594
THE NEW ZEALAND GAZETTE.
[No. 24

having a moment before seen others looking for and arranging them. He will make the same characteristic mistakes; but the normal observer, on the other hand, will generally accomplish his task much better and more quickly after having seen how it has to be done.

The coloured plate shows the test-colours, and some of the mistakes likely to be made by colour-blind people. The colours in the plate are of two characters:—

1. The colours for samples (test-colours)—that is, those which the Examiner presents to the person examined; and,

2. The “confusion-colours”—that is to say, those which the colour-blind may select as matches with the sample.

The first are shown on the plate as horizontal bands, and are distinguished by Roman numerals (I., II.a, and II.b); the second as vertical bands under the test-colours, and are distinguished by Arabic figures (1, 2, 3, &c.).

As to the similarity between the confusion-colours of the plate and the wools which the colour-blind take from the heap, reliance must be placed simply on the hue, and not their brightness or degree of colour-saturation. The confusion-colours shown in the plate are only to illustrate the mistakes which the colour-blind may make, and for this purpose they serve perfectly. Having made this explanation, we can pass directly to the test itself. The following are the directions for conducting it, and for making a diagnosis from the results:—

Test I.—The green test-skein, which is labelled Test No. I. in the bundle, is exhibited to the candidate. This sample is the palest shade (the lightest) of very pure green, which is neither a yellow-green nor a blue-green to the normal eye, but fairly intermediate between the two, or, at least, not verging upon yellowish-green.

Rule.—The examination must continue until the examinee has placed near the test-skein several other skeins of the same colour, or else, with these or separately, one or more skeins of the class of “confusion-colours” such as 1 to 5 in the plate, or until he has sufficiently proved that he can easily and unerringly distinguish the confusion-colours, or, else has given unmistakable proof of a difficulty in accomplishing it.

Diagnosis.—An examinee who places with the test-skein “confusion-colours” such as 1 to 5—that is to say, finds that they resemble the “test-colour”—is colour-blind, whilst if he evinces a manifest disposition to do so though he does not absolutely do so, he has a feeble chromatic sense or sense of colour.

Remark.—We might have taken more than five colours for “confusion”; but we must remember that we are not taking into consideration every kind of defective colour-sense.

Test II.—The pink or light-purple skein, which is labelled No. II.a, is shown to the examinee. The colour is midway between the lightest and darkest. It only approaches that given as II.a of the plate, as the colour of the wool is much more brilliant and saturated, and bluer.

Rule.—The trial must be continued until the examinee has placed all or the greater part of the skeins of the same colour near the test-skein, or else, together or separately, several skeins of the “confusion-colours,” such as 6–9. If he is colour-blind he will probably select either the light or deep shades of blue and violet, especially the deep (6 and 7), or the light or deep shades of one kind of green or grey inclining to blue (8 and 9).

Test III.—The red skein labelled No. II.b is presented to the examinee. It is necessary to have a vivid-red colour, like the red flag used as signals on railways. The colour should be that of II.b of the plate, rather towards yellowish-red.

Rule.—This test should be continued until the person examined has placed beside the test-skein the greater part of the skeins belonging to this hue, or else several “confusion-colours” (10–13).

Remark.—Every case of comparatively complete colour-blindness does not always give precisely the same mistakes. Instances occur of persons who are not completely colour-blind, or of completely colour-blind persons who have been practised in the colours of signals, and who endeavour not to be discovered. They usually confound at least green and brown, but even this does not always happen.

Monochromatic Vision.—The absence of every colour-sensation except one will be recognised by the confusion of all the hues, which will appear to be of the same intensity of light or brightness.

Dr. Joy Jeffries, in his book on colour-blindness, gives a translation of Holmgren’s special directions for conducting the examinations. The examinations to which Holmgren refers were for employés on the Swedish railways, but the remarks which follow are applicable to examinations for officers and seamen in the mercantile marine.

Special Directions for conducting the Test.

The method plays an important part in an examination of this kind, not only from the principles upon which it rests,

but also from the manner in which it is used. The best plan for directing how to proceed is by oral instructions and de visu, but here we are obliged to accomplish this by description. Now, this is always defective in some respects, especially if we wish to be brief. What has been said would evidently suffice for an intelligent and experienced physician; but it may not be superfluous to enter still further into detail to provide against any possible difficulties and loss of time. The object of the examination is to discover the nature of a person’s chromatic sense, or sense of colour. Now, as the fate of the candidate and that of others depend upon the correctness of the judgment pronounced by the Examiner, and as this judgment should be based upon the manner in which the candidate stands the trial, it is of importance that this trial should be truly what it ought to be, a trial of the nature of the chromatic sense, and nothing else—an end that will be gained if our directions are strictly followed. It is not only necessary that the Examiner should carefully observe them—which does not seem to us difficult—but that he also should take care that the individual examined does thoroughly what is required of him. This is not always as easy as one might suppose. If it were only required to examine people familiar with practical occupations, and especially with colours, and with no other interest connected with the issue of the examination than to know whether they are colour-blind or not, the examination would be uniform and mechanical; but it is required to examine people of various degrees of culture, all of whom, besides, have a personal interest in the issue of the examination. Different people act very differently during the examination for many reasons. Some submit to it without the least suspicion of their defect; others are convinced that they possess a normal sense. A few only have a consciousness, or, at least, some suspicion, of their defect. These last can often be recognised before examination. They will keep behind the others, and attentively follow the progress of the trial, and, if allowed, will willingly remain to the last. Some are quick, others slow. The former approach unconcernedly and boldly, the latter with over-anxiety and a certain dread. Some have been, perhaps, already tested, and have practised in preparation for the trial; others have never been familiar with colours. Among those already tested some may be colour-blind. Some of these latter are uncertain about their colour-vision, and act with great care; whilst others, again, having been practised in distinguishing signals, conclude that their colour-sense is perfect. They make the trial quickly and without thought, of course regularly making the mistakes characteristic of their special form of colour-blindness.

The majority, however, desire to perform their task as well as possible—that is, to do what the normal eye does. This, of course, assists in testing them, providing it does not lead to too great care, as then the testing is more difficult, the trouble being that much time is wasted.

Only a very small part have a contrary desire—namely, to pass for colour-blind, though normal-eyed. We will speak of these later, and now only concern ourselves with those who stand the test in good faith with the desire to appear normal, though, perhaps, they are colour-blind.

The trial generally goes on rapidly and regularly. We will only mention those hindrances and peculiarities which most frequently occur. The Examiner must watch that no mistake is made from not understanding. The names of the colour need never be used, except to ascertain if the name hides the subjective colour-sensation, or to find the relation between the name the colour-blind employs and his colour-perception.

The person examined who thinks more of names than the test itself (this being generally a sign of school-learning) selects not only the wools of the same hues—that is, those of the same colour to his eye—but all which generally have the name of this colour—for instance, in the first test, I., not only the green like the sample, but all that are green; and with the second test, not only the purple (and what are generally called red), but all which look reddish, scarlet, cinnabar, or sealing-wax red. This is of no importance, for those who only do this have scarcely such defective chromatic sense as that with which we are concerned.

Under any circumstances it is better to correct the mistakes just mentioned, when arising from misunderstanding, and it is even necessary, in reference to the mistakes we explained might occur with the first test. It might be said that it was sufficient if the examined confounded the test-colour with green only; that it was indifferent whether he distinguishes carefully between the various kinds of green. But, in fact, this is not so unimportant. We must give full weight as to whether the confusion arises from misunderstanding, or lack of practice with colours; or, finally, from a true chromatic defect. To include all that is green would render the test tedious and unpractical. In fact, no little judgment has been exercised in the selection of the very lightest shade of the green proposed as a test-colour, for it is exactly what the colour-blind most readily confounds with