consequence of the many blunders he committed in the combination of his reds and greens. Upon my directing his attention not long since to a very brilliant carpet, having a bright scarlet ground, with vivid green fern-leaves running over it, he said he could see no difference except in the warmth of tone of the red over the green. I have repeatedly examined his eyes with the ophthalmoscope without observing any departure from the normal condition, except a small difference in the colour of the fundus; the choroid has less blood circulating in it, and the pigment-coat is certainly much paler. But this must be taken with some modification, as the irides are brownish, scarcely hazel: in every other respect the sight is nearly normal, as may readily be surmised, from his successful career as a sculptor. An only sister, it should be mentioned, paints to perfection.

From other instances on record, it would seem that colourblindness is frequently compensated for by the greater exactness with which distant as well as near objects may be perceived, and this, too, in a comparatively obscure light. We find in the "Glasgow Medical Journal," vol. ii., a case of the kind with some valuable remarks by the individual himself. "All objects whatever, when viewed at a distance, lose their local colouring, and assume more or less of a pale azure blue tinge, which painters term the colour of the air: this is interposed between myself and a distant object. No colour contrasts to me so forcibly with black as this azure blue; and as you know that the shadows of all objects are composed of black, the forms of objects which have acquired more or less of this blue tint from being distant become defined and marked by the possession of shadows which are invisible to me in the more highly coloured objects in the foreground, and which are thus left comparatively confused and shapeless masses of colour. So much is this the case with me when viewing a distant object, as to overcome the effect of perspective, and the shading in the form and the garments of human beings at some distance from my eye is often so predominant, and marks them out so distinctly, as to overcome the effect of diminution of size; and although I see the object most distinctly, I am unable to tell whether it be a child near me or a grown-up person far off."

Both Professor Wartmann and Dr. Wilson examined and tested individuals who corrected by the touch erroneous judgments which they formed regarding colours. A case of the kind came under my own observation which I shall presently relate; and I know and have met with very many instances in the totally blind able to distinguish every variety of colours by the delicacy of the sense of touch: they tell me there is a

sensible difference in the degree of heat conveyed to the point of the finger.*

The fact that a difference of tint is recognized, although the eye of the colour-blind person does not appreciate any difference of colour, as red and green, when compared together, and that every one is educated to call things by certain names, whether he understands the meaning or not, may help to explain the slowness with which this defect is discovered; and again, that the report of every case is rendered hopelessly imperfect from the impossibility of subjecting the eye to the test of colour.

"I

In the "Philosophical Transactions for 1859," Mr. W. Pole, a well-known civil engineer, thus describes his own case: was about eight years old when the mistaking a piece of red cloth for a green leaf betrayed the existence of some peculiarity in my ideas of colours; and as I grew older continued errors of a similar kind led my friends to suspect that my eyesight was defective; but I myself could not comprehend this, insisting that I saw colours clearly enough, and only mistook their names. I was articled to a civil engineer, and had to go through many years of practice in making drawings of the kind connected with this profession. These are frequently coloured, and I recollect often being obliged to ask in copying a drawing what colours I ought to use; but these difficulties left no permanent impression, and up to a mature age I had no suspicion that my vision was different from that of other people. I frequently made mistakes, and noticed many circumstances in regard to colours which temporarily perplexed me. I recollect in particular having wondered why the beautiful rose light of sunset on the Alps, which threw my friends into raptures, seemed all a delusion to me. I still, however, adhered to my first opinion, that I was only at fault in regard to the names of colours, and not as to the ideas of them; and this opinion was strengthened by observing that the persons who were attempting to point out my mistakes often disputed among themselves as to what certain hues of colour ought to be called." At length Mr. Pole when about thirty years of age committed a glaring blunder, and this circumstance led him to make an investigation of his case, which ended in his discovering that he was colour-blind.

All who have investigated the subject of colour-blindness

* Professor Tyndall enters fully into all these matters in his work on "Heat as a Mode of Motion" (reviewed in the present number). The eighth chapter treats of the relations of light, heat, and colour, and will be found deeply interesting to those who have read this article, and desire further information on the subject.-ED.

agree that in the greatest number of cases it is not a disease, but rather a remarkable type of vision. It is known, however, that the peculiarity exists sometimes as a matter of degree, and that an abnormal sensation of colour may be received, but of so short a duration and corrected spontaneously as to be a source of little inconvenience, and even passes unnoticed. But as many important facts in connection with the subject have come to light, it is now made essential, and very properly so, for every driver or guard of the railway train to pass an examination as to his power of perceiving and distinguishing different coloured signals used on railways. Dr. Wilson goes further, and says: "It admits of a question whether the demands of public safety would be best met by excluding colour from railway and ship signals, or by excluding the colour-blind from the office of signalmen." Red and green lamps are employed as signals at sea, as well as on railways, and many appalling accidents, no doubt, have been occasioned by mistaking the colour exhibited both on sea and land.

A mistake in colour may arise from the fact that the sensation can only be prolonged for a very limited time. Thus, whenever any one looks fixedly at a bright object placed on a surface of a dark tint, and then closes his eyes, or transfers them suddenly to another ground of a lighter colour, he immediately perceives an image presenting a colour complementary to the one last observed. This arises, also, when the eyes have been fatigued by the prolonged observation of a coloured and very bright object, as a coloured light, and then suddenly turned to look at another object of a different colour; or when the eyes are fatigued by overwork and hours of watching. Many remarkable cases are on record where coloured vision has been suddenly produced. The particulars of a somewhat remarkable case lately excited some attention, and a medicolegal question of importance was raised. The sufferer, a

corn-dealer, brought an action against a railway company for compensation, inasmuch as that after the accident every thing appeared yellow, and all qualities of flour, therefore, were alike in colour. The evidence chiefly depended upon the man's own statement, as it appeared the eyes were carefully examined, and yet none of the medical witnesses could give any explanation as to the cause of the yellow vision. The jury, however, awarded £1,200 damages; and as a certain amount of coloured vision is not unfrequently found to be associated with paralysis, it is not difficult to believe the retina may have been partially paralysed by the severe shock received in this railway collision.

But whether we regard colour-blindness as only a curious physical phenomenon, simply a defect, or as a positively

abnormal condition in some one or more of the structures of the eye, it may be truly said we know so little concerning its true nature, that I need offer no apology for the few remarks I am about to add upon it. As I have often met with it associated with actual disease, and since by the invention of the ophthalmoscope we are now enabled to observe many very curious changes in the internal eye before unrecognized, it is not improbable by its aid we may ultimately discover some structural differences in the eyes of the colour-blind. And if the proposition be well founded that the colour of the internal membranes of the eye must affect its perception of colours, then the choroid, which is the most fully coloured of the tunics, and the one most liable to vary in extent and depth of coloration, must have a very important influence on colour-vision. Now, in the few cases that I have had the opportunity of examining, I noticed a considerable difference both in the quantity of pigmental colouring matter, in the size of the vessels, and in the amount of blood circulating in the eye. This will be seen by any one not conversant with these matters, upon comparing the size, and perfection of the vessels in the otherwise sound eye represented in figure 1 with that of figure 2, a drawing made from an eye in a state of disease, the person having also been colour-blind prior to the loss of sight. This, however, I am ready to admit, may prove to be the exceptional and not the general condition of the eyes in the colour-blind; further investigations alone will settle this point. The seat or cause of the defect probably lies altogether beyond our reach; but whatever we can learn concerning it is certain to be of service in determining the extent to which we may hope to cure or alleviate this affection of sight.

The first case of colour-blindness that fell under my notice was that of my late talented friend, Mr. Angus Reach, whose untimely death has been so much and so justly lamented. He was incapable of distinguishing green, and only partially so red. With him both were nearly the same. The former would sometimes appear more of a pink than even red. He had altogether but a very poor conception of the primary colours. This I detected on one occasion when endeavouring to demonstrate the gradation of beautiful colours displayed by some objects made to depolarize light when placed on the stage of my microscope. After a long endeavour to convince him of the fact, as he could see nothing wonderful in it, I discovered that he was unable to name the colours correctly; and he then told me he had always been indifferent about them. To prevent error he had been accustomed always to avoid describing them, except in relatively as light and shadow, or black and white. He remarked of the vin-ordinaire of France, that

to him it appeared so like ink that he once found himself endeavouring to write with it. He saw no red in it.

At this time, unfortunately, my attention was not so much drawn to ophthalmic disease as it has been since, and I omitted to make such an investigation of this remarkable affection which in one so fully capable of affording accurate information as to the phenomena observed would have been so valuable. Very soon after he was attacked with the first symptoms of softening of the brain, which gradually progressed during the two years his life was prolonged.

It has since several times occurred to me that the defective condition of sight might have been connected with the early development of the disease in the brain. The extreme condition of colour-blindness in which I found Mr. Reach's eyes must have been a progressive aggravation, for otherwise it is most probable more notice would have been taken of it than seems to have been the case. Indeed it might have been induced as the first symptom of an overworked brain, as I have had opportunities since of observing instances of colourblindness arising from general disturbance of the system, and disappearing as this was corrected and relieved.

In another case, the fundus of the eyes upon examination were seen to be very pale; the defect gradually yielded to proper treatment. The gentleman, Mr. Raith, first noticed many peculiar appearances when looking at green leaves, chiefly so if growing with grass; then all appeared elongated and serrated. Even the leaves of trees a willow-tree in particular-were not only indistinctly seen, but were very much serrated. Red flowers of most kinds could only be distinguished by their form from leaves; the exception to this was when they were globular in their form, as the dahlia.

Mr. W. Butcher was early put to the carpet trade, and after a short time he discovered some defect of sight which ultimately proved to be colour-blindness. By close observation he made himself well acquainted with the proper names of colours, and so kept his defect from those about him. By educating the eye to the peculiar warmth imparted when all the colours in carpets were said to harmonize, he was enabled to raise himself to the position of a salesman in a large house of business, and ultimately became travelling salesman. He has four brothers living, all of whom are colour-blind. Taking up the prismatic colours, he could distinctly see the line of demarcation between them, but confounded purple and crimson, pink and blue, red and green; and on placing before him a series of reds, scarlets, greens, and browns, he said, "They are all a mass of confusion, and it is totally impossible for me to distinguish one from the