Dangers from color-blindness in railroad employés and pilots
Jeffries, B. Joy (Benjamin Joy), 1833-1915 | Royal College of Surgeons of England
V SS vssc- s * c cr V ^ jr. e z yi 's t &'Z &<7. r-p ^ L — ?S f 5 ^/cdtou/ Sftieef, S&cafcn, ^^faaa . , ^'.c^ftJ^f [From the Ninth Annual Report of the State Board of Health.] DANGERS FROM B. JOY JEFFRIES, A.M., M.D. (Harvard), Fellow Massachusetts Medical Society; Ophthalmic Surgeon Massachusetts Charitable Eye and Ear Infirmary, Carney Hospital, and New-England Hospital for Women and Children ; Member International Periodic Congress of Ophthalmology, American Ophthalmological Society, etc. BOSTON ; Eanto, 3bn:tJ, & &0., printers to tfje Cammonfocaltfj, 117 Franklin Street. 1878. DANGERS EROM COLOR-BLINDNESS, BY B. JOY JEFFRIES, M.D., OF BOSTON, OPHTHALMIC SURGEON, MASSACHUSETTS CHARITABLE EYE AND EAR INFIRMARY. 13 r ii l. ■ DANGERS ARISING FROM COLOR-BLINDNESS. It is quite commonly known, that there are certain people in the community who cannot distinguish ripe cherries or strawberries from leaves except by their form. It seems to be about equally well recognized, that this is only a sort of curiosity of no special importance to the community at large. When, however, it is remembered that the color-blind indi- vidual may be the engineer of a train running nearly a mile a minute to “ catch up time,” and that the passengers’ lives, not to speak of their property, are dependent upon his know- ing whether a switch is open or shut, or a draw up or down, by his instantaneously distinguishing between a red and a green light, then the community’s attention may possibly be aroused. Or, if another equally blind individual is pilot on a steamer, and cannot say whether the light directly ahead of the lives and property dependent upon his eyesight is red or green, and hence cannot know which way the sailing-vessel or steamer is moving in order to avoid collision, then the mere curiosity part of color-blindness sinks into insignificance in comparison with the danger arising from it. The community then awakens to a sense of the importance of asserting its rights. We may, however, suppose that the steamboat has several persons on the watch at the same time. This, however, would not prevent the helmsman of the heavily-loaded coast- er, perhaps the only man on deck, if he is color-blind, from mistaking the steamer-lights, confounding the green and red ; or he may miscalculate their distance, if he is partially color- blind. Such cases as these, which are sure to come into the courts on the question of damages, show us the dangers arising from this visual imperfection. The mortification, inconvenience, and loss of position or employment, from the lack of power to choose proper or appropriate colors in dress and costume, to distinguish and 3 4 STATE BOARD OF HEALTH. [Jan. match colored goods, to mix or use colored pigments, will not be here dwelt on. The dangers only to which the com- munity are subjected from color-blind railroad employes and pilots will be explained in this article, and how and why these should be avoided by the action of the community in protecting itself. For instance, an engineer has run on one road for some five or ten years without accident of impor- tance. The superintendent requires him to pass examina- tion by an expert, who finds he is markedly red-blind, and shows it most convincingly to the officials of the road. It becomes known ; and they then do not, of course, dare to keep him in his place. He is dismissed, to protect the com- munity from danger. Color-blindness is a partial or total inability to appreciate, as the normal eye does, one or more of the three so-called base colors. Scientists are at present pretty well agreed in regarding as the three base colors, red, green, and violet, or blue-violet. A large proportion of those who are color-blind are so in reference to red ; next come those who are green- blind ; and but rarely do we find persons violet-blind. Indi- viduals have been examined who were blind to two of the three base colors ; and there is record of totally color-blind persons, i. e., who had only an appreciation of light and shade. It must be distinctly remembered, that color-blind- ness does not necessitate any lack of power of sight as to form. On the contrary, the color-blind may possess extraor- dinary visual power, much above the normal eye as regards form, and may be able, for instance, to read letters much farther off than a person with a normal eye, not color-blind. It may here be observed also, that a person may be so blind as to form as not to be able to find his way about, or go alone, and yet have perception of colors and shades. To the color-blind all mixed tints, in the proportion which they contain his faulty color, will appear so much the darker. Where we see color, he simply sees the absence of it, if we may so say ; that is, an object of his faulty color appears to him as gray does to the normal eye. A red-blind person places a scarlet and a light gray together, as giving him the same impression. He will put on red pants or vest as readily as gray, or wear complacently a red and a green glove: When a red-blind person looks at the spectrum, or series of 1878.] DANGERS FROM COLOR-BLINDNESS. 5 colors from light passed through a prism, he will, towards the red end, fail to see any color where the normal eye con- tinues to see brilliant red; and the same will hold of the violet-blind, in reference to the other end of the spectrum, &c. This has an important bearing on the danger from color-blindness, as we shall hereafter see. A person who is red-blind cannot distinguish that color from green ; or, if blue- violet-blind, that color from yellow ; or, if green-blind, that color from its complementary one, red. Hence we have practically to deal with red-green blindness and blue-yellow blindness. These are, however, the very colors of necessity used on our railroads, sailing-vessels, and steamboats, as well as in many lighthouses. It is just one hundred years ago that cases of color-blind- ness were made public by Joseph Huddart. It was not till 1794 that the English chemist Dalton published an account of his own case, he being red-blind. Pierre Prevost of Geneva, in 1827, first called color-blindness Daltonism, and those so afflicted Daltonians. It is now, however, generally agreed to give up this use of so distinguished a man’s name ; and, as has been claimed, Daltonism should mean rather the doctrine of indivisible chemical atoms, and Daltonian a believer in such.1 In 1837 Professor A. Seebeck was the first to examine a number of color-blind, and classify their troubles. He also first showed that there were degrees of color-blindness, a very important practical point. Dr. George Wilson of Edinburgh, in 1855, in his book2 on color-blindness, says, “ My own special attention was directed to the subject from the blunders which I found my chemical pupils make in reference to the colors of compounds. After making every allowance for imperfect exposition on my part, and insufficient attention on the part of my students, and after also making a large deduction from inaccurate answers on the score of imperfect remembrance and inability to name colors, I still found, both in the laboratory and lecture-room, that many a pupil was puzzled to describe the changes which occur when an acid or an alkali acts upon a vegetable color- 1 I tise, therefore, the word “color-blind” throughout this article, instead of “Daltonism.” 2 I will not dwell on the literature of color-blindness, but refer to the list ol ■works at the end of Jhis paper, in the Alphabetical Bibliography. e STATE BOARD OF HEALTH. [Jan. ing matter, although to a normal eye these changes are of the most marked character ; and that in general I could count with little confidence upon accurate answers to questions regarding the colors of bodies.” Dr. Wilson found two color-blind among his class of students, and subsequently had opportunity of examining many others. I shall in this article often quote from Professor Wilson’s book, but will here give his closing sentences : “ The pro- fessions for which color-blindness 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 colored flag or lamp seems to give. Fortunately a ship is seldom under the guidance of a single person; and in her Majesty’s vessels the color-signal men are selected from a large number, and are ascertained to have a quick eye for color. In merchant-ships the choice must necessarily be made from a much smaller number; and the appalling yearly list of lost vessels which appears in our Wreck Returns awakens the suspicion that more than one of these fatal disasters may have resulted from the mistaken color of a lighthouse, beacon, or harbor-lamp, which on a strange coast, and with perhaps the accompaniments of a snow-storm or a thick fog, has been wrongly deciphered by a color-blind pilot. “ On railways the danger attending mistakes of signals is much greater than at sea ; especially in this country (Eng- land), where trains travel at a very high rate of speed, and succeed each other at very short intervals. The most marked peculiarities of the color-blind are shown in mistaking (1) bright red for green, (2) dark red for brown, (3) red for black, and (4) dark or light shades of all colors for each other. The caution signal green is thus liable to be mistaken for the danger signal red , and the latter (when it appears black) not to be seen at all. ... I am happy to say that the publication of my papers has induced the Great Northern Railway Company to require that in future all their porters shall be tested as to their freedom from color-blindness before they are admitted.” Dr. Wilson’s book and his efforts did not bear the fruit they deserved. No law has been passed by Parliament requiring 1878.] DANGERS FROM COLOR-BLINDNESS. 7 examination for color-blindness of all railroad employes in England, though warning has been also given there by Pro- fessor Tyndall, and across the Channel by Prevost, Noel, Favre, and Feris. In fact, twenty-two years after Wilson wrote and talked, a public journal, after speaking of the then recent accident at Arlesey, said, “ Hence, a systematic examination of the eyesight of those entering these services is impera- tively necessary ; and a definite report on the subject should be required of every examining surgeon. This would add but little to his labors, for the method of detection of the fault is sufficiently simple : the colored letters of Snellen’s test-types1 meet every need. If this is generally carried out, the public mind may rest contented ; for thus the congenital form of the color-blindness would be effectually recognized, and only those cases of loss of power of perception of color which come on gradually, and are symptomatic of disease of the optic nerve, or other parts of the nervous system, would remain undetected. These cases are relatively so few in number, and associated with so much general impairment of vision, that they need excite no alarm.” After the accident at Arlesey, a number of the English railroad surgeons reported that they had rarely found color- blindness amongst the employes. Now, this is readily ex- plainable when we come to inquire as to the methods of exam- ination for color-blindness in that country ; for we find they all depend upon the naming of colors by the examined. Till such methods as Wilson and Seebeck used, and which are now generally employed throughout Europe, are adopted and carried out by specialists or by surgeons particularly in- structed by specialists, color-blindness will not always be detected in railroad employes or sailors, and accidents from its existence will occur. An English journal well says, “ The testing itself is, however, or rather should be, a scien- tific affair. It cannot be hastily settled by showing a man a few pieces of paper, and asking him to name the colors.” Mr. Mason of Edinburgh would quiet public anxiety by say- ing in “ The London Times ” of Dec. 28, 1876, that “ care is taken to examine on most of the lines.” I would ask what tests are used, when any are used. 8 STATE BOARD OF HEALTH. [Jan. prove or disprove color-blindness by Snellen’s colored test- letters is simply ridiculous. It is, however, gravely recom- mended in what I have above quoted. I should state that I cannot here discuss this point at greater length, as I am of course to enter into no exposition or explanation of methods of examination for or detection of color-blindness. I have been, by experiment and observation, reluctantly convinced that it is impossible to substitute form instead of color for railway and marine signals ; and also am convinced that the best color for night is red , to mean danger, whilst black and white can be used during the day. When another color must be used, the best seems the complementary green by night. Black and white, or in other words form, can always be used by day. Now, this seems .to be what the rail- roads, especially of this country, are gradually coming to. Absolute safety, therefore, depends on the detection and refusal of all color-blind employes. The attention of railroad managers, and also that of the community at large, has been repeatedly called to the great danger likely to arise from color-blindness. I would, for in- stance, refer to Noel, in the “ Courier des Sciences.” And I would particularly call attention to the efforts of Dr. A. Favre of Lyons, France. I cannot do better than quote from the rSsumS of his memoirs. He says, “ I have proved by facts personally observed from 1855 to 1873-7, the neces- sity of testing for color-blindness all candidates for railroad service, and the exclusion of those who are red-blind ; also the necessity of specially examining employes who have beets injured about the head, those recovered from severe illness, smokers and drinkers. I call also for the periodic examina- tion of all in active railroad service. The majority of these precautions, adopted on the Lyons road since 1857, have been gradually enforced on other lines, and quite recently also on the Belgian roads.” “ Feb. 8, 1875, I called the attention of the ‘ Conseil de Santd des Armies ’ to the use of the colored signals employed in war, and the necessity of testing those giving or receiving orders by colored signals.” “In Feb- ruary, 1875, I called the attention of the Medical Society of Lyons to color-blindness caused by injuries.” “ On Nov. 4, 1875, 1 addressed the Medical Society of Marseilles in refer- ence to color-blindness in navigation. My conclusions were 1878.] DANGERS FROM COLOR-BLINDNESS. 9 adopted, and communicated to the marine authorities of the port, and the Minister of Marine. At ,the same time, the Academy of Sciences and Letters of Lyons voted to call to my publication the attention of the Ministers of Public Instruction, Public Works, War, and Marine.” Thus has not only the railway service been appealed to, to guard the community from danger, but the marine service also. Dr. Feris says, “ If color-blindness is considered a grave danger on railroads, how much more on the sea ! Colors are very important to the mariner : the flags, the side-lights, and even the lighthouses and buoys and beacons, present various colors. It is impossible for a helmsman or a signal- man to interpret or transmit signals if they have no appreci- ation of color. Errors with flag-signals are not so likely on board of vessels, as they are employed in daylight, and more often controlled by officers in charge. But the men at tele- graph stations are often alone, not under observation, and hence more likely to make mistakes. National flags may be mistaken, but more especially the white, red, and green Bengal lights used as night-signals.” “If good color-per- ception is necessary for a helmsman, how much more for the commander of a vessel I The increase of collisions at sea is an indisputable fact. How many remain unexplained, or referred to another cause, which are no doubt due to the color-blindness of a single man ! All vessels must now from sunset to sunrise carry a green light on the starboard and a red one on the port side. These show not only the posi- tion, but also the direction of movement, of the vessel.” “We can readily imagine cause for collision if the officers or watch of either of two vessels approaching are color- blind.” As the magnitude of the danger depends, of course, on the frequency of the defect, it becomes important to know in what proportion of the community it is likely to occur. Very variable statistics are given by different observers, de- pending largely upon the methods of testing for color-blind- ness ; the more thorough and scientific these latter are, the greater being the number of color-blind individuals found. Mistakes of excessive ratio reported are now better under- stood and avoided, since we know color-blindness runs in families, and is hereditary. An observer might thus find 10 14 10 STATE BOARD OF HEALTH. [Jan. out of 40 individuals examined, color-blind Let us glance at the statistics, such as they are, reportel by the earlier observers. Dalton found 8 to 12 per cent. Professor Pierre Prevost, 8 to 5^per cent. Professor Kelland of the Edin- burgh University found among 151 students 3 “ thorough Daltonians,” and several less well-marked cases. Wilson again found 2 among 20 students, one among 47 other students. On the Edinburgh police, five among 158. Dr. Rowe at the Morningside Asylum found 5 among 42 male attendants. These I quote from Wilson. Seebeck found 5 color-blind among 100 students. Professor Allen Thomson met with the same result as Dr. Wilson, as also D’Hombre- Firmas in France, and Professor Dove in Berlin. Dr. Wilson also examined a large number of soldiers, who together with those above spoken of as tested by him amount altogether to 1,154 persons. Amongst these all, 65 were color-blind, an average of 5.6 per cent, or one in 17.7. The red-blind were most numerous throughout all these. This proportion has been now admitted by Professor Helmholz. Wilson said in 1854, “The statistics of color-blindness are as yet very im- perfect, and do not include females ; but there is ever3r rea- son to believe that the number of males in this country (England) who are subject in some degree to this affection is not less than 1 in 20, and that the number markedly color-blind, i.e., given to mistake red for brown, brown for green, purple for blue, and occasionally red for black, is not less than 1 in 50. We may thus, according to our present knowledge, regard two in every hundred of the community as seriously defective in their perception of color.5' Dr. Goubert estimates 1 in 25 color-blind. Dove in his memoir of 1872 gives the following figures : Among 860 men, there were 40 color-blind, 4.65 per cent, or 1 in 21.5 ; among 611 women, 5 color-blind, or 0.82 per cent, or 1 to 122. Among 1,016 scholars at the Lyons Lyceum he found 16 color-blind for red and green, on a visit made in April, 1877. The last report of Dr. Favre, of the Lyons Mediterranean Railroad, gives the results of examinations of railroad em- ployes since 1855 ; it shows also how more careful tests dis- cover a greater proportion of color-blind persons. Dr. Favre up to 1855 had examined about 5,000 candidates for railroad work, and rejected more than 50 for being red-blind. He had 1878.] DANGERS FROM COLOR-BLINDNESS. 11 not, unfortunately, kept accurate records. From 1 855 to 1 804 he noted 8 color-blind only, which number does not corre- spond with the number of men examined. From 1862 to 1872, among 1,196 persons, he refused 14 color-blind who could not tell red. From May, 1873, to July, 1875, his exam- inations were more particular and exact ; and he found among 1,050- persons seeking railroad employment, 98 who made decided blunders or hesitated ; 10 were refused for being red- blind. His new series since 1875 comprises 600 examina- tions : the results of these he has not yet sent me (January, 1878). 728 men already in employment were examined in 1872—73. More than one-third of these had been previously tested for color, and the red-blind eliminated. Of these 728, 42 either made mistakes or repeated hesitations. Among 224 conductors examined by Dr. Favre and M. Git, 14 were found decidedly color-blind. In 1874 he found 4 color-blind among 75 office-clerks ; the same year, 24 among 65 firemen at the Perrache gas-works. At the Ouillins works, among 148 workmen, whom he examined in August, 1877, 82 told the five elementary colors without error or hesitation : 56 either hesitated or made mistakes. May 7, 1877, among 155 students at the veterinary school at Lyons, Dr. Favre found 19 hesitate or make mistakes. Examining with Capt. Belle- cour 268 sub-officers and men of the 16th line, he found 105 color-blind or color-deficient. Among 138 men of the 22d, 23d, and 99th line, M. Paul Guillot found 37 color-blind. Lt. Gallet of the 26th Artillery, in garrison at Mans, exam- ined 116 young soldiers, and found 32 who hesitated or made mistakes on a color-scale of 15 shades. Lt. Lautheaume found 40 color-blind among 132 men of the train of the 26th artillery. The average among this series of 654 young sol- diers was 32.72 per cent. Dr. Mourand, among 200 men of the Lyons station, found 7 color-blind. Dr. Favre says his colleague must have noted only the most marked cases. Dr. Feris, in his pamphlet and more recently in a commu- nication to Dr. Favre, reports having examined 775 officers and sailors, amongst whom he found 75 color-blind; 19 wholly confounded red and green. The average of this series is 10 in 100. Of all the adults Dr. Favre examined, the average was 16.84 to 100. He says, “ The results will vary greatly, being dependent on many circumstances and pecu- 12 STATE BOARD OF HEALTH. [Jan. liarities I shall hereafter notice ; but we may be assured, that in France the color-blind amount to 10 in 100 of the adult males.” I must for brevity omit Dr. Favre’s similar reports as to children and the aged, as well as the interesting results he obtained from observers in the French domain of North- ern Africa. Dr. Favre says, “ The study of color-blindness interests at least a tenth of our population (France). This very large proportion gives us the measure of the chances of error the color-blind run in the various industries where good color- perception is necessary or useful. It does not, of course, give us an exact idea of the chances of accident at sea and on railroads, on account of the accessory circumstances which aid the color-blind in his embarrassment; but it shows us plainly how numerous the chances are.” My friend Dr. Edmund Hansen, a distinguished ophthalmic surgeon of Copenhagen, Denmark, writes me June 24, 1877 : “ The railways of Denmark are in the possession of two parties : one is a private company which owns the railways of the larger island called Sealand, and of the adjacent smaller islands Lolland and Falster; whereas the railways on the island Tyen and on the peninsula Jutland belong to the government. The investigation for color-blindness has just been completed by the private companies ; on the government railways it will be done in the course of the summer. (I will give you the results of the private company, and shall send you the other when the results have been made known.) The examination on the Sealand, Lolland, and Falster roads has been made according to the method of Professor Holmgren of Upsala, Sweden. 1,084 persons were examined, of whom 50 were women. Of this number, 81 men, or 2.87 per cent, were color-blind, all congenital cases ; none of the women were color-blind. Of the 31, 10 were perfectly color-blind, 21 imperfectly. Of the perfectly color-blind, 6 had red-blind- ness, 4 green-blindness. Their occupations were, 2 station- masters perfectly green-blind ; 1 engineer perfectly red-blind ; 1 train-conductor, 1 fireman, perfectly green-blind ; 4 porters, 3 blacksmiths, 7 railway guards, of whom 2 were perfectly red-blind ; 2 assistants, 1 pupil, perfectly red-blind ; 1 con - cierge, 2 foremen, of whom 1 was perfectly green-blind ; 4 workmen on station, 1 perfectly red-blind ; 2 extra conductors, 1878.] DANGERS FROM COLOR-BLINDNESS. 13 1 perfectly red-blind. Dr. J. Stilling of Cassel, also, writes me, Dec. 6, 1877 : “ I have but once had opportunity of examining railroad em- ployds, about 400 in number ; of these 6 per cent were color- blind.” He has invented and published some new tests for the imperfection, and says : “ A number of the railroad cor- porations are turning their attention to color-blindness, and the time is not far distant when we shall have official and complete examinations of all employds.” The Bavarian government railroads have ordered a similar examination for of all their employds. Unfortunately their printed instructions were not drawn up by a specialist, one familiar with Professor Holmgren’s method, and are hence severely and very properly criticised by Professor J. Michel 14 STATE BOARD OF HEALTH. [Jan of Erlangen. He says he has employed Professor Holmgren’s method, and can wholly recommend it. , It is stated that “ an optical examination has been ordered by the Minister of Ways and Communication, at St. Peters- burgh, of all persons connected with Russian railways, in order that their power of distinguishing colors may be tested. It appears that the order has been issued in conse- quence of the startling results lately obtained from a similar examination of railway employes in Finland.” Dr. A. Lederer has lately found 63 color-blind persons amongst 1,312 men of the Austrian navy, or 4.8 per cent. In the statistical memoirs of the United States Sanitary Commission published in 1869, the compiler, Dr. B. A. Gould, says, “ Few observant persons, in our own community at least, can have failed to be frequently impressed by the comparatively large number of persons who are more or less unable to distinguish between colors the most strikingly con- trasted. The ordinary intercourse of daily life does not usually attract attention to this peculiarity ; but, when any accident has brought it to our notice, we are surprised at dis- covering its existence in some familiar acquaintance in whom it had never occurred to us to suspect it. Persons who can- not distinguish ripe cherries upon the tree, or strawberries on the vine, by their color, are far more numerous than would be suspected by those who have given no attention to the subject ; and unless some grotesque incongruity in costume, or some remarkably inaccurate description of the color of a well-known object, compels our notice, we remain unaware of the imperfection. Serious misunderstandings or calamities have been reported in the army, resulting from mistakes in the color of green and red lights by officers of the signal corps, themselves not fully aware of their failing in this respect ; and cases have occurred when ludicrous and even disastrous results have followed the use of a badge of pre- cisely the wrong color.” Instructions were issued to test for color-blindness ; and in the reports received, “ the descrip- tions of the irregularities manifested in distinguishing colors are in general neither complete nor adequate, owing probably to insufficiency of the instructions given.” Among 8,831 white men, 161 were found color-blind, equal to 0.02. This small ratio is of course due to the crude method of examin- 1878.] DANGERS FROM COLOR-BLINDNESS. 15 ing, which would only detect the most marked cases of color- blindness. Dr. Gould says, “ Notwithstanding the incom- pleteness of the descriptions returned, and the consequent inadequacy of the classification, the well-known fact is dis- tinctly manifest, that the most usual form of color-blindness is that which fails to distinguish between the green and red, and that the confusion of colors sometimes embraces the other half of the spectrum, and sometimes its entire range.” The great variation in the ratio of color-blind persons, reported by different observers, is readily explained by differ- ences in the accuracy of the method of testing. In testing color-perception by the sun’s spectrum thrown on a white surface, the color-blind observer will see the color he is deficient in over a smaller surface. Dr. Ed. Rgehlmann, in Ilalle, reports the test of 70 people with the sun’s spec- trum. He found only 80 of them saw the red normally : the others varied in their red perceptive power. He tested only 20 as to the violet end of the spectrum, and found remarka- ble shortening of the visible portion for this end also. He noticed also that when the red end of the spectrum was shortened, the violet was also reduced, limiting the spectral row of colors on both ends. I have recently employed Professor Holmgren’s method in testing 611 instructors and students of the medical depart- ment of Harvard University and the Institute of Technology. Amongst them I detected 30 color-blind, being very nearly one in twenty, — not a large ratio for the whole community. In a society of some sixty or seventy gentlemen, after I had spoken on this subject, three persons, besides one other whom I knew was color-blind, reported to me that they suf- fered from this visual imperfection. Still another told me his child was color-blind, as had been his wife. I have perhaps quoted enough to show by statistics, and by the precautions railroad corporations in Europe are tak- ing, the extent to which color-blindness prevails. But I should quite fail in giving the subject due prominence as to the prevalence of color-blindness, the value of scientific investigation in detecting it, its danger for the community, and the success of true methods of testing in convincing railroad people of all this, &c., were I not to quote from 16 STATE BOARD OF HEALTH. [Jan. Professor Holmgren’s work. His method of examination has been generally adopted wherever railroad surgeons are testing the employes, and consists in the use of worsteds of various colors, whereby the person examined does not name the colors at all, but simply selects them by comparison with the test. By it, a number of eyes can be tested for color-blind- ness in a relatively short time, whilst it does not call for any special intelligence on the part of the person examined. Its operation, moreover, requires but little necessary prepara- tion or apparatus. It is on the principle of one used more than twenty-two years ago by Dr. Wilson, but since neglected. I take the liberty of reproducing from Professor Holmgren’s book (translated) as follows : — “In a case called the Lagerlunda, arising from a railroad acci- dent at Lagerlunda, in Ostrogothie, Nov. 15, 1875, and which ex- cited great public attention, there was evidence leading me to suppose that color-blindness was one of the principal causes of the disaster. This led me to think that control should be exer- cised among railroad employes as to color-perception. “ In June, 1876, I had an opportunity for testing this matter. By the courtesy of Major-Gen. von Knorring and Major Rudbeck, I was permitted to examine 2,200 men of the infantry and dra- goons of the guard in camp in Upland. The extreme simplicity of the method was shown, and its ready adaptation both as respect rapidity and certainty. The examination averaged one minute to a man, often less ; and, by the improved method adopted, we de- tected also with certainty all those partially color-blind. From this examination we learned, in reference to the existence of color- blindness among the population of the province, that out of the 2,200 men, 11 were red-blind, 17 could not perceive green, and 1 violet (?) ; 31 besides were incompletely color-blind in accordance with my classification. There were, then, 60 defective, or 2.7 per cent. The cases of ‘ feeble sensation of colors ’ are not here in- cluded. “ July 14 of the same year, I had opportunity at the Scandina- vian Medical Congress assembled at Gotkembourg, to describe my method, report the results of its employment, and also to express my views as to the necessity of taking measures on a large scale in reference to the detection of color-blindness, especially among railroad employes. In consequence, the Congress voted unani- mously on the necessity of instituting examinations to detect color-blindness first among railroad employes, second among 1878.] DANGERS FROM COLOR-BLINDNESS. 17 pilots, lighthouse-keepers, and sailors in general, and third in the schools. During the Congress I had time to show the phj'sicians the practical application of the method, by examining in their presence, by permission of Col. Carlsohn, 100 men of the artillery- regiment in Gotha, amongst whom we found 4 color-defective, 1 for red, 1 for green, and 2 incompletely blind to color. At the same time I found one green-blind among the physicians, members of the Congress, and one red-blind among the assistants. “ I was then prepared to apply directly to the railroad adminis- tration. Thanks to the press, which followed attentively the dis- cussions in the Congress of Gothembourg, the question came to the knowledge of the public. It naturally attracted the attention of the railroad employes, who for the most part looked upon it with a certain distrust, as rather the result of learned imagination or over-solicitude, than as a practical matter for the railroad ser- vice. We have heard a railroad emploj’e use almost literally these words : ‘ If color-blindness really exists, it cannot be amongst the employes, or it would have been noticed. This must at least be the case with the engineers and conductors, all of whom obtain their places after passing through inferior grades, and con- sequently after having sufficiently proved their faculty of distin- guishing colors.’ It was therefore very important to obtain some certain data on this point. This soon arose. Mr. Jacob- sson, chef Sexploitation of the Upsala-Gefle line, asked me to accompany him on a tour of inspection, and examine all the emploj'es under his orders. The tour was undertaken in the fall ; we left Upsala Sept. 7, and to carry out our examinations halted at all the stations, at all the guard-houses, and at every gate ; in short, we stopped at every point where an employe was to be found. The examination was finished at Geflc, Sept. 8. All the force, 266 men and women, were tested. Amongst them we found 13 defective; viz., 4.8 per cent. Six were completely green-blind , and 7 incompletely color-blind. Their positions were, 1 chief of station, 1 engineer, 2 conductors, 1 chief of equipments, 2 men of the equipment department (one a supernumerary), 2 overseers, 2 road-guards, 1 clerk, and 1 stoker. Immediately after the examination the chef d’ exploitation dismissed all those wrho were blind for green. “This first expedition was interesting in many respects. It showed that the method of examination was adapted to and could be used on the failroads. It showed moreover, that there were really color-blind, in nearly every degree, employed on the Swed- ish roads, of which no one had had the slightest suspicion. “ In Finland Dr. L. Krohn, who was by correspondence instruct- 15 18 STATE BOARD OF HEALTH. [Jan. ed in the method and principles applied in Sweden, has already examined the personnel attached to the railroads of his county. A locomotive and car were placed at his disposition to enable him to test the employes on the whole length of the line. It was completed in twelve days. He found, among 1,200 persons tested, 60 color-blind, namely, 5 per cent. They were as follows : 4 red-blind, 25 green-blind, and 31 incompletely blind.” Professor Holmgren brought this matter before the various railroad directions in Sweden. Moreover, experiments were made in the Physiological Institute at Upsala, so that by Nov. 9, 1876, throughout Sweden, it was ordered that all the railroad employes should be tested for color-blindness by the methods there used. What Professor Holmgren has accom- plished leaves no excuse for our American railroads in hesi- tating or refusing to thoroughly and properly test all their employes for defects of color-perception, and dismissing those who are color-blind, and providing also for the future by test- ing all applicants for employment. If long before this my readers have been astonished at the facts here collected, they no doubt have also been equally disposed to question them, or at least their practical bearing. They will naturally say, “We do not hear of railroad acci- dents from color-blindness, and rarely of marine collisions attributable to this cause.” Of this I shall again speak, but I must first here explain how it is that the color-blind get on so well, conceal their defect, and perhaps avoid accident. I shall confine my remarks to the railroad personnel and mariners. Professor Holmgren explains this so readily from his experience, that I do best to first quote from him. He says : — “We should imagine a color-blind railroad employe would be immediately detected, or would have at least discovered his own defect. This very natural idea has greatly tended to retard the reform we have called for. It is, however, incorrect, and docs not stand the test. On the contrary, examinations showed that a large number of color-blind were employed in nearly all the positions on a railroad, without they or others being aware of their faulty color-perception. And further, a number of these, far from being convinced of their defect, even after the examin- ation, insisted on repeating the test (even six or seven times), giving all sorts of excuses in explanation of their constant 1878.] DANGERS FROM COLOR-BLINDNESS. 19 mistakes. They all agreed in saying that they had excellent sight, never had experienced the slightest difficulty in distin- guishing the signals, and though a long time in service, and in most important posts, as locomotive-engineers for instance, never had made the slightest mistake. “ Certainly we may well be astonished at this condition of things, and very naturally ask how it is possible for an}' one to perform the duty of engine-driver, for instance, any length of time without exposing a deficiency of vision so important for the performance of this duty. There are, so far as we know, only two explana- tions : one is in the peculiar visual sense of the color-blind, and the exercise of this sense in distinguishing the signals ; while the other depends on the conditions under which an engine-driver ordinarily does duty. “ As to the first explanation, we must remember that every color coming from an illuminated colored surface may be more or less bright or dark, and every lantern-light, even colored, may be stronger or weaker. Hence, in a colored object or colored light, the e}'e does not alone take note of the color or quality of the light, but also of its quantity or intensity. When two objects or two lights appear of the same color to the eyes of a color-blind person, they may differ as respects intensity. This being the sole difference between these lights, it is particularly noted ; and thus, often as a result of special exercise, such color-blind person may strengthen his perception so as to in a certain degree make up for his color-deficiency. He resembles somewhat the persons who, deprived of one sense, replace it to a degree, by the greater exercise of one or more of their other senses. We have already noticed this point, so very important in practice, but could not refrain from again reverting to it here. Any one who has expe- rience from conversation with intelligent color-blind, or experi- menting with Maxwell’s rotating disk, will have noticed their peculiar sensitiveness to varying intensity of light, whilst compar- ing two colors, and hence can have no doubt as to how a color-blind person can so often distinguish between railroad signals, and give the colors their true names. “ Did we not know this, we should be greatly astonished to find with what facility a color-blind railroad employe can distinguish between the red and green flag, and generally call the red, green, and yellow lanterns b}r their right color ; but it is the intensity of the light, and not the color, which governs his decision, and this is the whole secret. The flags and lanterns have, in fact, usually a constant difference as to intensity. The green flag is to the color- blind, as also to the normal eye, undoubtedly of the deepest or 20 STATE BOARD OF HEALTH. [Jan. darkest color, and tlie red the most brilliant. As to the lanterns, the red-blind always recognize the red light by its being darker than the green, and the yellow by its being clearer or more bril- liant than the other two. The green-blind finds also, in his turn, the red more brilliant than the green, and distinguishes it by this. “The other explanation lies in the conditions under which an engineer has to observe the signals. First of all, we must remem- ber the great regularity with which all the details of railroad service take place. An engineer starting from a station at one end of the line knows very well in advance what stations to stop at, and which to pass. Under ordinary circumstances, he knows which light ought to be exhibited on the signal-posts above the several stations. The hand-lanterns are not as important, since their color is not so essential, being supplemented by movements. Hence it is only under exceptional conditions that accidents can happen at stations, from mistakes as to the color of fixed lights. There may, of course, be a number of other cases exceptional to the ordinary regularity ; but we must here notice one circumstance which probably has been and still is of very great importance ; namely, that the engineer is not the only one who has to watch for the signals. There is always with him the stoker, and near him a conductor, an oiler, &c., to aid him at critical moments. It must be extremely rare that all the personnel of a train are affected with color-blindness. “ Considering only practical^ the fact mentioned, and the expla- nation we have given, one might perhaps imagine that color-blind- ness had some scientific, but hardly any practical interest, and hence that all the talk that has been made about it in railroad em- ployes in our country was unnecessary, because, as may be said, the color-blind have often been employed a long time in railroad service without its being noticed, and without accident or the slight- est inconvenience arising ; and finally, that, since the}7 can really distinguish the signals (although this is otherwise than by color) , their kind of blindness need not call for any preventive measures. It is thus that a great many persons still reason. “We do not stop here to give the testimony of experience on this point in our country. One fact is certain ; namely, that color- blindness in other countries has caused numerous and very fatal accidents. Even if this had not been definitely proved, it is none the less evident that we have no right to await another such experience before passing to words and acts, and in every way showing, that, notwithstanding the numerous circumstances which assist the color-blind in responding to the signals, danger is not 1878.] DANGERS FROM COLOR-BLINDNESS. 21 wholly avoided, and the uncertainty remains. This is readily shown. Neither the fact that the color-blind have been employed many j-ears on the railroads without causing accident, or even without their defect being discovered, nor the circumstances we have cited in explanation of this fact, furnishes the least assurance of security. “A typical color-blind person cannot distinguish between red and green. This is an incontestable fact, readily explained by theory, and sufficiently proved by experience. All his judgment as to the difference of colors rests, in consequence, on conjecture. If perhaps, exercise enables him, up to a certain point, to distinguish between the red and green railroad lights, this is dependent on the intensity of the light telling him the color. But there is, of course, great uncertainty in this means of reading the signals ; and the man who may be right in a certain number of special cases will surely go wrong in some other. It is a principle not dependent on theory, but confirmed by our experience in exam- ining more than two hundred color-blind ; and we may extend it beyond the limits we have here kept, in other words, to the ma- jority of cases also of incomplete or partial color-blindness. 