A NEW WOOL-TEST FOR THE DETECTION OF 
COLOR-BLINDNESS- 
BY . 
WILLIAM THOMSON, M.D., 
PROFESSOR OF OPHTHALMOLOGY IN THE JEFFERSON MEDICAL COLLEGE ; SURGICAL 
EXPERT TO THE PENNSYLVANIA RAILROAD COMPANY, ETC. 
OF PHILADELPHIA; 
FROM 
THE MEDICAL NEWS, 
August 18, 1894. Reprinted from The Medical News, August 18, 1894. 
A NEW WOOL-TEST FOR THE DETECTION OF 
COLOR-BLINDNESS. 
By WILLIAM THOMSON, M.D., 
OP PHILADELPHIA ; 
PROFESSOR OF OPHTHALMOLOGY IN JEFFERSON MEDICAL COLLEGE ; 
SURGICAL EXPERT TO THE PENNSYLVANIA RAILROAD COMPANY, ETC. 
The new test herewith presented is based upon 
and is a simplification of and improvement on the 
“ color-stick,” an arrangement of wools adopted by 
the Pennsylvania Railroad Company in 1880, and 
described in their instructions for the examination 
of their employes, and further in The Medical 
News of January 14, 1882; in the Diseases of the 
Eye, by Nettleship; and in the Popular Science 
Monthly for February, 1885, under the title of 
“A Practical Examination of Railway Employes as 
to Color-blindness, Acuteness of Vision, and Hear- 
ing.” 
The entire system has been continued on the 
Pennsylvania Railroad unchanged, giving full satis- 
faction, and is used as a barrier before every new 
employe to protect the road from the admission of 
dangerous men. It has been adopted by the Phila- 
delphia and Reading Railroad Company and by 
others, as is shown by the replies received in re- 
sponse to a circular recently sent to a hundred of 
the most important railroad corporations of this 
country, controlling 129,970 miles, asking if exami- nations were made as to color-blindness. Thus, it 
was found that 
Those using Dr. Thomson’s test controlled 38,786 miles. 
Those using other methods controlled 15,679 “ 
Those making no test controlled 29,428 “ 
Those making no reply controlled 46,077 “ 
Sixteen other roads having control of 12,947 
miles have also adopted my color-stick, thus making 
a grand total of 51,733 miles protected by this 
test out of 142,917 covered by the investigation. 
The total number of roads included is 116 ; of these 
40 use my color-stick; 11 use other color-tests, 
mainly Holmgren’s; 31 use none; 34 have made 
no response. The entire system has also been in 
use on the Midland and on the London and South- 
western in England. 
The Pennsylvania Railroad system has accom- 
plished much good, but there is yet much to be 
done to bring all the roads in the country under 
the protection of some efficient method of testing, 
to secure both the roads and the public against loss 
of life and property from these well-known defects 
of their employes. The total mileage of the coun- 
try is 175,233 and there are 1,000,000 employes. 
The protection of over 50,000 miles of track by 
one system is an efficient answer to the charge from 
England, where the total trackage is but 19,288 miles, 
that nothing had been done in the United States 
beyond the passing of a law in the State of Alabama 
on this subject. 
As the result of much experience, and after a 
recent study of the entire subject, I would suggest 
some improvements that will enable a new test to be used in connection with the color-stick or as a substi- 
tute for it. The color-skeins of this new arrangement 
have been most carefully selected, and a standard 
set will be kept, so that renewals may be made of the 
entire set or of those skeins that may become faded, 
soiled, or lost. The new set consists of a large 
green and a large rose test-skein, and forty small 
skeins, each marked with a bangle having a con- 
cealed number, extending from i to 40, placed in a 
double box, so arranged as to keep the two series 
apart and to permit each to be exposed upon a 
table in a confused mass. The stick is dispensed 
with, as giving too fixed an arrangement to the 
skeins and not enough confusion, although the 
skeins could be readily removed from their hooks 
and changed in position for this purpose. 
The large green skein being placed near by, the 
small skeins from one to twenty are exposed in good 
daylight, and the employe under examination is 
directed to select ten shades of the same color of 
the test-skein. One with normal vision will choose 
promptly and with ease the ten greens with odd 
numbers on the bangles. A color-blind person will 
hesitate, and his selections will contain some even 
numbers, and the confusion-colors will be shades of 
brown, etc., containing some red, or shades of gray, 
and will indicate the color-defect. These figures are 
to be recorded on a blank, and the t wenty skeins are 
to be removed. The large rose skein is then used and 
the examination repeated in like manner with skeins 
numbered from 21 to 40, and the result recorded. 
The confusion-skeins, which have even numbers, 
are blue, green, and gray. From the selections 4 
made by the man found color-defective by the green- 
test, we are able to decide the character of his color- 
blindness. Those selecting blues are red-blind; 
those taking greens and grays are green-blind, ac- 
cording to the nomenclature of Holmgren. There 
are ten roses and ten confusion-colors in the second 
series. 
The red test-skein of the stick, with its confusion- 
colors, is omitted entirely, and the test is made to 
conform more strictly with Holmgren’s method, 
while the examiner is also provided with forty 
questions of decisive clearness. Greater scientific 
accuracy is obtained by this method, and with the 
careful selection of these confusion-colors I now re- 
gard this system as an improvement upon the 
stick, and as a safer and more simple method to be 
used by a non-professional examiner. The blank 
will also give to the division superintendent or to 
any supervising surgical expert a more simple report 
of the examination. The yarns are to be kept from 
the light in the double box, one side of which is 
colored green and the other rose, to aid the ex- 
aminer in keeping the series separate and to save 
time. The test will be a valuable addition to those 
to be used by surgical experts. 
In order to show how the Pennsylvania Railroad 
Company keeps its records of these examinations we 
submit the following fac-simile of an actual blank: 
WEST JERSEY RAILROAD COMPANY. 
Examination of sight and hearing of James A. Morris, aged 
twenty-two, employed as locomotive fireman, applicant for 
Camden, January 19, 1883, ACUTENESS OF VISION. 
The number of the 
series seen at twenty 
feet distant. 
RANGE OF VISION. 
Least number of 
inches at which type 
D—0.5 in test-type 
pamphlet can be read. 
Right eye, 
inches 
Left eye, 
4% inches 
Right eye 
Left eye 
20-30 
20-20 
FIELD OF VISION. 
Good or defective ... Good. 
Color-sense. 
Test-skein 
submitted. 
Name 
given. 
Numbers selected to match. 
A—Green 
B—Rose 
C—Red 
Green 
Red 
Red 
3,26,24,7,11,22 IS,S,I, 17.28,9,19.30. 13 
37. 33. 29, 12, 39, 31, 21, 35, 25, 27, 23 
37. 33, 31. 35, 23 
Second Color-test. 
Third Color-test. 
Number Name 
Numbers 
Flag 
Name and Numbers 
shown. given. 
selected. 
shown. 
use given. selected. 
Soiled 
Safety, 
24 Green. 
26, 22. 
White. 
White. | 2, 4, 6. 
39 1 Yellow 
Could find 
Soiled 
Caution, 
red. 
no match. 
Green. 
Green. 36, 38. 
Soiled 
Danger, 
30 Blue. 
26. 
Red. 
Red. 37, 33, 31 
Selection prompt or hesitating: 
Prompt. 6 
Hearing. 
Right Ear. 
Left Ear. 
Watch. 
Conversation. 
Watch. 
Conversation. 
8 feet. 
20 feet. 
8 feet. 
20 feet. 
Remarks: 
Escaping steam prevented watch-test. 
J. J. Burleigh, Examiner. 
Acuteness, right eye defective. Range, good. Field, good. 
Color-sense, defective. Hearing, see Remarks. 
JOS. Crawford, Superintendent. 
Note.—Those approved, marked “ Appd.” 
Those not approved, marked “ Not Appd.’ 
It may be of service to present to the surgical ex- 
perts in charge of the examinations of the various 
railroads the means that I have adopted for my own 
guidance in giving my final decisions. From the 
numerous methods described by scientific authorities 
I have selected ten that are practical, simple, and 
especially fitted for the detection of color-defects in 
employes of railroads. A book of record should be 
kept in which each case, with the results of the test- 
ing, should be entered. The Pennsylvania Railroad 
system provides that the preliminary examination 
should be made under the direction of the division- 
superintendent by non-professional examiners, but 
it is to be under the supervision of one professional 
competent surgeon, who is known as the surgical 
expert, who becomes responsible for the qualities of 
the tests, and who gives the final decision in all cases referred to him. Thus the men are protected 
from the errors of lay-examiners, and do not lose 
their places until pronounced defective by profes- 
sional authority. With ordinary care no color- 
blind man should escape detection by the lay-ex- 
aminer, but men really fit for the service might be 
unfairly treated. 
When referred to the expert the man found color- 
blind will present himself with the blank of his 
examination, and the surgical expert will then cor- 
roborate this by the following means: 
1. The stick or the new test-skeins; or both. 
2. Holmgren’s set of one hundred of fifty various- 
colored skeins will be used and the proportion of 
mistakes recorded. 
3. Browning’s pocket spectroscope will then be 
used, and the man be directed to describe the colors 
he sees when looking through the instrument. If 
color-blind he will say that he sees but two colors, 
yellow and blue, with a gray or a neutral band be- 
tween then. 
4. The color-tables of Stilling will then be used; 
these are so arranged that on a colored background 
letters and figures are printed in the confusion-colors 
of this background so as to be indistinguishable by 
the color-blind. 
It now becomes requisite to test the central vision, 
and to determine the power to perceive the signal- 
colors that are used by night. 
5. A piece of dark cobalt-blue glass should be 
used in the trial-frame over each eye separately, and 
the man be directed to look at the flame of a can- 
dle or other small light, from a distance of twenty 8 
feet. An eye normal in refraction and color-sense 
sees the light, colored rose or pink, surrounded by 
a blue halo. To a hypermetrope there may be a 
blue light, with a ruby-colored ring or halo; but 
two colors will always be seen, whilst the color-blind 
man sees but one color, blue, or a light spot with a 
blue halo. 
6. Donders’ instrument has a standard candle in 
a dark cylinder, with a wooden disc, and pieces of 
red, green, blue, and white glass so arranged as to 
be rotated in turn in front of the flame. Here also 
there is a metallic slide, with perforations ranging 
from one to twenty millimeters in diameter. The 
man is placed five meters away, and while the 
colors of the light are changed by rotating the disc 
he is challenged to designate the colors of the 
transmitted light. The normal eye recognizes them 
through the i mm. opening at 5 m.; or, better still, 
the candle is so placed that the examiner with normal 
color-sense just perceives the color through the 1 mm. 
opening at 5 m. The color-blind individual may 
fail through a series of openings until the 20 mm. 
one is presented. He may still call white green, 
and red green. If so, he is asked the significance 
of the green, and answers “ caution.” He is then 
requested to approach the light slowly, and as he 
does this he may perhaps at one meter or one-third 
of a meter, by its intensity or size, recognize and 
call it red. Using the same ratio for his color- 
blindness as we employ for his acuteness of vision, 
we can reason thus: Full color-sense enables one to 
see the lights promptly at 5 meters through the 1 
mm. opening; if the man sees them only after the 9 
apertures have been increased, his color-sense must 
be defective. Thus, if an opening of 20 mm. is 
needed, the color sense = -£$; should the man fail 
with the 20 mm. opening at 5 m. he is told to 
approach it, and if he sees it at 1 m. he has 
of color-sense, and if at of m., or 1 foot, he has 
only of the normal power. The mere diminu- 
tion of white light, by interposing pieces of London 
smoke, may induce the color-blind to pronounce it 
in turn white, green, and finally red. 
7. A tin lantern, with a switchlight condenser 
having a four-inch opening arranged so as to admit 
of placing pieces of white (ground), green, red, 
blue, and London-smoke glass before it, is now 
employed. This could also be made to take the 
place of Donders’ instrument, if covered with a 
front, and with a sliding-piece with small perfora- 
tions. A man failing to recognize the light from a 
four-inch aperture leaves no possible room for 
doubt, and this fixture is useful in convincing the 
friends of the man, and any railroad officers who 
may desire a rude test. The light is in diameter 
100 mm., and should be seen at 500 meters. 
8. The instrument of Mr. Carter, of London, 
is then made use of. This is to guard the surgical 
expert against a hasty opinion, and is to act as a 
check upon all wool-tests. It is based upon the 
sensibility of the retina and its power to recognize 
form and color in various intensities of light. The 
surgeon and the man examined regard the tests 
simultaneously while the quantity of light is varied ; 
thus, possible errors with other tests, especially 
Holmgren’s, can be avoided. 10 
9- In Dr. Chibret’s instrument, by means of 
polarized light various colors may be produced at 
will. The color-blind betray themselves by placing 
the instrument so that two dissimilar discs of light 
appear to them alike. 
io. Finally, an assortment of flags that have been 
in actual use, ten of each color, white, green, 
blue, and red are used as a test. These are thrown 
down in a confused mass on the floor, and the man 
is directed to properly assort them. Astounding 
mistakes are often made; as, for example, when a 
man is directed to take a red flag and use it to 
protect the rear of a train, he may select a green 
one. 
A profound understanding of this curious defect 
of color-perception must be acquired to enable the 
surgical expert to make the best use of these various 
methods, and whilst they are sufficient they are de- 
cisive and require but little time. Perhaps the 
transcript of one case from my record-book may 
illustrate these brief descriptions : 
J. H., employed by the Pennsylvania Railroad 
Co., forty three years old; found defective, and 
referred for final opinion. 
Color-stick: With green, selects Nos. i, 2, 3, 4, 
6, 7, 11, 13, 15, 17 ; with rose, selects Nos. 22, 25, 
21, 27, 28 ; with red, selects Nos. 31, 32, 33, 34, 37. 
Holmgren: Green, selects 2 greens and 21 con- 
fusions; rose, selects 5 greens, with 13 confusions; 
red, selects 8 greens, with 9 confusions, 2 greens. 
Bonders: Fails at 5 m. on all apertures; fails at 
1 m. on all apertures; x/i m. on all apertures. 
Calls, with 20 mm. opening, green red ; red green, 
and white, light-red. 11 
He made more mistakes than successes, with gray 
(London-smoke glass) over white; called it red and 
green, as light was increased or diminished, and 
finally declared that he had never seen such lights 
on a railroad. 
Failed with switchlight, 4 inches in diameter, at 
5 m. and at 1 m., and manifested a color-blindness 
or defect greater than -gfo, as he failed to see at 
1 m. what a normal eye would recognize infallibly 
at 500 meters. 
Cobalt-glass: Sees white light with blue halo; no 
red or rose. 
Flags: At 1 m. calls dirty-white green ; fails to 
distinguish red from green. He was then told to 
select from a pile of flags the danger-signal, or red 
one, and to hurry back and protect his train ; with 
his own hands and deliberately he chose six—three 
red, two green, and one blue—stating that “ they 
would all stop trains.” 
Stilling’s tables: Fails in all but VII, which 
should be recognized by a color-blind. 
Pronounced color-blind and unfit for any duty 
in which he would govern his actions with color- 
signals. 
I will conclude by urging the need for reexami- 
nations at stated periods, and in individual cases 
when a man has been injured, or has recovered from 
a serious illness, or when he uses tobacco or alcohol 
to excess. 
The test here described can be obtained of Queen 
6 Co., of Philadelphia. The Medical News. 
Established in 1843. 
A WEEKL YMEDICAL NEWSPAPER. 
Subscription, $4.00per Annum. 
The American yournal 
OF THE 
Medical Sciences. 
Established in 1820 
A MONTHLY MEDICAL MAGAZINE. 
Subscription, $4.00 per Annum. 
COMMUTA TION RA TE, 50 PER ANNUM. 
LEA BROTHERS & CO. 
PHILADELPHIA.