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Hyperlinks have been added to assist the reader navigate the +book.</p> +</div> + + +<div class="tac fs160 ws02">THE HUNTERIAN LECTURES</div> + +<div class="tac fs80 mtb1em">ON</div> + +<div class="tac fs120 mb5em ws02">COLOUR-VISION AND COLOUR-BLINDNESS</div> + +<div class="titlepage"> +<h1><span class="t1">THE</span> + +<span class="t2">HUNTERIAN LECTURES</span> + +<span class="t3">ON</span> + +<span class="t4">COLOUR-VISION AND<br> +COLOUR-BLINDNESS</span></h1> + + +<div class="tp1"><i>Delivered before the Royal College of Surgeons of England<br> +on February 1st and 3rd, 1911</i></div> + + +<div class="tp2">BY</div> + +<div class="tp3">PROFESSOR F. W. EDRIDGE-GREEN</div> + +<div class="tp4"><span class="smcap">M.D.Durh., F.R.C.S.Eng.</span></div> + +<div class="tp4"><span class="lowercase smcap">BEIT MEDICAL RESEARCH FELLOW</span></div> + + +<div class="tp5">KEGAN PAUL, TRENCH, TRÜBNER <i>&</i> <span class="smcap">Co., Ltd.</span></div> +<div class="tp6">43 GERRARD STREET, LONDON, W.</div> +<div class="tp7">1911</div> +</div> + +<hr class="chap x-ebookmaker-drop"> + +<p><span class="pagenum" id="Page_5">5</span></p> + + +<div class="chapter"> +<h2 class="nobreak" id="PREFACE">PREFACE</h2> +</div> + + +<p>As there are many who are interested in the +subject of vision and colour-blindness who are +not acquainted with the structure of the eye, I will +give a few details so that these persons may be +able to consider the problem from the point of +view of these lectures.</p> + +<p>The eye is very similar to a photographic camera, +and an actual image is formed on the back of the +eye just as it is on the plate of the photographic +camera or on the view-finder. The eye possesses +a lens and also an iris which acts as an adjustable +stop and regulates the size of the pupil. The +membrane at the back of the eye upon which the +image is formed is called the retina. The retina +has several layers, but the sensitive layer consists +of two elements called, from their shape, rods and +cones. The problem therefore which has to be +considered is, how is the light which forms the +image on the sensitive layer of the retina transformed +into visual impulses?</p> + +<p>Those who are interested in the subject will +find further details in my book on <i>Colour-Blindness<span class="pagenum" id="Page_6">6</span> +and Colour-Perception</i> in the International Scientific +Series. In that book there are three plates +which show how the colour-blind see colours.</p> + +<p>I have been annoyed to find that unauthorised +persons have made lanterns professing to be mine +but grossly inaccurate. The sole makers are those +mentioned on page 53 in this book.</p> + +<p class="tar mr1em"> +<span class="smcap">F. W. Edridge-Green.</span></p> + +<p><span class="smcap">The Institute of Physiology,<br> +  University College,<br> +    Gower Street, London.</span></p> + +<hr class="chap x-ebookmaker-drop"> + +<div class="chapter"> +<p><span class="pagenum" id="Page_7">7</span></p> + +<h2 class="nobreak" id="CONTENTS">CONTENTS</h2> +</div> + +<div class="center"> +<table id="toc" class=""> +<tr> +<td class="tac fs120" colspan="3"><div>LECTURE I</div></td> +</tr> +<tr> +<td class="tac fs110 pt05" colspan="3"><div>THE THEORY AND FACTS OF COLOUR-VISION<br>AND COLOUR-BLINDNESS</div></td> +</tr> +<tr> +<td class="tar fs70" colspan="3"><div>PAGE</div></td> +</tr> +<tr> +<td style="text-align: left; text-indent: -2em;" class="fs110" colspan="2"><span class="smcap">The Visual Purple the Essential Factor in Vision</span></td> +<td class="tar"><div><a href="#Page_11">11</a></div></td> +</tr> +<tr> +<td class="tar"><div> 1.</div></td> +<td class="tal">Anatomical Evidence</td> +<td class="tar"><div><a href="#Page_11">11</a></div></td> +</tr> +<tr> +<td class="tar"><div> 2.</div></td> +<td class="tal">Physiological Analogy with other Body Cells</td> +<td class="tar"><div><a href="#Page_12">12</a></div></td> +</tr> +<tr> +<td class="tar"><div> 3.</div></td> +<td class="tal">The Relation between the Foveal and the Extra-Foveal Regions</td> +<td class="tar"><div><a href="#Page_13">13</a></div></td> +</tr> +<tr> +<td class="tar"><div> 4.</div></td> +<td class="tal">The varying Sensibility of the Fovea</td> +<td class="tar"><div><a href="#Page_13">13</a></div></td> +</tr> +<tr> +<td class="tar"><div> 5.</div></td> +<td class="tal">Chemical Analogy</td> +<td class="tar"><div><a href="#Page_14">14</a></div></td> +</tr> +<tr> +<td class="tar"><div> 6.</div></td> +<td class="tal">Disappearance of Lights falling upon Fovea</td> +<td class="tar"><div><a href="#Page_15">15</a></div></td> +</tr> +<tr> +<td class="tar"><div> 7.</div></td> +<td class="tal">Illusion of Moving Light</td> +<td class="tar"><div><a href="#Page_16">16</a></div></td> +</tr> +<tr> +<td class="tar"><div> 8.</div></td> +<td class="tal">Purple After-Image</td> +<td class="tar"><div><a href="#Page_17">17</a></div></td> +</tr> +<tr> +<td class="tar"><div> 9.</div></td> +<td class="tal">Currents seen in the Field of Vision not due to the Circulation</td> +<td class="tar"><div><a href="#Page_17">17</a></div></td> +</tr> +<tr> +<td class="tar"><div>10.</div></td> +<td class="tal">Pressure Figure</td> +<td class="tar"><div><a href="#Page_19">19</a></div></td> +</tr> +<tr> +<td class="tar"><div>11.</div></td> +<td class="tal">Macular Star</td> +<td class="tar"><div><a href="#Page_19">19</a></div></td> +</tr> +<tr> +<td class="tar"><div>12.</div></td> +<td class="tal">Entoptic Appearance of Cone Mosaic</td> +<td class="tar"><div><a href="#Page_20">20</a></div></td> +</tr> +<tr> +<td class="tar"><div>13.</div></td> +<td class="tal">Visual Acuity</td> +<td class="tar"><div><a href="#Page_21">21</a></div></td> +</tr> +<tr> +<td style="text-align: left; text-indent: -2em;" class="fs110" colspan="2"><span class="smcap">The Evolution of the Colour-Sense</span></td> +<td class="tar"><div><a href="#Page_26">26</a></div></td> +</tr> +<tr> +<td style="text-align: left; text-indent: -2em;" class="fs110" colspan="2"><span class="smcap">The Facts of Colour-Blindness</span></td> +<td class="tar"><div><a href="#Page_34">34</a></div></td> +</tr> +<tr> +<td class="tar"><div> 1.</div></td> +<td class="tal">Defects of Light-Perception</td> +<td class="tar"><div><a href="#Page_35">35</a></div></td> +</tr> +<tr> +<td class="tar"><div> 2.</div></td> +<td class="tal">Defects of Colour-Perception</td> +<td class="tar"><div><a href="#Page_38">38</a></div></td> +</tr> +<tr> +<td style="text-align: left; text-indent: -2em;" class="fs110" colspan="2"><span class="smcap">The Two Main Varieties of Colour-Blindness</span>:</td> +<td></td> +</tr> +<tr> +<td class="tar"><div> 1.</div></td> +<td class="tal">Dichromic Vision</td> +<td class="tar"><div><a href="#Page_40">40</a></div></td> +</tr> +<tr> +<td class="tar"><div> 2.</div></td> +<td class="tal">Trichromic Vision</td> +<td class="tar"><div><a href="#Page_42">42</a></div><span class="pagenum" id="Page_8">8</span></td> +</tr> +<tr> +<td class="tac fs120" colspan="3"><div>LECTURE II</div></td> +</tr> +<tr> +<td class="tac fs110 pt05" colspan="3"><div>THE DETECTION OF COLOUR-BLINDNESS FROM A<br>PRACTICAL POINT OF VIEW</div></td> +</tr> +<tr> +<td class="tar"><div> 1.</div></td> +<td class="tal">Object of a Test for Colour-Blindness</td> +<td class="tar"><div><a href="#Page_44">44</a></div></td> +</tr> +<tr> +<td class="tar"><div> 2.</div></td> +<td class="tal">The Requirements of a Test for Colour-Blindness</td> +<td class="tar"><div><a href="#Page_45">45</a></div></td> +</tr> +<tr> +<td class="tar"><div> 3.</div></td> +<td class="tal">Persons to be Excluded</td> +<td class="tar"><div><a href="#Page_47">47</a></div></td> +</tr> +<tr> +<td class="tar"><div> 4.</div></td> +<td class="tal">The Construction of a Test for Colour-Blindness</td> +<td class="tar"><div><a href="#Page_48">48</a></div></td> +</tr> +<tr> +<td class="tar"><div> 5.</div></td> +<td class="tal">The Lantern Test</td> +<td class="tar"><div><a href="#Page_53">53</a></div></td> +</tr> +<tr> +<td class="tar"><div> 6.</div></td> +<td class="tal">Other Tests for Colour-Blindness</td> +<td class="tar"><div><a href="#Page_66">66</a></div></td> +</tr> +</table> +</div> + +<hr class="chap x-ebookmaker-drop"> + +<p><span class="pagenum" id="Page_9">9</span></p> + +<p class="tac fs130">LECTURE I</p> + +<p class="tac ptb05"><i>Delivered on February 1st</i></p> + + +<p><span class="smcap">Gentlemen</span>,—Colour-blindness is not a good name +for the condition to which it is applied, and still +worse is the use of the term red-blindness or green-blindness. +In the majority of cases of colour-blindness +there is no blindness to colours in the +ordinary acceptation of the term; a green, red, or +yellow light produces a very definite sensation of +colour. Those who confuse red and green do so, +not because they see red as green or green as red, +but because both give rise to a similar sensation of +colour. The word light must be used in the sense +of referring to those waves which excite the organ +of vision. Because two stimuli excite a sensation +of light, it does not follow that they are similar. +We cannot, for instance, distinguish by the eye +polarised light from non-polarised light. We have +to distinguish between the physical stimuli by +their physical properties apart from their effect on +the organ of vision. I propose to divide the +subject into two parts, and in this lecture to deal +with the theory and facts of colour-vision and +colour-blindness, and in the second lecture with +the detection of colour-blindness from a practical +point of view.</p> + +<hr class="r15 x-ebookmaker-drop"> + +<div class="chapter"> +<p><span class="pagenum" id="Page_10">10</span></p> + +<h2 class="nobreak" id="I_The_Theory_and_Facts_of_Colour-Vision">I. <span class="smcap">The Theory and Facts of Colour-Vision +and Colour-Blindness</span></h2> +</div> + + +<p>The following is the theory which I have propounded +in order to explain vision and colour-vision. +A ray of light impinging on the retina +liberates the visual purple from the rods and a +photograph is formed. The rods are concerned +only with the formation and distribution of the +visual purple, not with the conveyance of light-impulses +to the brain. The ends of the cones are +stimulated through the photo-chemical decomposition +of the visual purple by light (very +probably through the electricity which is produced), +and a visual impulse is set up which is +conveyed through the optic-nerve fibres to the +brain. The character of the stimulus differs +according to the wave-length of the light causing +it. In the impulse itself we have the physiological +basis of the sensation of light, and in the quality +of the impulse the physiological basis of the +sensation of colour. The impulse being conveyed +along the optic nerve to the brain, stimulates the +visual centre, causing a sensation of light, and +then passing on to the colour-perceiving centre, +causes a sensation of colour. But though the +impulses vary in character according to the wave-length +of the light causing them, the retino-cerebral +apparatus is not able to discriminate +between the character of adjacent stimuli, not +being sufficiently developed for the purpose. At +most, seven distinct colours are seen, whilst +others see in proportion to the development of<span class="pagenum" id="Page_11">11</span> +their colour-perceiving centres, only six, five, +four, three, or two. This causes colour-blindness, +the person seeing only two or three colours instead +of the normal six, putting colours together as +alike which are seen by the normal-sighted to be +different. In the degree of colour-blindness just +preceding total, only the colours at the extremes +of the spectrum are recognised as different, the remainder +of the spectrum appearing grey. Though +my own opinion is that the ordinary form of congenital +colour-blindness is caused by a defective +development of the portion of the brain which has +the function of the perception of colour, we must +not exclude any portion of the retino-cerebral apparatus, +defect of which would have exactly the +same result. It will be noticed that the theory +really consists of two parts, one concerned with +the retina and the other with the whole retino-cerebral +apparatus. I shall in these lectures use +the word cerebral in this sense. I am not aware +of a single fact which does not support this theory, +and I have used it to predict facts which have +subsequently been rediscovered by others and +now form a part of our common knowledge.</p> + + +<h3>THE VISUAL PURPLE THE ESSENTIAL FACTOR +IN VISION</h3> + +<p>I will now state very briefly the evidence which +supports the view that the visual purple is the +essential factor in the retina which enables it to +transform light into visual impulses.</p> + +<p>1. <i>Anatomical.</i>—In the fovea of the retina only +cones are to be found. Immediately external to<span class="pagenum" id="Page_12">12</span> +this each cone is surrounded by a ring of rods. +The number of rings of rods round each cone +increases as the periphery is reached. The outer +segments of the cones are situated in a space +which is filled with fluid. The external limiting +membrane retains this fluid in its place. I find<a id="FNanchor_1" href="#Footnote_1" class="fnanchor">1</a> +four depressions or canals which lead into the +larger depression of the external fovea. These +canals appear to have smaller branches, and serve +to conduct the visual purple into the part of most +acute vision. The cones which are present in the +fovea have very long outer segments which would +present a greater surface for photo-chemical +stimulation. The visual purple is only to be found +in the rods and not in the cones. I determined to +ascertain whether the visual purple could be seen +between the cones in the fovea. I have examined +under the microscope the retinas of two monkeys +which had been kept previously in a dark room for +forty-eight hours. The yellow spot was the +reddest part of the whole retina, and the visual +purple was seen to be between and not in the +cones.<a id="FNanchor_2" href="#Footnote_2" class="fnanchor">2</a></p> + +<p>2. <i>Physiological analogy with other body cells.</i>—It +is far more probable that the rods should produce +a secretion which would affect other cells +rather than themselves. The liver cells do not +form bile in order to stimulate themselves, and the +internal secretions are produced to affect other +parts of the body. I am not aware of a single +instance in which a cell produces a secretion which<span class="pagenum" id="Page_13">13</span> +has the function of stimulating the cell producing +it. The visual purple is regenerated in the rods by +the pigment cells in connection with them.</p> + +<p>3. <i>The relation between the foveal and the extra-foveal +regions.</i>—As the fovea only contains cones, +if any of the older theories of the relative functions +of the rods and cones were true we should expect +to find qualitative differences between the foveal +and extra-foveal regions. This is not the case, +but as we should expect if the visual purple were +the visual substance, all the phenomena which +have been attributed to the visual purple should +be found in the fovea. Von Tschermak, Hering, +Hess, Garten and others have found the Purkinje +phenomenon, the variation in optical white equations +by a state of light and dark adaptation, the +colourless interval for spectral lights of increasing +intensity, and the varying phases of the after-image +in the fovea only gradually diminished.</p> + +<p>4. <i>The varying sensibility of the fovea.</i>—The +fovea is in some conditions the most sensitive part +of the whole retina, and with other conditions the +least. Helmholtz has recorded some of these facts +and regarded them as quite inexplicable. We have, +however, an easy explanation of the facts on the +assumption that when there is visual purple in the +fovea this is the most sensitive part of the whole +retina, but when there is none there time must +elapse before it can diffuse into the spot, and in +the meantime it is insensitive to light. I have +devised several experiments which show the +visual purple flowing into the foveal region. The +following simple experiment shows this very well.<span class="pagenum" id="Page_14">14</span> +If on awaking in the morning the eyes be directed +to a dull white surface, as for instance the ceiling, +the region of the yellow spot will appear as an +irregular black spot, and light will appear to invade +this spot from without inwards. If the eyes be +now closed and covered with the hands, purple +circles will form round the centre of the field of +vision and gradually contracting reach the centre. +When the circle reaches the centre it breaks up +into a star-shaped figure and becomes much +brighter. It then disappears and is followed by +another contracting circle. Now it will be noticed +that if one eye be opened when the circle has +broken up, a brilliant rose-coloured star much +brighter than any other part will be seen in the +centre of the field of vision. This has the exact +hue of the visual purple. If we wait until the +star has disappeared before opening an eye, the +macular region appears as a black spot as before. +This conclusively shows that the central portion +of the retina is sensitised from the peripheral +portions.</p> + +<p>5. <i>Chemical analogy.</i>—The visual purple gives +a curve which is very similar to that of many other +photo-chemical substances. We know that with +photo-chemical substances the chemical effect is +not proportional to the intensity of the light. That +is, a different curve is obtained with weak light from +that which is formed with light of greater intensity. +It is reasonable, therefore, to suppose that the +visual purple which is formed by the pigment +cells under the influence of a bright light would be +somewhat different in character from that which is<span class="pagenum" id="Page_15">15</span> +formed in darkness. Again, from the chemical +analogy which I have just given, even if the +visual purple were of the same character, we +should not expect similar curves with different +intensities of light. It is probable that both +factors are in operation. This deduction gives an +explanation of the Purkinje phenomenon, or the +fact that when the eyes are adapted to darkness +the point of greatest luminosity is shifted more +towards the violet end of the spectrum. Some +dichromics who have shortening of the red end of +the spectrum have a luminosity curve which is very +similar to that of a normal-sighted person with +a spectrum of lesser intensity. We have only to +assume in these cases either that the receiving +nervous apparatus is less responsive, or that the +visual purple formed at one intensity of light is +similar to that formed at a lower intensity by a +normal-sighted person. We also have an explanation +of other conditions, such as erythropsia, or +red vision, white objects appearing more or less +red. If we suppose that the eye has remained +in a state of light adaptation, the visual purple +produced being more sensitive to the red rays, +objects appear of this colour. As we should +expect, erythropsia is frequently associated with +hemeralopia, or difficulty in seeing in the twilight, +the eyes being adapted to light and not to darkness. +In green vision the eyes have probably +remained in a condition of more or less adaptation +to darkness, and are therefore more sensitive +to the green rays.</p> + +<p>6. <i>Disappearance of lights falling upon fovea.</i>—If<span class="pagenum" id="Page_16">16</span> +the cones are not sensitive to light, a ray of +light falling upon the fovea alone and not upon +the adjacent portion of the retina containing rods +should produce no sensation of light, provided that +there is not already any visual purple in the fovea. +It has been known to astronomers for a long time +that if a small star in a dark portion of the sky be +steadfastly looked at, it will disappear from view, +whilst other stars seen by indirect vision remain +conspicuously visible. The following simple experiment +shows the same thing. If a piece of black +velvet about three feet square on a door have a pin +put in the centre, and the source of light be behind +the observer, the pin will be brightly illuminated; +and on looking at it (the observer not being too +close) and keeping the eye quite still, the pin will +disappear, the visual substance diffused into the +fovea centralis being used up and not renewed. +When viewed by indirect vision it is impossible to +make it disappear in this way. When I have +taken great care to have very dark surroundings +and have used only one eye, I have made moderately +bright lights disappear in this manner. +These facts have been attributed to a defective +sensibility of the fovea for feeble light. The +important point, however, that the light is at first +most clearly seen by the fovea and only subsequently +fades, has been overlooked. If these facts +were due to a defective sensibility of the fovea, the +star or light would not be visible at first.</p> + +<p>7. <i>Illusion of moving light.</i>—If a small light be +looked at fixedly in a dark room, it will appear +to move until it comes apparently so close that<span class="pagenum" id="Page_17">17</span> +it could be grasped. The reason of this is that +the eye moves so that the light falls upon a more +peripheral part of the retina. I find that the +movement takes place as if some photo-chemical +substance acted under the influence of gravity. +For instance, when standing the light appears to +travel upwards; resting the head on one side, it +appears to travel in the opposite direction. The +light appears as if we were looking straight at it, +and the eye, which is covered up, remains directed +straight at the object. When the second eye is +opened two images of the light are seen, and the +image which is seen with the periphery of the +first eye rapidly coalesces with that seen directly +by the second eye.</p> + +<p>8. <i>Purple after-image.</i>—A positive after-image +of a purple (rose) colour can be obtained after +white light or any spectral colour. It will be +noticed that when there is little light during the +subsequent observation the colour of an after-image +inclines to blue or green, when there is +more light towards purple or red.</p> + +<figure class="figcenter illowe25_625" id="i_18"> + <img class="w100" src="images/i_18.jpg" alt=""> + <figcaption><p>Fig. 1.</p></figcaption> +</figure> + +<p>9. <i>Currents seen in the field of vision not due to +the circulation.</i>—It occurred to me that if there +were canals in the retina which promoted the easy +flow of the visual purple into the fovea, we ought +to obtain evidence of the currents flowing along +these channels entoptically. I found that this +was the case, and that the currents could be seen +in numerous ways.<a id="FNanchor_3" href="#Footnote_3" class="fnanchor">3</a> If one eye be partially +covered with an opaque disc whilst both eyes +are directed forwards in a not too brightly illuminated<span class="pagenum" id="Page_18">18</span> +room, and special attention be paid to the +covered eye, an appearance of whirling currents +will be seen with this eye (see Fig. 1). These +currents appear to be directed towards the centre, +and have a very similar appearance to a whirlpool +which is fed by four main branches. These<span class="pagenum" id="Page_19">19</span> +again are fed by smaller branches which continually +change their paths. On closing both +eyes all the portion in which the whirling currents +are seen appears as dull purple. These +currents cannot be due to vessels, because we +know that the centre of the retina corresponding +to the point where the greatest movement is seen +is free from vessels. The appearance is also very +different from that of the movement of blood in +vessels. The currents can also be seen in the +light, in the dark, through yellow-green glass, and +with intermittent light. The main branches form +a star-shaped figure with four rays. The currents +carry the visual quality, colour, and brightness +from whence they come into an after-image. +They also tend to move an after-image towards +the centre. The currents behave as if they ran +in definite channels, but could also overrun, on +any further stimulus, the banks of the channels. +For instance, a thin, bright line with a little more +light appears as a broad band, and the central +star figure will enlarge into a rhomboid, oval or +disc. Movements of the eyes affect the broad +currents in the outer part of the field of vision.</p> + +<p>10. <i>Pressure figure.</i>—Pressure on the front of +the eye causes the star-shaped figure to be seen, +and this changes into a rhomboid with a little +more pressure.</p> + +<p>11. <i>Macular star.</i>—It occurred to me that we +ought to obtain evidence of the canals in the +retina in cases where the outflow from the retina +is obstructed, as by tumour. I find this is the +case; the star-shaped figure given by Sir Victor<span class="pagenum" id="Page_20">20</span> +Horsley in his paper on tumour of the frontal lobe<a id="FNanchor_4" href="#Footnote_4" class="fnanchor">4</a> +is almost exactly the same as that seen subjectively.</p> + +<figure class="figcenter illowe27_5" id="i_20"> + <img class="w100" src="images/i_20.jpg" alt=""> + <figcaption><p>Fig. 2.</p></figcaption> +</figure> + +<p>12. <i>Entoptic appearance of cone mosaic.</i>—Appearances +corresponding to the cone mosaic of +the retina may be seen in several ways<a id="FNanchor_5" href="#Footnote_5" class="fnanchor">5</a> (see +Fig. 2). The appearance seen corresponds to the<span class="pagenum" id="Page_21">21</span> +cone distribution of the retina as viewed from its +outer side, the portions occupied by rods appearing +as dark spaces.</p> + +<p>13. <i>Visual acuity.</i>—Visual acuity is most acute +with the fovea, and diminishes from within outwards. +It corresponds very fairly with the cone +distribution of the retina. On the other hand, +there is not one single fact which points to the +rods as being light-sentient organs. This is well +recognised by those best qualified to judge.<a id="FNanchor_6" href="#Footnote_6" class="fnanchor">6</a> I +could give many more facts in support of the +view that the visual purple is the visual substance, +and I have not yet had brought to my notice +any fact which is not readily explicable on that +hypothesis. There may be other photo-chemical +substances in the retina, but there is not the +slightest evidence that such is the case. I regard +the visual purple as the sole visual substance. +We could, of course, split the visual purple into +innumerable simpler photo-chemical substances, +each of which has its own absorption curve, +having its maximum in some particular part of +the spectrum. It is difficult to say at present +exactly how the visual purple acts as a stimulus +transformer, but this is because so many plausible +hypotheses immediately occur to us. It is very +probable that light acting upon the visual purple +is, according to its wave-length, absorbed by particular +atoms or molecules, the amplitude of their +vibrations being increased. These vibrations may +cause corresponding vibrations in certain discs of +the outer segments of the cones, which seem<span class="pagenum" id="Page_22">22</span> +especially constructed to take up vibrations. We +know that when light falls on the retina it causes +an electric current. We know how the telephone +is able through electricity to convey waves of +sound, and something similar may be present +in the eye, the apparatus being especially constructed +for vibrations of small wave-length. +The current of electricity set up by light may +cause the sensation of light, and the vibrations of +the atoms or molecules the sensation of colour.</p> + +<p>In all vital processes there is a condition of +katabolism or chemical change in the protoplasm, +and an anabolic or building-up process, in which +the protoplasm is restored to its normal state. +We have therefore to consider two definite processes +in the visual purple—namely, a breaking +down of the visual purple photo-chemically by +light and its restoration by the pigment cells and +rods. Under ordinary conditions of light, and +during the whole of the daytime, the visual purple +is continually being bleached and reformed. It +is obvious, therefore, that when the eye has been +kept in the dark and is then exposed to light, an +observation taken immediately will not be comparable +with one taken a few seconds afterwards, +because in the first observation we have only to +consider the katabolic change; whilst in the +second observation the anabolic change has to be +considered as well, as the visual purple has to be +reformed for subsequent seeing. There appears +to be very little evidence in ordinary circumstances +of this anabolic process; for instance, if we +fatigue the eye with sodium light in a dark room,<span class="pagenum" id="Page_23">23</span> +and then immediately examine a spectrum, we +find that though all the yellow has disappeared +there is no increase in the blue; in fact, the blue +seems rather diminished than otherwise. Again, +there is not the slightest diminution in either the +red or green, showing conclusively that yellow +cannot be a compound sensation made up by a +combination of red and green. We must therefore +explain in another way the apparent trichromatism +of normal colour-vision, which is so +well known to every photographer, especially +those who are concerned with colour photography. +If my theory of the evolution of the +colour-sense be the correct one, and we have +cases of colour-blindness corresponding to every +degree of the evolutionary process, we have an +explanation of the facts. In past ages all saw +the rainbow made up of only three colours—red, +green, and violet. When a new colour (yellow) +appeared between the red and green, it is obvious +that a mixture of red and green would give rise, +not to red-green, but to the colour which had replaced +it—namely, yellow. The retina, therefore, +corresponds to a layer of photo-chemical +liquid in which there are innumerable wires each +connected with a galvanometer. When light falls +upon a portion of this fluid the needle of the +galvanometer corresponding to the nearest wire +is deflected. The wires correspond to the separate +fibres of the optic nerve, and the galvanometers +to the visual centres of the brain.</p> + +<p>Cases of colour-blindness may be divided into +two classes, which are quite separate and distinct<span class="pagenum" id="Page_24">24</span> +from each other, though both may be present in +the same person. In the first class there is light +as well as colour loss. In the second class the +perception of light is the same as the normal-sighted, +but there is a defect in the perception +of colour. In the first class certain rays are either +not perceived at all or very imperfectly. Both +these classes are represented by analogous conditions +in the perception of sounds. The first +class of the colour-blind is represented by those +who are unable to hear very high or very low +notes. The second class of the colour-blind is +represented by those who possess what is commonly +called a defective musical ear. Colour-blind +individuals belonging to this class can be +arranged in a series. At one end of this series +are the normal-sighted, and at the other end the +totally colour-blind. The colours appear at the +points of greatest difference, and I have classified +the colour-blind in accordance with the number +of colours which they see in the spectrum. The +normal-sighted may be designated hexachromic; +those who see five colours, pentachromic; those +who see four, tetrachromic; those who see three, +trichromic; those who see two, dichromic; and +those who see none, totally colour-blind. There +are many degrees included in the dichromic class. +There may or may not be a neutral band, and this +is widest in those cases approaching most nearly +to total colour-blindness. I have recorded a case +of a patient who was colour-blind with one eye.<span class="pagenum" id="Page_25">25</span><a id="FNanchor_7" href="#Footnote_7" class="fnanchor">7</a> +It is an interesting fact that for form vision the +colour-blind eye was much the better of the two, +and he could recognise fine lines in the spectrum +with this eye which were not visible to the other. +He saw the two ends of the spectrum tinged with +colour and the remainder grey. It will be noticed +that his colour sensations were limited to the extreme +red and the extreme violet—namely, those +colours which present the greatest physical contrast +to each other. Neither the red nor the +violet appeared of the nature of a primary colour, +but gave the impression that they were largely +diluted with grey. A theory of colour-vision +must account for a case of this kind, and also for +the other varieties and degrees of colour-blindness. +The trichromic are a very important class, and +any theory must account for the fact that they +see yellow as red-green, and blue as violet-green. +As we should theoretically expect, when there is +shortening of the spectrum the centres of the +colours are moved towards the unshortened side.</p> + +<p>I will now show on the screen some representations +of pictures painted by colour-blind persons. +The upper picture is the copy, and the one below +is the one which has been painted by the colour-blind +artist. He has been given a selection of +colours on plates, and from them has selected the +one which he thought appropriate in each case. +It will be noticed that the mistakes made are +characteristic of the colour-perception of the +person painting them. Whenever I show these +pictures, I am asked why it is that these characteristic +mistakes should be made, and that<span class="pagenum" id="Page_26">26</span> +the true colour of the object is not used instead? +This undoubtedly would be the case if the artist +were allowed to match the colours by directly +comparing them. But he is not able to do this; +he looks at the copy and decides upon the colour +of an object, and then looks for the colour with +which to paint it.</p> + +<p>A man rarely uses a hue which he does not see +as a definite colour, and therefore it has been +quite possible for me to pick out those who are +more or less colour-blind in the exhibitors of the +picture gallery. For instance, if a trichromic have +to paint a yellow object he will decide, after looking +at it, whether it be a red or green in his estimation, +and represent it accordingly. He will be +greatly influenced by the nature of colours in its +immediate proximity, because simultaneous contrast +is increased in the colour-blind. Thus he +will certainly represent a yellow which is adjacent +to a red as green, and a yellow which is adjacent +to a green as red.</p> + + +<h3>THE EVOLUTION OF THE COLOUR-SENSE</h3> + +<p>There can be no doubt that an evolution of the +colour-sense has taken place: the only point is +how and when did this occur. It is obvious that +in those low forms of animal life in which the most +rudimentary sense of sight exists there can be +no sense of colour. The animal which can only +perceive light and shade can only discriminate in +a rough way between varying intensities of the +stimulus. It is obvious, therefore, that the sense of +light must have been developed first and then the<span class="pagenum" id="Page_27">27</span> +sense of colour. The sense of sight must have been +first developed for those waves which produce their +maximum effect upon the sensitive protoplasm. +The next process of development would be for the +protoplasm to become sensitive to the waves above +and below those which produced the primary +stimulus. In the physical stimulus which produces +the sensation of light there are two factors +to be considered, the length of the wave and its +amplitude: the greater the amplitude within +certain limits the greater the intensity of the +sensation. The wave-length of the physical +stimulus is the physical basis of the sensation of +colour. How did the sensations of colour first +arise? Let us suppose that the physiological +effect of the physical stimulus differed according +to the wave-length of the physical stimulus.</p> + +<p>Let us consider that the eye has reached a stage +in which it has become sensitive to a fair range of +the spectral rays; that is to say, evolution has +proceeded to the extent of making the protoplasm +sensitive to rays of light considerably above and +below those which first caused a sensation of +light. We now have an eye which is sensitive +to the greater part of the rays which form the +visible spectrum. It is, however, an eye which is +devoid of the sense of colour; no matter from +what part of the spectrum the rays be taken the +only difference which will be appreciated will be +one of intensity. I however mentioned that in the +physical stimulus there were two variables, wave-length +and amplitude of the wave. Let us now +suppose that a fresh power of discrimination was<span class="pagenum" id="Page_28">28</span> +added to the eye and that it became able to discriminate +between different wave-lengths of light. +What would be the most probable commencement +of development of the sense of colour? Undoubtedly +to my mind the differentiation of +physical stimuli which were physically most +different. That is to say, the eye would first +discriminate between the rays which are physically +most different in the visible spectrum, the +red and the violet, that is presuming the eye had +become sensitive to this range. It is probable +that it had not, and there has been a steady +evolution as to the extent of the spectrum perceived +as well as to colour. We have examples of +this in those cases of defective light-perception +in which there is shortening of the red or violet +end of the spectrum.</p> + +<p>Let us now work out the evolution of the colour-sense +on the assumption that the rays which are +physically most different, namely, red and violet, +were those which were first differentiated. We +know that the various rays differ in their effects on +various substances; the red rays are more powerful +in their heating effects, whilst the violet rays are +more active actinally, as is well known by the +readiness with which they act upon a photographic +plate, which is scarcely affected by red light. We +should now have an individual who would see the +spectrum nearly all a uniform grey of different +degrees of luminosity, but with a tinge of red at +one end and a tinge of violet at the other. There +is a great deal of evidence to show that this is how +the colour-sense was first developed. For instance,<span class="pagenum" id="Page_29">29</span> +in the degree of colour-blindness just preceding +total the spectrum is seen in this way. I have also +examined a woman who became totally colour-blind, +apparently through disease of the ear. I +examined her when she had recovered a certain +amount of colour sensation; her sensations were +confined to the extreme red and violet. As the +colour sense developed it was not necessary that +the rays should differ so much in refrangibility +before a difference was seen, and so the red and +violet gradually invaded the grey or neutral band, +until at a certain point they met in the centre of +the spectrum. Such cases are called dichromics.</p> + +<p>The next stage of evolution of the colour-sense +is when the colour-perceiving centre is sufficiently +developed to distinguish three main colours in the +spectrum. The third colour, green, appears in the +centre of the spectrum, that is, at the third point +of the greatest physiological difference. In +accordance with the prediction of the theory, I +found a considerable number of persons who saw +the spectrum in this way, about 1·5 per cent of +men. The trichromic see three main colours in +the spectrum—red, green, and violet. They usually +describe the spectrum as consisting of red, red-green, +green, green-violet, and violet. They do +not see yellow and blue as distinct colours, and are +therefore in continual difficulty over them. There +are very few of the tests in general use which can +detect them, especially if names be not used. +They will usually pass a matching test with ease. +An examination with the spectrum shows that +their colour-perception is less than the normal in<span class="pagenum" id="Page_30">30</span> +every part, though the curve has the same general +shape. The three trichromics described in my +recent paper<a id="FNanchor_8" href="#Footnote_8" class="fnanchor">8</a> on “The Relation of Light-Perception +to Colour-Perception” each saw ten +consecutive monochromatic patches in the spectrum +instead of the eighteen or nineteen seen by +those who see six colours in the spectrum. It is +easy to show that the trichromic are dangerously +colour-blind. They will mark out with my colour-perception +spectrometer a patch containing +greenish yellow, yellow, and orange-yellow, and +declare that it is absolutely monochromatic. +When tested with coloured lights they find great +difficulty with yellow and blue. Yellow is continually +called red or green.</p> + +<p>There are several other degrees of colour +perception, and it may be well to say a word or +two about them, though I class all above the +trichromic with the normal-sighted for practical +purposes, as they are not dangerously colour-blind, +and can always, in ordinary circumstances, distinguish +signal lights correctly. In the next stage +of evolution four colours are seen in the spectrum, +and the fourth colour appears at the fourth point +of greatest physiological difference, namely, at +the orange-yellow of the hexachromic or six-colour +people. These persons I have designated “tetrachromic,” +because they see four distinct colours in +the spectrum, that is, red, yellow, green, and +violet. They do not see blue as a definite colour, +and are continually classing blues with greens; +they usually prefer to call blue, purplish green.<span class="pagenum" id="Page_31">31</span> +In the next stage of evolution there appeared +those who see five colours in the spectrum—red, +yellow, green, blue, and violet, blue being now +recognised as a definite colour. These are the +pentachromic group. These people pass all the +tests in general use with ease. They, however, +have a definitely diminished colour-perception +compared with the normal, or those who see six +colours in the spectrum. They mark out in the +spectrum only fifteen monochromatic patches +instead of eighteen. They cannot see orange as a +definite colour; for instance, they can never tell +whether a strontium light, which is red, or a +calcium light, which is orange, is being shown +them.</p> + +<p>In the next stage of evolution orange is recognised +as a definite colour, and thus we get the +hexachromic or normal group, and, as we should +theoretically expect, the yellow of the pentachromic +is now split up into two colours—orange +and yellow. The last stage of evolution which +we appear to have reached are those who see +seven colours in the spectrum, and the additional +one is called indigo. These constitute the heptachromic +group, and this seventh colour appears at +the exact point at which it should appear, according +to my theory, namely, between the blue and +violet. Persons belonging to this class have a +marvellous colour-perception and memory for +colours. They will indicate a certain shade of +colour in the spectrum, and then next day will be +able to put the pointer at precisely the same point, +a feat which is quite impossible to the ordinary<span class="pagenum" id="Page_32">32</span> +normal-sighted person. They see a greater +number of monochromatic patches in the spectrum +than the hexachromic, but the curve has the same +form. The marking out of the heptachromic does +not appear correct to those who see six colours; +for instance, the blue appears to invade the green, +and the indigo does not appear a definite colour +at all. If, however, we bisect the blue of the +seven-colour man, and then bisect his indigo, on +joining the centres we get the blue of the six-colour +man, showing most definitely that the blue +has been split up into two fresh colours. It will be +noticed that there is room for much further evolution, +and we could go on splitting up the spectrum +indefinitely if only we had the power to distinguish +these finer differences, but as a matter of +fact I have never met with a normal-eyed man +who could see more than twenty-nine monochromatic +patches in the spectrum, and there are +really millions, though by monochromatic patches +I do not mean twenty-nine separate colours. Not +only are all the details of the process of the evolution +of the colour-sense supported by all the facts +that we can obtain from literature and museums, +but the theory accounts for facts which were +previously inexplicable. The distinction between +light-sensation and colour-sensation is explained, +and all facts of colour-mixing, complementary +colours, and simultaneous contrast. We can +understand how, as in many cases which have been +recorded, a man may lose his colour-perception +and still have an unaltered sense of luminosity +and visual acuity.</p> + +<p><span class="pagenum" id="Page_33">33</span></p> + +<p>The explanation of complementary colours is a +fundamental part of the theory. It is obvious +that the two colours of the dichromic are only +recognised as different because they are seen in +contrast to each other, and that when they are +mixed they neutralise each other. It is the same +with the other colour-sensations, when they are +developed they replace the colours occupying +their positions. Therefore green which replaces +the grey of the dichromic should be, and is, +complementary to the other two colour-sensations, +red and violet combined. In the same way when +the yellow sensation replaces the red-green of the +trichromic it should be possible to compound it of +both. Also, when the green sensation is in a +feeble state of development it will not have the +value that it has at a subsequent stage, and, +therefore, yellow will be a much redder colour to +those persons than the normal, and in a colour +match of red and green forming yellow, more +green will be required.</p> + +<p>Simultaneous contrast is also explained. When +two colours are contrasted each appears to be a +colour higher or lower, as the case may be, in the +spectrum scale; that is to say, the close comparison +exaggerates the difference. As the colour-blind +have fewer colours, simultaneous contrast +should be greater with them, and this I have +found to be the case.</p> + +<p>There may be some relation between the monochromatic +patches and the discs in the outer segments +of the cones. These are about sixteen in +number in the guinea-pig. As in photography,<span class="pagenum" id="Page_34">34</span> +the intensity of the light is a very important factor +in vision. With colours of moderate intensity, +the periphery of the retina is found to be colour-blind, +but this apparent colour-blindness disappears +when more intense lights are used. A +person may have shortening of the spectrum with +light of moderate intensity, but when the light is +increased be able to recognise the spectrum to its +normal limit. The change in steepness of gradation, +according to the intensity of the light, is +well known to photographers. The Purkinje +effect, a change in maximum sensitiveness of the +eye according to the intensity of the light, is, in +my opinion, a photo-chemical effect. I find that +the Purkinje effect is found for small portions of +the retina if a black object has been situated in the +corresponding part of the field of vision. The +yellow pigment which is found in the yellow spot +probably acts like the yellow screen in photography, +which, by absorbing the blue and violet +rays of the atmosphere, renders visible that which +would otherwise be invisible. This is further +borne out by the fact that hunters in India are +able to hunt later in the day than usual by using +spectacles glazed with golden yellow glass.</p> + + +<h3>THE FACTS OF COLOUR-BLINDNESS</h3> + +<p>When we consider the path along which a +visual impulse has to pass, and that each cell +has probably some special function in connection +with that impulse, it is not surprising that we +meet with a large number of different defects of +colour-perception and light-perception. Defects<span class="pagenum" id="Page_35">35</span> +of light-perception are quite distinct from defects +of colour-perception.</p> + +<p>1. <i>Defects of light-perception.</i>—The person +having the defect is placed in a similar position +to a normal-sighted person with those particular +rays removed or reduced to the same intensity. +Defects of light-perception may be caused by +absorption or by some defect in the visual purple +or cerebro-retinal apparatus. The chief defect of +light-perception which is found is shortening of +the red or the violet end of the spectrum. Let +us consider the influence of a shortened spectrum +upon colour-vision. The first evident fact is that +bodies reflecting only light, the rays of which +occupy the missing portion of the spectrum, +appear black.</p> + +<p>Nearly all colours are compound; that is to +say, the coloured body reflects other rays than +those of the colour seen. Thus a blue-green glass +may transmit the green, blue, and violet rays of +the spectrum. Let us suppose that we have a +substance reflecting the green, blue, and three-quarters +of the violet, the colour of the body to +a normal person being green. Then if we had +another substance which reflected the whole of +the violet, it would appear blue. But with a +person who could not perceive the terminal fourth +of the violet the colour would look exactly the +same as the green one, and as he could not distinguish +between the two he would be in continual +difficulty with blues and greens. All +coloured objects reflecting rays occupying the +missing portion appear darker than they do to<span class="pagenum" id="Page_36">36</span> +the normal-sighted, and are always matched with +darker colours belonging to a point more internal. +Thus a dichromic with a shortened red +end of the spectrum matches a red with a darker +green.</p> + +<p>It will be noticed that a shortened spectrum, +especially if one end only be affected, may interfere +very little with the general appreciation of +shade. If, for instance, we take a case in which +the red end of the spectrum is shortened, so that +only three-quarters of the red of the normal-sighted +is seen, then all bodies which equally reflect +or transmit these rays can be correctly compared, +because a similar portion of light has been +removed from each. It is only when one colour +reflects or transmits the rays occupying the +shortened portion, and the other does not, that +there is any definite interference with the appreciation +of shade. Again, if neither colour reflects +or transmits rays occupying the shortened portion +of the spectrum, there will obviously be no interference +with the appreciation of shade.</p> + +<p>A very common mistake due to shortening of +the red end of the spectrum is the confusion of +pink and blue. If a person with considerable +shortening of the red end of the spectrum is +shown a pink which is made up of a mixture of +red and violet, the red consisting of rays occupying +the missing portion of the spectrum, only +the violet is visible to him, and so the pink appears +a violet without a trace of red. This pink is therefore +matched with a violet or blue very much +darker than itself.</p> + +<p><span class="pagenum" id="Page_37">37</span></p> + +<p>Mistakes which are due to shortening of the +spectrum may be remedied if we subtract the +rays occupying the missing portion from the +colour of confusion. For instance, if we take a +blue and a pink which have been put together as +identical by a person with a shortened red end +of the spectrum, and look at them through a glass +which is opaque to the red, but transparent to +the remaining rays of the spectrum, both will +appear alike in hue and shade. A person with +considerable shortening of the red end of the +spectrum will look at a red light (which is so +dazzlingly bright to a normal-sighted person as +to make his eyes ache after looking at it closely +for a few seconds), at a distance of a few inches, +and remark that there is nothing visible, and that +the whole is absolutely black. It is obvious that +the light must consist only of rays occupying the +missing portion of the spectrum. The same remarks +which I have made for a shortened spectrum +apply to cases in which there is defect of +light-perception through absorption or any other +cause. The person having the defect is placed in +a similar position to a normal-sighted person +with those particular rays removed or reduced to +the same intensity.</p> + +<p>Another effect of shortening of the spectrum +when it is sufficient to interfere with the difference-perception +which appears to be inherent in the +central nervous system, is that the colours appear +to be moved in the direction of the unshortened +portion. For instance, we find the neutral point +of the dichromic, with shortening of the red end<span class="pagenum" id="Page_38">38</span> +of the spectrum, in most cases further towards the +violet end of the spectrum in comparison with a +case in which the spectrum is of normal length. +In the same way a trichromic with a shortened +red end of the spectrum has the junction of the +red and green nearer the violet end than in a case +where there is no shortening.</p> + +<p>The point that I specially wish to emphasise is +that, though every case in which there is defective +light-perception can be explained by a defective +sensibility to light of certain wave-length, +not a single case of the very large number of +persons that I have examined can be explained on +the older theories; that is, the defect of light-perception +cannot be explained on the assumption that +there is a defect in a light-perceiving substance +which is sensitive to rays of light from a considerable +range of the spectrum. A large number of cases +in which there is shortening of the red end +of the spectrum escape detection when only the +green test is used, as is usual according to Holmgren’s +instructions.</p> + +<p>2. <i>Defects of colour-perception.</i>—The colour-blind +have a diminished hue-perception and see +a less number of colours than the normal. All +the symptoms of colour-blindness are such as we +should expect from want of development of the +retino-cerebral apparatus for the perception for +colour. This is evident even in the slighter cases +which show a diminished colour-perception compared +with the normal. We find that the colour-blind +are much more dependent on the luminosity +of the colour than the normal-sighted; they require<span class="pagenum" id="Page_39">39</span> +a stronger stimulus; they fatigue more +easily with colours than the normal-sighted; they +have a more marked simultaneous contrast; the +visual angle subtended by the coloured object +requires to be larger, and they have a very bad +memory for colours. The diminution of colour-perception +with a diminished visual angle evidently +depends upon several causes. It is very +marked when there is diminished light-perception +for those rays which are imperfectly seen. It is +also dependent upon certain retinal conditions, +as in scotoma and allied conditions. There are +colour-blind persons, however, who are able to +recognise colours under as small a visual angle +as the normal-sighted, and I have examined +one dichromic (said to be red-blind by a physicist) +who recognised red easily through the thickest +neutral glass of my lantern, and who had no +difficulty with this colour at a distance.</p> + +<p>Apart from any other defect of light or colour-perception, +every case with which I have met has +fallen naturally into one of the classes I have +given; that is to say, every person is either +heptachromic, hexachromic, pentachromic, tetrachromic, +trichromic, dichromic, or totally colour-blind. +When I first gave this classification of +colour-blindness, the facts that I discovered were +so at variance with those generally stated that it +was very difficult for those who were not well acquainted +with the subject to compare the two +sets. The general knowledge of the subject has, +however, steadily increased, and the facts which +I had so great a difficulty in getting recognised<span class="pagenum" id="Page_40">40</span> +now form part of our common knowledge. It +would be well, therefore, to describe the two main +varieties of colour-blindness which are of chief +practical importance, and to show the relation +which they bear to the writings of other persons. +These two main varieties have dichromic and +trichromic vision.</p> + +<p>1. <i>Dichromic vision.</i>—The cases which come +under this head form the class of the ordinary +red-green blind. It is under this head that nearly +every one of the recorded cases may be classed. +Vision, as far as colour is concerned, is dichromic, +the neutral point being situated in the green of +the normal-sighted at about λ 500. All the +colours on the red side tend to be confused with +each other; therefore red, orange, yellow and +half of the green are seen as one colour, the remainder +of the green, blue and violet as the +other. The luminosity curve in uncomplicated +cases is similar to the normal. There may be +shortening of the spectrum at either the red or +the violet end of a varying degree. All degrees +of shortening of the red end of the spectrum may +be found. Dichromics with normal luminosity +curves are those which were formerly designated +green-blind; but this designation is not in accordance +with the facts, because there is no +defect of light-perception in the green, and the +so-called diagnostic mistakes, as, for instance, +putting a bright green with a dark red, are not +made. Cases of so-called red-blind are dichromics +with shortening of the red end of the spectrum. +I have shown that the defective perception of<span class="pagenum" id="Page_41">41</span> +the red end of the spectrum will not account for +the dichromic vision which is found in these +cases. We may also meet with shortening of the +spectrum with otherwise normal colour-perception. +We also meet with dichromic cases forming +a series from almost total colour-blindness to +those bordering on the trichromic. Any theory +must account for the fact that there are varying +degrees of colour-blindness in dichromic vision, +and why there is a large neutral band corresponding +to the colours of the centre of the spectrum +in some cases, and in others the neutral band is +so small that the dichromic cannot mark it out. +The two colours seen by the dichromic are red and +violet, though where no distinction is seen between +yellow and red, and blue and violet, the brighter +colour will often be selected; that is why so many +dichromics say that they see yellow and blue in +the spectrum. Those who have had practical +experience of colour-blindness will know, however, +that many dichromics make no mistakes +with the red test. The following will give the +normal-sighted the best idea of colour-blindness, +and it is how the dichromic see the spectrum, +and explains why they are able to distinguish +between colours. Let him regard the dichromic +as a man who has two colours—red and violet +and white. The purest red is at the red end of +the spectrum; this becomes less and less saturated +as the violet is approached until the neutral +or white point is reached; then violet comes +into the white, and this increases in saturation +to the termination of the violet. The ordinary<span class="pagenum" id="Page_42">42</span> +dichromic therefore sees green as a much whiter +and less saturated colour than red.</p> + +<p>2. <i>Trichromic vision.</i>—These persons see three +distinct colours in the spectrum—red, green and +violet. They describe the region intermediate +between red and green; that is to say, the orange +and the yellow as red-green, and blue as violet-green. +It will be seen, therefore, that their chief +difficulty is distinguishing yellows and blues. A +yellow, for instance, which is situated next to a +green will be called red, and the same yellow +when adjacent to a red will be called green. +There are various degrees of trichromic vision, +varying from those who are little better than +dichromic to those who are tetrachromic. The +trichromic rarely find any difficulty with their +three main colours—red, green and violet.</p> + +<p>These cases have been described under the +name of anomalous trichromatics. This name is +one which has been given to those persons who +in making a match between a yellow corresponding +to the sodium flame and a mixture of thallium-green +and lithium-red make a mixture which is +different to that of the normal.<a id="FNanchor_9" href="#Footnote_9" class="fnanchor">9</a> A man who +puts too much green in the mixture is called a +green anomaly; whilst a man who puts too much +red in the mixture is called a red anomaly. The +red anomaly is only a trichromic with shortening +of the red end of the spectrum, and this may be +as extensive as in any case of dichromic vision. +I have, however, described trichromic cases which<span class="pagenum" id="Page_43">43</span> +had all the symptoms attributed to the anomalous +trichromatics, but they were not anomalous +trichromatics, as they made an absolutely normal +match.<a id="FNanchor_10" href="#Footnote_10" class="fnanchor">10</a></p> + + +<hr class="chap x-ebookmaker-drop"> + +<div class="chapter"> +<p><span class="pagenum" id="Page_44">44</span></p> +<h2 class="nobreak tac fs130" id="LECTURE_II">LECTURE II</h2> +</div> + +<p class="tac ptb05"><i>Delivered on February 3rd</i></p> + +<h2><span class="smcap">The Detection of Colour-Blindness from +a Practical Point of View</span></h2> + + +<p>I. <i>Object of a test for colour-blindness.</i>—Tests +for colour-blindness are of two kinds; namely, +those which are used for the purpose of ascertaining +the special phenomena of colour-blindness, +and those which are employed when the inquiry +is made for some practical purpose. As with +visual acuity, it is necessary to fix an arbitrary +standard. As we do not wish to exclude a greater +number than is absolutely necessary, the object of +the test should be to exclude dangerous persons +and dangerous persons only. These persons may +have other duties to perform which do not require +them to possess a perfect colour-sense. I should, +however, like to see those persons who are specially +qualified for a certain position, occupy it, for +instance, men who have to keep a look-out on our +most important ships being selected because of +their accurate colour-vision and visual acuity. +I do not mean that I would select only those men +and reject the others, but that I should like to see +a second object of a test, namely, to select those +who are specially efficient so that the Captain +might know on whom to rely in conditions of +exceptional difficulty.</p> + +<p><span class="pagenum" id="Page_45">45</span></p> + + +<p>II. <i>The requirements of a test for colour-blindness.</i>—A +test for colour-blindness, when it is to be +employed for some definite and specific purpose, +as, for instance, excluding dangerous persons from +certain callings, should be such as to show +definitely that the persons rejected are dangerous. +It is very useful to demonstrate to the men and +their fellows that a rejected candidate is dangerous. +The colleagues of a rejected candidate would +refuse to risk their lives with a man who before +their eyes called a red light, green. I was expressing +these views when a superintendent of a +railway company, who is using my lamp, told me +that he had adopted this method with great +satisfaction to himself and to the men. A man, +for instance, who has been working twenty years +on the railway has been rejected for colour-blindness. +He has complained bitterly to the superintendent, +at the same time declaring emphatically +that he is normal-sighted. The superintendent +has replied, “You know red?”—“Yes.” “You +know green?”—“Yes.” “You will therefore +agree that if you call green, red; or red, green, +you ought to be rejected. Bring two or three of +the other men in with you and I will test you.” +The man has readily agreed to this. The superintendent +has then tested him by asking him to +name various coloured objects in the room, and +knowing by experience exactly the coloured +objects which are miscalled by the colour-blind +readily exposes his defect. It is noteworthy that +on some occasions a colour-blind man has been +tested by another person in the same room without<span class="pagenum" id="Page_46">46</span> +making any of the mistakes which he subsequently +made, because none but coloured objects +which he could readily recognise were shown to +him. This is an example of the necessity of a +practical knowledge of colour-blindness in an +examiner. On account of the arrangement of +signals by sea and land, it is necessary that +persons employed in the marine and railway +services should be able to recognise and distinguish +between the standard red, green, and +white lights in all conditions in which they are +likely to be placed. An engine-driver or sailor +has to name a coloured light when he sees it, not +to match it. He has to say to himself, “This is +a red light, therefore there is danger”; and this +is practically the same as if he made the observation +out loud. Therefore, from the very commencement +we have colour-names introduced, +and it is impossible to exclude them. The engine-driver +is told that red is a “danger” signal, +green a “caution” signal, and white an “all +right” signal. Therefore, it is absolutely +necessary that he should know the meaning of +these colour-names. A test should be such as to +make it impossible for the examinee to be coached +through it. This is one of the most important +requirements of a test for colour-blindness and +one that is rarely fulfilled. Nearly every one of +the tests in general use fail on this account.</p> + +<p>A test should be one which can be carried out +as rapidly as is possible with absolute efficiency; +of two equally efficient tests the one which takes +the least time must be selected. A test, therefore,<span class="pagenum" id="Page_47">47</span> +should have no unnecessary details which though +of theoretical interest are not concerned with the +object in hand. The test should be made as easy +and as little complicated for the examiner as +possible.</p> + + +<p>III. <i>Persons to be excluded.</i>—We wish to exclude +all those individuals who are included in the +following three classes: (1) Those who see three +or less colours in the spectrum. (2) Those who, +whilst being able to perceive a greater number of +colours than three, have the red end of the +spectrum shortened to a degree incompatible with +their recognition of a red light at a distance of two +miles. (3) Those who are unable to distinguish +between the red, green, and white lights at the +normal distance through defect or insensitiveness +of the cerebro-retinal apparatus when the image +on the retina is diminished in size.</p> + +<p>I will now explain why these three classes of +persons should be excluded. The first class +includes the trichromic, the dichromic, and the +totally colour-blind, in accordance with the +facts previously stated. The trichromic never, +in ordinary circumstances, mistake green for red, +but confuse yellow with green or red. Colour is a +feeble quality of objects to them, and nervousness +or excitement may reduce them to the condition +of the dichromic. The dichromic are liable to +mistake a green light for red, and vice versa. It +is very important that persons belonging to the +second class should be excluded, and yet none of +the ordinarily used tests detect them. The rays<span class="pagenum" id="Page_48">48</span> +of red at the extreme left of the spectrum are the +most penetrating, as may be seen by looking at a +light or the sun on a foggy day, or through +several thicknesses of neutral glass. It is chiefly +by these rays that we recognise a red light at a +distance; and it is therefore of great importance +that a sailor or engine-driver should be able to +perceive them. The third class contains persons +who are able to distinguish colours easily when +they are close to, but fail to distinguish them at a +distance, owing to the nerve-fibres supplying the +central portion of the retina being impaired. As +a light at a distance occupies the central portion +of the visual field, it is essential that the corresponding +portion of the retina should be normal. +There are cases of central scotoma for colours with +perfect form-vision; these would, therefore, not be +detected by a test for visual acuity. This class +also includes those who without having a scotoma +are unable to distinguish between colours at the +normal distance when the image on the retina is +diminished in size.</p> + + +<p>IV. <i>The construction of a test for colour-blindness.</i>—In +the construction of a test for colour-blindness, +the facts of colour-blindness must be utilised so +that the object and requirements of the test are +fulfilled. The following facts are of practical +importance.</p> + +<p>1. <i>Most colour-blind make mistakes with certain +colours, but are correct with regard to others.</i> This +may be illustrated in the following way. Let us +take an ordinary dichromic, and, having given<span class="pagenum" id="Page_49">49</span> +him the set of wools belonging to the Classification +Test, ask him to pick out all the reds. On examining +the pile of wools selected as reds, it will be +found that the majority are red, but in addition +there will be some browns and yellow-greens. +If he be then told to pick out the whole of the +greens the greater number of those selected will be +green, but there will be also greys, browns, and +reds. In each case, it will be seen that the +majority of wools are of the desired colour.</p> + +<p>If another dichromic be examined in the same +way it will be found that, though he may not make +exactly the same mistakes, he will in all probability +pick out the same greens to put with the +reds, and the same reds to put with the greens. +The same result will be obtained if the colour-blind +persons be asked to name a large number of +colours. They will in most cases name the colour +correctly. It will be noticed that the greens which +were put with the reds when classifying the +colours, will be called red in naming them. It is +evident that the same idea has guided the colour-blind +in each case. This shows that, though a +person may be red-green blind, he is not absolutely +red-green blind in the sense of being totally +unable to distinguish between the two colours. +The fact that they are actually judging by colour +may be demonstrated by giving them coloured +materials of different kinds, or by asking them to +name a large number of coloured objects.</p> + +<p>It will be seen that if we take a dichromic and +ask him to name a number of red and green wools, +in the majority of instances he will name them<span class="pagenum" id="Page_50">50</span> +correctly. But as, almost invariably, the same +wools are chosen, for all practical purposes the +same result would be obtained by asking a person +to name a few of these wools. What more decided +and brighter greens could we have than Nos. 76 +and 94 of my Pocket Test? yet these are two of +the greens which are called reds by the dichromic. +We should have accomplished as much by asking +a colour-blind person to name Nos. 76 and 94 as if +we had asked him to name a large number of +greens. The colours in a test should, therefore, be +those which the colour-blind are particularly +liable to miscall. At the same time, their nature +should be unmistakable to the normal-sighted.</p> + +<p>2. <i>The colour-blind name colours in accordance +with their colour-perception, and thus show definitely +to which class they belong.</i> I have not come +across a man who has guessed correctly when +examined with my test. A man who did guess +would know that he was incompetent. As the +colour-blind are often not aware of their defect +they answer as they see, only guessing when they +feel uncertain as to the nature of the colour shown. +There is probably more misapprehension on this +point than on any other in the practical testing of +colour-blindness.</p> + +<p>3. <i>Colours may be changed to the colour-blind, +whilst leaving them unaltered to the normal-sighted.</i></p> + +<p>4. <i>The phenomena of simultaneous and successive +contrast are much more marked for the colour-blind +than for the normal-sighted.</i> Two colours, which +have not changed in the slightest degree to the +normal-sighted on being contrasted, have apparently<span class="pagenum" id="Page_51">51</span> +altered very considerably to the colour-blind. +As an example of this, let us take a pure deep +yellow, a bright red, and a bright green. To the +normal-sighted the yellow will be altered very +little by comparison with the red or the green, but +a trichromic would say that the colour was green +when contrasted with the red, red when contrasted +with the green. This principle of exaggerated +contrast must be borne in mind when examining a +candidate. Thus if a trichromic be doubtful about +a yellow, but seems inclined to call it green, he +should be given a pure green to compare with it. +In the same way, in showing the coloured lights, +the same colour produced in a different way +should often be shown. Thus an orange-red may +be shown immediately after a pure red. This will +not alter the colour to the normal-sighted, but +greatly facilitate the examination of the colour-blind.</p> + +<p>5. <i>Many colour-blind match correctly, but name +the principal colours wrongly.</i> Therefore the test +must be a naming test, the examinee being +rejected if he confuse the colours which it is +essential he should distinguish between in his +occupation.</p> + +<p>6. <i>Many colour-blind recognise colours easily +when they are close to them, or the surface is large, +but fail to distinguish between them when they are at +a distance or the image on the retina is small.</i> The +test must be constructed in conformity with these +facts.</p> + +<p>7. <i>The colour-blind are more dependent upon +luminosity than the normal-sighted, and are liable to<span class="pagenum" id="Page_52">52</span> +mistake a change in luminosity for a change of +colour.</i> The test should have a means of rapidly +changing the luminosity of a colour.</p> + +<p>8. <i>The colour-blind find special difficulty with +faint and dim colours.</i> The test should have +colours of this kind.</p> + +<p>9. <i>The colour-blind who have shortening of the +red end of the spectrum cannot see reds reflecting or +transmitting only rays corresponding to the shortened +portion.</i> It is essential that reds of this kind +should form part of the test.</p> + +<p>10. <i>The colour-blind find more difficulty in +comparing colours when different materials are used, +than when the coloured objects are all of the same +nature.</i></p> + +<p>11. <i>Most colour-blind find more difficulty with +transmitted than with reflected light.</i></p> + +<p>12. <i>The colour-blind have a defective memory for +colours.</i></p> + +<p>13. <i>Colours may be changed to the normal-sighted +whilst leaving them unchanged to the colour-blind.</i> +When three colours of the normal-sighted are +included in one of the colour-blind, it is obvious +that a change from one colour to another of the +three will make no difference to the colour-blind. +Also when the spectrum is shortened, the addition +or rays corresponding to the shortened portion to +another colour will not alter its appearance to the +person with the shortened spectrum. For instance, +to a person with shortening of the red end of the +spectrum, a blue will still remain blue, when so +many red rays from the shortened portion have +been added to it as to make it appear rose to the +normal-sighted.</p> + +<p><span class="pagenum" id="Page_53">53</span></p> + +<p>14. <i>The colour-blind may have a sense of luminosity +similar to that of the normal-sighted.</i></p> + +<p>15. <i>The dichromic distinguish between the colours +of the normal-sighted, which are included in +one of theirs by their relative luminosity and the +difference of saturation which is apparent to them.</i> +A test should therefore have the means of presenting +colours of different saturation in succession.</p> + +<p>16. <i>Colour-blindness is frequently associated with +very high intelligence and exceptional ability.</i></p> + + +<p>V. <i>The Lantern Test.</i><a id="FNanchor_11" href="#Footnote_11" class="fnanchor">11</a>—1. <i>Description of apparatus.</i> +The lantern contains four discs: three carrying +seven coloured glasses, and one with seven modifying +glasses. Each disc has a clear aperture. The +other mechanical details are: an electric or oil +lamp with projecting accessories, a diaphragm for +diminishing the size of the light projected, handles +for moving the discs and the indicator showing the +colour or modifier in use. The diaphragm is +graduated in respect to three apertures to represent +a <span class="nowrap">5 <span class="fraction"><span class="fnum">1</span><span class="bar">/</span><span class="fden">2</span></span></span>‑inch railway signal bullseye at 600, 800, +and 1000 yards respectively when the test is made +at 20 ft. The glasses are as follows:—-</p> + +<div class="center"> +<table> +<tr> +<td class="tac" colspan="2"><div> <i>Coloured glasses.</i>  </div></td> +<td class="tac pl2" colspan="3"><div><i>Modifying glasses.</i></div></td> +</tr> +<tr> +<td class="tar pr05"><div>1.</div></td> +<td class="tal">Red (A and B).</td> +<td class="tar pl2 pr05"><div> 7.</div></td> +<td class="tal" colspan="2">Ground glass.</td> +</tr> +<tr> +<td class="tar pr05"><div>2.</div></td> +<td class="tal">Yellow.</td> +<td class="tar pl2 pr05"><div> 8.</div></td> +<td class="tal" colspan="2">Ribbed glass.</td> +</tr> +<tr> +<td class="tar pr05"><div>3.</div></td> +<td class="tal">Green.</td> +<td class="tar pl2 pr05"><div> 9.</div></td> +<td class="tal">Neutral </td> +<td class="tal">(No. I).</td> +</tr> +<tr> +<td class="tar pr05"><div>4.</div></td> +<td class="tal">Signal Green.</td> +<td class="tar pl2 pr05"><div>10.</div></td> +<td class="tal">  "</td> +<td class="tal">( "  II).</td> +</tr> +<tr> +<td class="tar pr05"><div>5.</div></td> +<td class="tal">Blue.</td> +<td class="tar pl2 pr05"><div>11.</div></td> +<td class="tal">  "</td> +<td class="tal">( " III).</td> +</tr> +<tr> +<td class="tar pr05"><div>6.</div></td> +<td class="tal">Purple.</td> +<td class="tar pl2 pr05"><div>12.</div></td> +<td class="tal">  "</td> +<td class="tal">( " IV).</td> +</tr> +<tr> +<td class="tar"></td> +<td class="tal"></td> +<td class="tar pl2 pr05"><div>13.</div></td> +<td class="tal">  "</td> +<td class="tal">( "  V).</td> +</tr> +</table> +</div> + +<p><span class="pagenum" id="Page_54">54</span></p> + +<figure class="figcenter illowe25_625" id="i_54"> + <img class="w100" src="images/i_54.jpg" alt=""> + <figcaption><p>Fig. 3.</p></figcaption> +</figure> + +<p>It will be noticed that three of the discs are +similar in every respect. In some of my lanterns +the two reds are put at the end of the series of +colours and numbered Red 1 and Red 2. This +makes no important difference, but the arrangement +given here is more convenient. It should be +noted that Red 1 corresponds to Red B and +Red 2 to Red A. If the electric lamp should +get broken the projecting apparatus can be<span class="pagenum" id="Page_55">55</span> +removed and an ordinary kerosene lamp placed +behind the aperture.</p> + +<figure class="figcenter illowe23" id="i_55"> + <img class="w100" src="images/i_55.jpg" alt=""> + <figcaption><p>Fig. 4.</p></figcaption> +</figure> + +<p>2. <i>Reasons for special construction.</i>—The lantern +has been constructed conformably with the requirements<span class="pagenum" id="Page_56">56</span> +and facts of colour-blindness. All the +facts I have given have been considered in +constructing the lantern.</p> + +<p>The examiner, on possessing a lantern for the +first time, should carefully test himself with it and +ascertain how the different lights appear to him +with different conditions of general illumination. +It is probable that certain improvements may +suggest themselves to him, therefore, I think it +will be advisable to deal with certain of these +points, as it will help the examiner in the use of the +lantern. The colours have never been altered, and +I certainly should have altered them if I could +have improved the lantern by doing so. I have +never met a single colour-blind person who has +not been readily and easily detected with my +lantern, though I have examined many who have +passed other lanterns and in some cases a number +of other tests for colour-blindness. In most cases +one turn of the wheel will be sufficient to make a +colour-blind person disclose his defect.</p> + +<p>The examiner may be dissatisfied with the +colour of the blue; let us, therefore, compare an +examination of a normal-sighted person with that +of an ordinary dichromic. The normal-sighted +person will name every one of the colours with ease +and certainty, with perhaps the exception of the +blue, with which he is in some doubt. Here is the +result of an examination of an ordinary dichromic: +he called the yellow, green; the green, red; the +signal green, no colour; the blue, blue; the +purple, green; red A, no colour or light; red B, +green. It will be noticed that the only colour<span class="pagenum" id="Page_57">57</span> +that he has correctly named is the blue. We can +try him again and again, and though he will mistake +all the other colours he will always name +the blue correctly. The examiner will have learnt +from this several important facts. He will see +that the colour-blind are really guided by their +sensations of colour, and that it is not simply a +matter of guessing. The more an examiner has +practical experience of colour-blindness, the more +will he recognise the fact that the colour-blind +are guided by their sensations of colour. He will +notice that the dichromic has readily recognised +the blue which was scarcely apparent to him (the +examiner), and therefore cannot have overlooked +as a matter of carelessness colours which are much +more apparent to the normal-sighted. The blue is +a valuable colour for other reasons, for though it is +not a colour on which I reject candidates, anyone +miscalling it must be very carefully examined +before he is passed. The trichromic generally +call this blue, green. If we wish to obtain a +purer blue, we can do so by combining the blue +or the purple with the signal green.</p> + +<p>Again, the examiner may think that it might +be better to have an apparatus which showed +two or three lights instead of only one. I will +therefore give my reasons for adopting only one. +This point was one which occupied my attention +for a considerable time, especially in view of the +fact—which, as far as I am aware, I was the first +to discover—that simultaneous contrast is increased +to the colour-blind. I was naturally +anxious to turn this fact to account. I found,<span class="pagenum" id="Page_58">58</span> +however, that I gained nothing by increasing the +number of lights, and that in many cases it was +a source of error. A second or third light could +have been easily added to my lantern, but besides +unnecessarily complicating the apparatus +it would have served no useful purpose. All the +results which are obtained with simultaneous +contrast are obtained even more effectively with +successive contrast. It will be noticed that when +lights are seen in ordinary conditions they are +conditions of successive contrast, and not of +simultaneous contrast. An observer rarely keeps +his eyes definitely fixed on one light whilst he +names those adjacent to it, but moves his eyes +so that the images of the respective lights fall +successively on his foveas. When more than one +light is employed, all the disadvantages of matching +as against naming are introduced. It will be +seen that by presenting one light after another +we are fulfilling all the necessary conditions, only +that the light is moved instead of the eyes, sufficient +time being allowed to elapse to enable a +normal-sighted person to readily recognise the +true colour of the next light without being confused +by the after-image of the one he has just +seen. Many nervous normal-sighted would name +a yellow light seen between two red lights as +green, and it does look green to them from ordinary +physiological conditions. They look first at +one red light, then immediately at the yellow +light, then at the second red light, and then again +at the yellow light until they feel sure that the +centre light is a green light, and say so. I have<span class="pagenum" id="Page_59">59</span> +never met with a normal-sighted person who has +miscalled the unmodified light of my lantern, either +red or green. Many humble, nervous normal-sighted +persons are under the impression that they are +colour-blind, and yet would make perfectly efficient +officers. Many of these men have been told +by their wives or other persons that they are +colour-blind, and, believing this, try to see colours +which are not visible to them. I have examined +many persons of this description, and have noted +the ease and accuracy with which they have gone +through the tests for colour-blindness when they +have been assured by me that they were normal-sighted. +On the other hand, it is often very +difficult to convince a self-reliant, colour-blind +person that he is colour-blind. He is on the look-out +for the small differences which he notices +between colours, and the fact of having another +light for comparison gives him the desired clue, +and, though colour-blind, he passes the test.</p> + +<p>The material is the best possible, as it will not +fade like all dyed substances, and therefore all +records made with one set of apparatus will be +uniform. Again, a coloured light has none of the +accessory qualities which enable the colour-blind +to pass through other tests. Thus many dichromics +will call the yellow glass red or green, +who would not think of putting a yellow with a +green or red wool, on account of the difference in +luminosity. He will, in the same way, if told to +pick out colours in the Classification Test to +match the colour of the light shown, have to +depend upon his colour-perception. This is a<span class="pagenum" id="Page_60">60</span> +useful method with nervous and undecided candidates. +The objection to it is that it cannot be +carried out in the dark or in a dark room. The +Test is not open to any of the objections which +may be urged against the method of simply +naming colours, because the character and intensity +of the colour may be changed at will.</p> + +<p>The method is better than that of direct comparison, +because the candidate is forced to use +his colour-perception, and has to compare the +colour seen with previous impressions of colour +in his mind. By the use of neutral glasses, etc., +I have obviated the fallacy of the method of +naming colours (namely, that these can be distinguished +by their saturation and luminosity), +and forced the individual to depend upon his +colour-perception, and not upon some other accessory +quality of the object seen.</p> + +<p>No amount of coaching will enable a colour-blind +person to pass this test, whilst almost any +other may be passed in this way. I have tried +on many occasions to coach a man so as to pass +my lantern, and without success. The combinations +are so numerous that the only result is +to make the colour-blind man nervous and doubtful +and more easily detected than before. This +has occurred with men who could pass other tests +with ease.</p> + +<p>The test also has a quality possessed by no +other—namely, that of enabling the examiner to +reject dangerous persons and dangerous persons +only, the lower degrees of colour-blindness being +allowed to pass.</p> + +<p><span class="pagenum" id="Page_61">61</span></p> + +<p>3. <i>Special directions for conducting the test.</i>—(1) +The candidate should be seated at a distance +of twenty feet from the lantern. (2) He should +be asked to name the colour of the light produced +by a coloured glass (1 to 6) alone, or in combination +with another coloured glass or glasses, +or with the modifying glasses (7 to 13). (3) A +candidate should be rejected (i) if he call the red, +green, or the green, red, in any circumstances; +(ii) if he call the white light, in any circumstances, +red or green, or vice versa; (iii) if he call the red, +green, or white lights, black, in any circumstances. +(4) A candidate who makes mistakes, +other than those mentioned above, should be put +through a very searching examination. It is not +necessary to have the room absolutely dark; in +fact, I prefer a certain amount of light. The +examiner can, if he wish, make the test at night +in the open air.</p> + +<p>The examiner should on no account conduct +the examination on any regular plan, because the +candidate, anxious to pass, finds out from persons +who have already passed the order and method +of the examination, and so, though colour-blind, +might obtain a certificate. Any one of the glasses +may be shown first, and the candidate required +to name the colour of the light. The following +will serve as an example of the method to be employed +in testing a candidate. A red being +shown, the candidate is required to name its +colour. Then a blue or green may be substituted. +It is best to use the largest aperture at first and +to show all the colours on one disc. This will<span class="pagenum" id="Page_62">62</span> +give confidence to the normal-sighted candidate, +whilst most of the colour-blind will be detected. +In the case of candidates who appear to be normal-sighted +and yet very nervous, there is no harm +in telling them after they have named all the +colours on the disc correctly that this is the case. +No comment should, however, be made on individual +answers. Then one of the neutral, +ground, or ribbed glasses should be inserted, not +the slightest intimation being given to the candidate +of the nature of the colour. He should be +asked to name or describe the light, and the +answer, if incorrect, together with his other replies, +carefully recorded. The other glasses may +then be shown, a combination of the neutral, +ground, ribbed, and coloured glasses being used +at irregular intervals.</p> + +<p>When the candidate has been examined with +the largest aperture, the examiner can go through +the same procedure with one of the smaller apertures. +I have found the third aperture the one +which is most generally useful. On account of +the great diminution of total luminosity caused +by the diminished area of the light source, the +three smallest apertures can only be used in a +dark room.</p> + +<p>If a candidate hesitate about a colour and +ultimately name it correctly, a second and, if +necessary, a third glass of the same colour should +be combined with the first. The fact that in one +case a single glass is used, and in another two or +three of the same coloured glass, makes very little +difference in the colour of the light to the normal-sighted.<span class="pagenum" id="Page_63">63</span> +This is not the case with the colour-blind; +a dichromic who has hesitated about a +green and then correctly named it may emphatically +call the light red when another green glass +is put in front of the first.</p> + +<p>Care must be taken when the candidate is going +to be examined with two glasses at once, such as +one of the neutral, ground, or ribbed glasses, and +a coloured glass, that he does not see the light +until both are in position, or else he may see the +colour before it is modified in the necessary way.</p> + +<p>If the candidate call the standard red, green; +or the standard green, red, in any circumstances—that +is, either alone or in combination with the +modifying glasses—he is to be rejected.</p> + +<p>The examiner should ascertain for himself how +far the various colours are visible when modified +with the neutral glasses. If the red and green +be not visible with the thickest neutral in the +conditions of luminosity and external lighting +which the examiner is employing, he should use +the darkest neutral which allows the colours to +be plainly visible to the normal-sighted. In all +cases of doubt the examinee should be asked to +walk towards the lantern and told to say when +the light is visible, and asked to name its colour. +The distance at which the light is visible, and +then that at which the colour is visible, should +be noted and compared with the normal.</p> + +<p>Particular attention should be paid to the +answers given to the combination of the thickest +neutral glass with the standard red and green +respectively.</p> + +<p><span class="pagenum" id="Page_64">64</span></p> + +<p>The examiner should utilise the fact that successive +contrast is increased in the colour-blind, +as this is an easy method of detecting the trichromics. +The red having been shown, the light +should be quickly changed to yellow or clear, +the examiner’s hand being placed over the aperture +if there be any intervening colours. It is +necessary that the yellow should be shown immediately +after the red without any intervening +colours being first seen by the candidate. The +normal-sighted do not see any change in the +yellow or clear when they are shown after the red +light, but the trichromic call the yellow light, +green. The examinee should then be shown the +green light, and then the yellow or clear, in the +same way as mentioned for the red. The normal-sighted +will easily recognise the yellow, but the +trichromic will call it red. This portion of the +examination must never be omitted in any examination +in which the candidate is passed. The +two divisions of the test—that is, showing yellow +immediately after red and after green—may be +used at different periods of the examination, and, +if there be any doubt, repeated.</p> + +<p>An examiner should, as far as possible, with +the exceptions given in the instructions, avoid all +conversation with the candidate, simply asking, +“What colour is this?” and recording the answer +without comment. If an examiner after each +answer say, “Quite right,” or some such expression, +the following is likely to occur. The +candidate after, say, six correct answers, makes a +mistake; the examiner says, “Are you sure?”<span class="pagenum" id="Page_65">65</span> +Then the candidate knows at once that he has +made a mistake, and makes a guess, very probably +a correct one. When a similar colour is +shown subsequently, he remembers the mistake +he made, and gives the second, and probably the +correct answer.</p> + +<p>In addition to being an efficient test, it is a very +rapid test, as many men who have been certified +as normal after a lengthy examination with other +tests have at once disclosed their defect by calling +the green light of the lantern red. Many are +under the impression that in an examination with +the lantern the dichromics simply guess. This +is entirely wrong. A man who did guess would +know that he was incompetent. I find that men +have named the coloured lights in strict accordance +with their colour-perception. A man may, +however, guess if examined by an inexperienced +and ignorant examiner, who when the examinee +has made a mistake promptly corrects it in a +cross tone. A normal-sighted person will guess +when examined in this way. The examiner must +receive the examinee with a smiling face and +courteous manner, and appear pleased and satisfied +with the answers, no matter what they may +be. The candidate is then placed at his ease, and +answers according to his colour-perception. It +will be noticed that the lantern detects those who +have a slightly diminished colour-perception, as +well as the dangerous varieties of colour-blindness. +The former undoubtedly are not as efficient +as those who have a normal colour-perception, so +that a definite standard will have to be fixed, as<span class="pagenum" id="Page_66">66</span> +in the case of visual acuity. Further details will +be found in my book on Colour-Blindness.<a id="FNanchor_12" href="#Footnote_12" class="fnanchor">12</a></p> + +<p><i>Summary of method of examination.</i>—(1) Show +all the colours on one disc with the largest aperture. +(2) Show the reds, greens, and yellow modified +by the neutral glasses. (3) Show all the +colours on one disc with Number 3 aperture. (4) +Show red, then immediately afterwards yellow +with largest aperture. Then show green and +yellow immediately afterwards. (5) Test the +candidate with the red, green, and yellow with +the smallest aperture. (6) Show the neutrals or +ground glass alone. (7) Show blue made by combining +blue or purple with the signal green. (8) +Show a colour, for instance, green, and then combine +another glass of the same colour. (9) Show +the red produced by the combination of purple +with red A. (10) Give the combination of red A +and signal green.</p> + + +<p>VI. <i>Other tests for colour-blindness.</i>—I have +three other tests for colour-blindness: the Classification +Test, the Pocket Test, and the Colour-perception +Spectrometer. I have also devised an +instrument for estimating the exact amount of +red, at different wave-lengths, which is necessary +to neutralise the complementary in different +persons.</p> + +<p>1. <i>The Classification Test.</i>—(<i>a</i>) <i>Description.</i>—This +test consists of 4 test colours and 180 confusion +colours; 150 coloured wools, 10 skeins of +silk, 10 small squares of coloured cardboard, and 10<span class="pagenum" id="Page_67">67</span> +small squares of coloured glass. The whole series +of colours is represented. In addition, there are +a large number of colours which have been chosen +by colour-blind persons as matching the test +colours. The test colours are Orange, Violet, Red, +and Blue-green, labelled I, II, III, and IV respectively. +The colours are chosen with the view +of presenting as much difficulty as possible to +the colour-blind, and as little as possible to the +normal-sighted. The colour-blind find especial +difficulty in matching or naming a colour lying +at the junction of two of their colours. As the +normal-sighted often find difficulty in saying +which colour predominates in a blue-green, so do +the tetrachromic with their purple-green, or the +trichromic with their red-green. A colour-blind +person may, however, match a colour correctly +which corresponds to the centre of one of his +colours. In addition to choosing those colours +for tests which are particularly liable to be mistaken +for other colours by the colour-blind, I have +used coloured materials of different kinds—wools, +silks, glass, and cards—so as to force the colour-blind +to judge by colour, and not by saturation +or luminosity. (See Fig. 5.)</p> + +<figure class="figcenter illowe28_125" id="i_68"> + <img class="w100" src="images/i_68.jpg" alt=""> + <figcaption><p>Fig. 5.</p></figcaption> +</figure> + +<p>(<i>b</i>) <i>Method of examination.</i>—The candidate +should be given the four test colours, and, having +named each, he should be told to select all those +which are similar in colour to the test colour. +He should be told to pay no attention to the fact +of a colour being lighter or darker; as long as it +is the same colour it should be put with the test +skein. The examiner should not go through the<span class="pagenum" id="Page_68">68</span> +test before the candidate first of all, neither +should one candidate be allowed to watch another +making his selection. A shrewd colour-blind +person might pass the test if he had seen a normal-sighted +person go through it previously. In order +to show the candidate the difference between a +shade and a colour, the examiner should take +one of the wools which is not a test colour—blue, +for instance—and pick out four or five shades of +the colour. The wools should be arranged without +the knowledge of the candidate, so that a +yellow or a grey is placed beside a red and the +examinee asked to name its colour. At another +period of the examination the yellow should be +placed adjacent to a green, and the examinee +again asked to name it.</p> + +<p><span class="pagenum" id="Page_69">69</span></p> + +<p>The examinee may pick out a certain number +of colours correctly, and then stop, saying that +there are no more exactly like the test colour. +This may embarrass the examiner; he should, +however, examine any candidate who has omitted +any colours as carefully as if mistakes had been +made. He should ask the candidate to match +one of the omitted colours.</p> + +<p>The examiner will soon find out from experience +those colours which are named and matched +wrongly by colour-blind persons; he should ask +the examinee to name some of these colours.</p> + +<p>Any candidate should be rejected who calls an +orange or red, green or brown; black, red or vice +versa; or green, either purple, rose, red, grey, +brown, or violet. Similar mistakes in matching +necessitate objection. A candidate who puts +purple, rose, or blue with violet, or yellow-brown +with orange is most probably dangerously colour-blind +and should be very carefully examined. +There are cases which pass the Holmgren test +with ease that fail in the most conclusive manner +with my Classification Test. They put green with +orange, brown and black with red, and grey with +blue-green. This is due to a different selection +both of test colours and confusion colours. Orange +is by far the most important test colour, and its +confusion with green by the dichromics is very +conclusive. The three other test colours, violet, +red, and blue-green, represent both ends of the +spectrum and the neutral point in dichromic cases, +and practically these colours are those with which +most mistakes are made. This test can only be +regarded as supplementary to the Lantern Test.</p> + +<p><span class="pagenum" id="Page_70">70</span></p> + +<p>2. <i>The Pocket Test.</i>—This consists of nineteen +cards, on nine of which are 112 single threads of +wool, and 14 pieces of twisted silk, similar to those +in the Classification Test. These are numbered +consecutively, with the exception of the first +thread of the first four cards, and the last thread +of the next four cards. The end threads of the first +four cards, I to IV, form the tests; they are +Orange, Violet, Red, and Blue-green. There are also +cards on which red, orange, green, blue, violet and +purple, and grey, respectively are to be found. +There are also two special cards marked “Without +Red” and two special cards marked “Without +Green.” (See Fig. 6.)</p> + +<figure class="figcenter illowe27_125" id="i_70"> + <img class="w100" src="images/i_70.jpg" alt=""> + <figcaption class="caption"><p>Fig. 6.</p></figcaption> +</figure> + +<p>Many normal-sighted persons might object to the<span class="pagenum" id="Page_71">71</span> +inclusion of some of the colours on the orange card, +but this card clearly shows the colours which may +be taken as a match. Fine distinctions are not +wanted. The series of colours I have selected and +arranged so as to confuse the colour-blind and +force them to be guided by their colour-perception, +whilst the quantity of colour is amply sufficient +for the normal-sighted to pick out the colours +with the greatest ease. The cards should be +arranged irregularly on a white cloth in a good +light. The two most important tests colours are +the Orange and Violet, Nos. I and II. The person +examined should be asked to point out the shades +of colour similar to No. I (Orange). A piece of +paper rolled to a point should be used for this +purpose. If he do this correctly, he probably +possesses normal colour-perception. If, however, +he match the test with reds or pinks, he is more or +less colour-blind, at best belonging to the pentachromic +class. If, in addition, he match the +Violet test, No. II, with blue, he at least belongs +to the tetrachromic class. The trichromic, in +addition, may match the Blue-green test, No. III, +with brown and grey. The dichromic will match +the Orange test, No. I, with yellow-green and +yellow-brown. Similar mistakes will be made to +those described in connection with the Classification +Test. The examinee should be asked to name +all the colours on one of the cards. He should also +be asked to point out on which of the cards the +four test colours are to be found, and which +contain none of the test colour.</p> + +<p>The examiner should continually change the<span class="pagenum" id="Page_72">72</span> +order of the cards. Most of the varieties of the +colour-blind will be readily detected in this way.</p> + +<p>The special advantages of this test are: (1) The +colour-blind can be ranged definitely in their +proper classes. (2) Central scotoma can be +detected with its aid. (3) The series of colours are +arranged so as to confuse the colour-blind, whilst +the normal-sighted easily match the test colours. +(4) On account of the introduction of different +materials, the relative luminosity and saturation +of colours does not serve as a guide to the colour-blind. +(5) Portability. (6) The wools and silks are +kept clean. (7) An important colour is not likely +to be lost.</p> + +<p>3. <i>The Colour-Perception Spectrometer.</i><a id="FNanchor_13" href="#Footnote_13" class="fnanchor">13</a>—(<i>a</i>) +<i>Description of apparatus.</i>—This instrument is a +spectrometer so arranged as to make it possible to +expose to view in the eyepiece the portion of a +spectrum between any two desired wave-lengths. +In the focal plane of the telescope are two adjustable +shutters with vertical edges; the shutters can +be moved into the field from right and left respectively, +each by its own micrometer screw, and to +each screw is attached a drum, the one being on +the right and the other on the left of the telescope. +On each of these drums is cut a helical slot in which +runs an index, and the drum is engraved in such a +manner that the reading of the index gives the +position in the spectrum of the corresponding +shutter in wave-lengths direct. (See Fig. 9.) Thus +it will be seen that if, for instance, the reading on<span class="pagenum" id="Page_73">73</span> +the left drum-head is 5320 and that on the right +drum-head is 5920, the region of the spectrum from +wave-length 5320 to wave-length 5920 is exposed +to view in the eyepiece.</p> + +<figure class="figcenter illowe22_875" id="i_73-1"> + <img class="w100" src="images/i_73-1.jpg" alt=""> + <figcaption class="caption"><p>Fig. 7.</p></figcaption> +</figure> + +<div class="figcontainer"> +<div class="figsub"> +<figure class="figcenter illowe10_375" id="i_73-2"> + <img class="w100" src="images/i_73-2.jpg" alt=""> + <figcaption class="caption"><p>Fig. 8.</p></figcaption> +</figure> +</div> +<div class="figsub"> +<figure class="figcenter illowe14_375" id="i_73-3"> + <img class="w100" src="images/i_73-3.jpg" alt=""> + <figcaption class="caption"><p>Fig. 9.</p></figcaption> +</figure> +</div> +</div> + +<p><span class="pagenum" id="Page_74">74</span></p> + +<p>(<i>b</i>) <i>Directions for using the instrument.</i>—It +should be used as far as possible with a known +quality and intensity of light. A small oil-lamp +is quite suitable for the purpose. The observer +should first ascertain the exact position of the +termination of the red end of the spectrum, the +left-hand shutter being moved across until every +trace of red just disappears. The position of the +pointer on the left-hand drum is noted, and the +wave-length recorded. The left drum is then moved +so that the shutter is more towards the middle of +the spectrum. The right-hand drum is then +moved, until the pointer indicates the wave-length +recorded as the termination of the red end +of the spectrum. The observer then moves the +left-hand shutter in and out until he obtains the +largest portion of red, which appears absolutely +monochromatic to him, no notice being taken of +variations in brightness, but only in hue. The +position of the index on the left-hand drum is +recorded. The left-hand shutter is then moved +towards the violet end of the spectrum, the right-hand +shutter being placed at the position previously +occupied by the left-hand shutter. In this +way the whole of the spectrum is traversed until +the termination of the violet end of the spectrum +is finally ascertained with the right-hand shutter. +The variation of the size of the patches and the +terminations of the spectrum with different intensities +of light can be noted. The instrument can +also be used for ascertaining the exact position +and size of the neutral patch in dichromics, the +position of greatest luminosity, and the size and<span class="pagenum" id="Page_75">75</span> +extent of pure colours. When it is used to test +colour-blindness, the examinee should first be +shown some portion of the interior of the spectrum, +and then asked to name the various colours which +he sees. In this way he will have no clue to the +colours which are being shown him.</p> + +<p><i>Objections to other tests for colour-blindness.</i>—The +tests which have been proposed for colour-blindness +are very numerous, but some are so +defective that it is rare to detect a single colour-blind +person with them. I have, for instance, +tested men whom I knew to be colour-blind with +certain lanterns with the result that not a single +one was detected. In these so-called tests all the +requirements of a test and facts of colour-blindness +have been neglected. I must, however, refer to +three tests constructed by exceptionally able men, +each with considerable knowledge of the subject. +I refer to the tests of Professor Holmgren, Professor +Stilling, and Professor Nagel.</p> + +<p>All these tests can be passed at the first attempt +without coaching by certain dangerously colour-blind +persons, chiefly varieties not known to the +inventors, but the chief defect of each is that it is +very easy to coach a colour-blind person to pass it. +The surgeon to one of our largest railway companies +told me that when they used Holmgren’s +test they rejected one man in three hundred, but +with my lantern twelve in the same number. All +these three tests are much better tests when the +persons to be examined have not seen them before. +A colour-blind man may make only one mistake, +say for instance, as in a case I examined the other<span class="pagenum" id="Page_76">76</span> +day, with Nagel’s test (last edition), he passes the +test perfectly with the exception of one mistake, +that of calling a grey on one card, green. All he +has to do is to look for some distinguishing mark +on this card in order to go through the test with +the ease and certainty of a normal-sighted person. +It is the same with Stilling’s letters, he has only to +note the letter which he was not able to read and +the appearance of the card. A normal-sighted +man or woman would readily help him. The +confusion of green and grey does not appeal to the +average man as a serious defect, especially when +he sees his friend go through the rest of the test +perfectly. He says to himself, “I suppose he sees a +tinge of green in that grey.” The same man would +rightly regard it as a most iniquitous proceeding +to endeavour to coach his friend through a test +when he had seen him mistake a red for a green +light.</p> + +<p>Holmgren’s test rejects a large number of +normal-sighted persons, as may be seen by the +reports of the Board of Trade; about 50 per cent +of those who appeal are found to be normal-sighted +and to have been rejected wrongly.</p> + +<hr class="r15 x-ebookmaker-drop"> + +<p class="tac fs60">WILLIAM BRENDON AND SON, LTD.<br> +PRINTERS, PLYMOUTH</p> + + +<p class="tac mt6em mb2em ti0"><span class="fs240">Reiner</span> <span class="fs130">and</span> <span class="fs240">Keeler</span>, <span class="fs240">L</span><span class="fs130"><sup>td.</sup></span> + +<p class="tac fs240 ls01em ti0">OPTICIANS</p> +<p class="tac mtb-05 ti0">——————AND——————</p> +<p class="tac fs200 ti0">INSTRUMENT MAKERS</p> + +<p class="ml5em u ti0"><i>MANUFACTURERS OF</i></p> + +<div class="container"> +<div class="content"> +<p class="tal fs140 ti0">The Edridge-Green<br>Colour Perception Lantern</p> +<p class="tal fs140 ti0">The Edridge-Green<br>Classification Test</p> +<p class="tal fs140 ti0">The Edridge-Green<br>Pocket Test</p> +<p>and other</p> +<p class="tal fs140 ti0">Optical and<br>Scientific Instruments</p> +</div> +</div> + +<p class="tac">THE ABOVE COLOUR TESTS ARE CERTIFIED<br> +BY PROF. F. W. EDRIDGE-GREEN</p> + +<p class="ml5em mt3em ti0"><span class="fs140">9 Vere Street,<br> +Cavendish Square,</span> <span class="fs180"><b>London, W.</b></span></p> + +<p class="tac fs80">Telephone: 447 Mayfair.</p> + + + +<div class="footnotes"><h3>FOOTNOTES:</h3> + +<div class="footnote"> + +<p><a id="Footnote_1" href="#FNanchor_1" class="label">1</a> +<i>Journal of Physiology</i>, vol. xli, p. 274.</p> + +</div> + +<div class="footnote"> + +<p><a id="Footnote_2" href="#FNanchor_2" class="label">2</a> +<i>Transactions of the Ophthalmological Society</i>, 1902, p. 300.</p> + +</div> + +<div class="footnote"> + +<p><a id="Footnote_3" href="#FNanchor_3" class="label">3</a> +<i>Journal of Physiology</i>, vol. xli, p. 269.</p> + +</div> + +<div class="footnote"> + +<p><a id="Footnote_4" href="#FNanchor_4" class="label">4</a> +<i>British Medical Journal</i>, 1910, p. 556.</p> + +</div> + +<div class="footnote"> + +<p><a id="Footnote_5" href="#FNanchor_5" class="label">5</a> +<i>Journal of Physiology</i>, vol. xli, p. 226.</p> + +</div> + +<div class="footnote"> + +<p><a id="Footnote_6" href="#FNanchor_6" class="label">6</a> +<i>Nagel. Physiol. des Menschen</i>, vol. iii, p. 107.</p> + +</div> + +<div class="footnote"> + +<p><a id="Footnote_7" href="#FNanchor_7" class="label">7</a> +“Colour Blindness and Colour Perception,” <i>International Scientific +Series</i>, p. 196.</p> + +</div> + +<div class="footnote"> + +<p><a id="Footnote_8" href="#FNanchor_8" class="label">8</a> +<i>Proceedings of the Royal Society</i>, vol. B 82, 1910, p. 458.</p> + +</div> + +<div class="footnote"> + +<p><a id="Footnote_9" href="#FNanchor_9" class="label">9</a> +<i>Proceedings of the Royal Society</i>, vol. B 76, 1905.</p> + +</div> + +<div class="footnote"> + +<p><a id="Footnote_10" href="#FNanchor_10" class="label">10</a> +<i>Transactions of the Ophthalmological Society</i>, 1907, p. 255. <i>Proceedings +of the Royal Society</i>, vol. B 82, 1910.</p> + +</div> + +<div class="footnote"> + +<p><a id="Footnote_11" href="#FNanchor_11" class="label">11</a> +Made by Reiner and Keeler, 9, Vere Street, W.; and Meyrowitz, +1a, Old Bond Street, W.</p> + +</div> + +<div class="footnote"> + +<p><a id="Footnote_12" href="#FNanchor_12" class="label">12</a> +<i>International Scientific Series.</i> Kegan Paul & Co., 1909.</p> + +</div> + +<div class="footnote"> + +<p><a id="Footnote_13" href="#FNanchor_13" class="label">13</a> +Made by A. Hilger, 75a, Camden Road, London, N.W.</p> + +</div> +</div> + +<div style='text-align:center'>*** END OF THE PROJECT GUTENBERG EBOOK 75519 ***</div> +</body> +</html> + diff --git a/75519-h/images/cover.jpg b/75519-h/images/cover.jpg Binary files differnew file mode 100644 index 0000000..17884da --- /dev/null +++ b/75519-h/images/cover.jpg diff --git a/75519-h/images/i_18.jpg b/75519-h/images/i_18.jpg Binary files differnew file mode 100644 index 0000000..2b4697c --- /dev/null +++ b/75519-h/images/i_18.jpg diff --git a/75519-h/images/i_20.jpg b/75519-h/images/i_20.jpg Binary files differnew file mode 100644 index 0000000..a1fbfd6 --- /dev/null +++ b/75519-h/images/i_20.jpg diff --git a/75519-h/images/i_54.jpg b/75519-h/images/i_54.jpg Binary files differnew file mode 100644 index 0000000..e8ab104 --- /dev/null +++ b/75519-h/images/i_54.jpg diff --git a/75519-h/images/i_55.jpg b/75519-h/images/i_55.jpg Binary files differnew file mode 100644 index 0000000..b53a8c2 --- /dev/null +++ b/75519-h/images/i_55.jpg diff --git a/75519-h/images/i_68.jpg b/75519-h/images/i_68.jpg Binary files differnew file mode 100644 index 0000000..b025b9e --- /dev/null +++ b/75519-h/images/i_68.jpg diff --git a/75519-h/images/i_70.jpg b/75519-h/images/i_70.jpg Binary files differnew file mode 100644 index 0000000..5d77b7d --- /dev/null +++ b/75519-h/images/i_70.jpg diff --git a/75519-h/images/i_73-1.jpg b/75519-h/images/i_73-1.jpg Binary files differnew file mode 100644 index 0000000..e4a95ea --- /dev/null +++ b/75519-h/images/i_73-1.jpg diff --git a/75519-h/images/i_73-2.jpg b/75519-h/images/i_73-2.jpg Binary files differnew file mode 100644 index 0000000..39f57e7 --- /dev/null +++ b/75519-h/images/i_73-2.jpg diff --git a/75519-h/images/i_73-3.jpg b/75519-h/images/i_73-3.jpg Binary files differnew file mode 100644 index 0000000..4c8793f --- /dev/null +++ b/75519-h/images/i_73-3.jpg |
