* Color-Blindness: Its Dangers and its Detection. By DR. B. JOY JEFFRIES. Boston: Houghton, Osgood & Co. 1879.Dr. Jeffries' treatise* deals with a subject which is interesting mainly from a technical point of view, most immediately concerning members of the medical profession and the administrators of railroads and steamship lines. The study of the singular defect of vision known as color-blindness is not, however, devoid of interest to the general public. The subject is very carefully and elaborately treated by Dr. Jeffries, and a perusal of his book cannot fail to afford much curious and valuable information.
Sunlight, as every one is aware, is composed of a mixture of primary colors which can be decomposed by passing through a glass prism. According to the Young-Helmholtz theory of color sense, these seven spectral colors can be reduced to three base colors, namely, red, green, and violet. Color-blindness consists in an inability to perceive rays of one of these base colors. Thus three main forms of color-blindness exist, aocording to the color of the rays which fail to excite the visual sense. In red-blindness, for instance, which is by far the most common form, the next being green-blindness, the red rays of the spectrum, whether pure or mixed with other rays, as in white light, are unperceived, being eliminated, as it were, from the visual impression experienced by the red-blind person. The remaining rays of the green and violet categories, including the blue and the yellow rays, are perceived and accurately differentiated from each other.
We must not, however, assume that the red-blind individual sees these other hues of the spectrum, or even pure white light, as they appear to a normal vision. The red rays to which he is insensible, though existing with their maximum purity and concentration in what we call the red part of the spectrum, also pervade, in varying degrees of intensity, all the other parts, and enter more or less into the composition of all the other hues. By the elimination of the red element, these other colors suffer an alteration which a person with normal vision finds it hard to imagine, but which must greatly affect their appearance. A pure white to a red-blind person is composed of a combination of the two other base colors which he is able to perceive, — a combination which to the normal sense would appear like a bluish-gray.
The nature and seat of the infirmity are unknown. It is almost invariably congenital and hereditary, though a few cases have been observed where a temporary color-blindness resulted from injury. It occurs almost exclusively in the male sex, one in about every twenty-five men being color-blind; whereas among females, only one in every nineteen hundred is similarly affected. Curiously enough, though women enjoy an almost absolute immunity from color-blindness, it is nevertheless through the mothers that the infirmity is transmitted to their sons. This unilateral inheritance, limited to the male offspring, although taking place through the mothers, is also known to occur in certain diseases (for instance, in hæmophilia and in pseudo-hypertrophic muscular paralysis).
Color-blindness is an infirmity which in many walks of life is attended by little or no apparent inconvenience. Though the outer world with one of the base colors and about thirty per cent. of the light omitted must present a strange appearance compared to what a person with a normal color sense sees, still many color-blind people never betray to others, nor even discover themselves, that their vision is defective. It is often a cause of startling surprise when the nature and extent of the deficiency is discovered. Dr. Jeffries gives an amusing account of the various mistakes, some of them quite comical, by which color blind individuals learn or reveal the imperfection of their vision. Dalton, from whose name the defect has sometimes been called Daltonism, was a Quaker, and as such wore only drabcolored clothes. But when he bad been made a doctor of civil laws at Oxford, and was presented at court, he not only felt no scruple at wearing the scarlet doctor's gown, but he subsequently wore it for several days in the street without being at all conscious of his conspicuous appearance. Professor Whewell asked him how the color of this scarlet gown looked; to which he replied, pointing to some evergreen trees, that their color was the same. A color-blind painter used green instead of vermilion in painting a red-checked face. Another painted a peagreen lion. A color-blind person has been known to put on together a red and a brown glove, thinking that they matched each other perfectly.
Mistakes such as have just been mentioned are perhaps of slight consequence. When, however, life or death depends upon the correct recognition of a color, as when red and green color-signals, flags, or lamps are used on railroads or at sea, then the existence of this not uncommon infirmity becomes a very serious matter. The object of Dr. Jeffries' book is to awaken a public sense of the importance of color-blindness as a disqualification in all posts of public and private service where individuals are called upon to recognize colored signals of any kind. He shows the dangers that may be occasioned by the existence of color-blindness in such persons. He also sets forth most minutely the methods by which color blindness can be unerringly detected and convincingly demonstrated, under all circumstances, whether the sufferer be conscious or not of his defect, willing or unwilling to let it be known. The book will therefore be invaluable as a complete repertory of information for all persons who, professionally or otherwise, are interested in the subject of color-blindness.
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