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Color-Blindness and the Railroads

People often assume that everyone else sees the world in the same way that they do, not just figuratively but also literally – the sky is blue, the setting sun is red, the bright yellow of a dandelion is clearly distinguishable from the other colors. Color perception adds nuance and variety to visual images. Yet many people live quite productively without a full range of color perception. They may not even know that others see differences where they do not. Color perception is not generally critical to human survival; it is not considered highly important and seldom limits any individual.

Blue-Yellow color blindness chart, from Tafeln zur Bestimmung der Blau-Gelbblind

However, if that individual is responsible for operating or interpreting color-coded traffic control signals, havoc can result. With the rise of the railroads in the 19th century came an increased number of accidents caused by the inability of some railroad personnel to appropriately recognize colors. This unacceptable situation stirred research into the causes of limited color recognition and practical diagnostic tests to screen out potential employees who exhibited sub-standard color perception.

The Rare Books collections of the Becker Medical Library contain several items concerning this interesting topic, including what may be the three earliest texts dedicated exclusively to the subject.

George Wilson's 'Researches on colour-blindness' reported his findings about the

The first seminal work is Researches on colour-blindness, with a supplement on the danger attending the present system of railway and marine coloured signals, by George Wilson, M.D. Published in Edinburgh in 1855, this book reveals that even medical people were still unaware of any anatomical reason for color perception. Wilson and his contemporaries acknowledged that incomplete color perception was far more common in men than in women, and often found within families. But they were unclear on the roles of “nature versus nurture.” Many of the individuals who exhibited color confusion in Wilson’s cited references and in his personal studies happened to be Quakers, so Wilson cautiously theorized that:

“the effect upon the great majority of Friends, of being surrounded from early infancy by neutral, subdued, or sombre tints, cannot be favourable to the development of an acute sense of colour… and the century and a half or two centuries which have elapsed since the forefathers of the present generation of Quakers adopted Quakerism, is sufficient to have permanently affected the Colour-Vision of not a few of their existing representatives.” (Wilson, p. ix).

Wilson’s inquiries into color perception were spurred by his personal observations that some students in his chemistry classes were apparently unable to recognize the visual changes caused by adding alkalis to other substances. Since these were bright and motivated students, Wilson concluded that some people genuinely could not distinguish the normal human range of the color spectrum. He extended the implications of this observation to other practical situations, and quickly grasped the potential for disaster with color-impaired railway signalmen.

To gather more facts and pursue his research, he asked the Royal Scottish Society of Arts to disseminate a request for unpublished case studies. Wilson was also permitted and funded by the Society to examine various local military, police, and student groups to enlarge his statistical evidence. Wilson determined that there were several prevalent types of color confusion and that 5 or 6% of the male population he studied were afflicted. (chart, Wilson, p. 72).

Green-Red color blindness chart, from Tafeln zur Bestimmung der Blau-Gelbblindhe

Wilson treated all of his subjects with respect and admired the adaptations they made to succeed among their more completely endowed peers. He was simply concerned with safety, concluding that “(t)he professions, for which colour-blindedness most seriously disqualifies, are those of the sailor and railway servant, who have daily to peril human life and property, on the indication which a coloured flag or a lamp seems to give.” (Wilson, p. 124). He was gratified that his research motivated the Great Northern Railway Company to require testing for its porters, but advocated that creating new standards of symbolism based on varying shape rather than color would be the best solution.

However, color signals remained the standard. Several decades after Wilson’s initial writings, there was continued urgency to understand the dangers of atypical color perception and its relation to railroad safety.

In 1877, Frithiof Holmgren published Om färgblindheten: i dess förhållande till jernvägstrafiken och sjöväsendet [Colorblindness and its relations to railroads and the marine] in Upsala, Sweden. The King of Sweden accepted Holmgren’ findings as an important safety advance, and promptly acted upon Holmgren’s recommendations. The book’s practical value was convincing and it was immediately translated into French, German and English. The Bernard Becker Medical Library is one of only a handful of libraries holding the original Swedish text.

The frontispiece of Jeffries' Color-blindness: its dangers and its detection fea

Benjamin Joy Jeffries in the United States was an admirer and personal friend of Holmgren, to whom he dedicated his book Color-blindness: its dangers and its detection, published in Boston in 1879. Jeffries was surprised to find that his was only the third monograph (after Wilson and Holmgren’s books) on the subject, although “the literature of normal and abnormal chromatic power is pretty extensive” (Jeffries, pp. viii-ix) as indicated in the numerous articles in many languages cited in his 17-page bibliography. Jeffries intended his book to reach a wide audience, from the curious general public to physicians and scientists, and of course railroad and marine authorities.

With the need to understand and diagnose color perception defects now apparent, the next step was refining a reliable testing method. In the late 1870’s, Jakob Stilling authored several works that were published in Cassel (currently spelled Kassel), Germany and are illustrated with plates of chromolithographs. Die Prüfung des Farbensinnes beim Eisenbahn- und Marinepersonal: The examination of the sense of colour of railway employés and pilots and Tafeln zur Bestimmung der Blau-Gelbblindheit offer early examples of the same system of alphanumeric symbols embedded in colored dots that are still widely used today.

In the light of modern medical knowledge, all of these books seem quaint. The inherited anatomical cause of most congenital color perception deficiency is now well understood, and the transportation industry regularly screens employees having pertinent responsibilities for color awareness. But these books offer fascinating historical documentation of why and how this pervasive and generally harmless human condition was finally recognized and explored. The individuals who are represented in the numerous case studies live again as they share their discovery that others apparently perceived something they simply could not comprehend, and their creativity is impressive as they reveal the varied adaptations they employed to compensate.



Frithiof Holmgren (1831-1897). Om färgblindheten: i dess förhållande till jernvägstrafiken och sjöväsendet. Upsala: Ed. Berlings boktryckeri, 1877.

Benjamin Joy Jeffries (1833-1915). Color-blindness: its dangers and its detection. Boston: Houghton, Osgood and Company, c1879.

Jakob Stilling, (1842-1915). Die Prüfung des Farbensinnes beim Eisenbahn- und Marinepersonal: The examination of the sense of colour of railway employés and pilots. Cassel: T. Fischer, 1877-79.

Jakob Stilling, (1842-1915). Tafeln zur Bestimmung der Blau-Gelbblindheit; diese Tafeln bilden die Ergänzung zu dem früher erschienenen Werk des Verfassers Die Prüfung des Farbensinnes etc. Cassel: T. Fischer, 1878.

George Wilson, (1818-1859). Researches on colour-blindness: with a supplement on the danger attending the present system of railway and marine coloured signals. Edinburgh: Sutherland & Know, 1855.


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