The following interesting cases are of a character forming a connecting link between the two classes of achromatopsy. The first is related by D'Hombres Firmas.§ Count -- of Alais, aged thirty -eight, married, and the father of a family, possessed excellent vision in every repeat, except the perception of colours ; but yellow, and the shades be tween black and white, were the only tints lie could recognise. On a number of dif ferent roses being placed in his hands, he merely saw that white flowers were brighter than purple ; yellow flowers he distinguished, but red, blue, violet, and white blossoms all appeared more or less dark though he dis tinguished the yellow centres. This gen tleman was fond of geology, but found it im possible to judge of the colours which marked various formations in the map of M. Dumas. Lacustrine formations and the lias were the only ones which he distinguished, all the others appearing to him tinted in grey; and he would have confounded them together, if his excellent sight had not enabled him to follow the dotted lines and letters by which they were indicated. He drew with taste in crayon, Indian ink, and sepia ; but only on one occasion attempted a scene in colours, of a peasant and a bouquet of flowers. The re sult was so very unsatisfactory to ordinary eyes, that he was not tempted to repeat the experiment.
The second case has been recorded by Dr. Deconde.* A soldier applying for his discharge on the ground of the formation of cataract, attracted particular attention on account of the cyanic colour of his sclerotica ; and on investigating his power of distinguishing co lours, it was found that all those of the spec trum were confounded in two fundamental hues, yellow and blue. Dark red, bright red, rose, orange, yellow, green in which yel low predominated, and grey white, all ap peared as different shades of yellow : whilst blue, green, and white with a blueish shade, were perceived as blue. All the very deep colours were regarded as black, and all the very light ones had a whitish appearance, though the man did not seem to have cogni zance of white, properly so called. Light, de composed by a prism, appeared to him of uni form blue. His sight was feeble and easily fatigued. Numerous trials always led to the above results.
Class II. (Polychronzatic Daltonism of Wartmann.)—This form includes the vast ma jority of cases of insensibility to colours, and presents a very remarkable diversity of phe nomena. The colour, which, of all others, is the stumbling-block, is lilac, and next to it rose, indigo, and violet; on the other hand, yellow and blue are most common13 recog nised. A very general form is that first de scribed by the illustrious Daltont, who has given his name to the affection ; and the following are the chief features of his case. He was not conscious of any peculiarity of vision until the age of twenty-six, when, a dis cussion arising as to the colour of the flower of Geranium 2onale, it was discovered that he and his brother differed materially from other people in their ideas upon the point. About
two years afterwards he entered upon an in vestigation of the subject, and the following are the principal results at which he arrived. The solar spectrum appeared composed of three colours, yellow, blue, and purple, the red being little more than a shade or defect of light. Orange, yellow, and green were shades of yellow, whilst green and blue were strongly contrasted. Of ordinary colours, crimson and dark blue were identical ; the colour of a florid complexion being a dull opaque blackish blue, upon a white ground ; blood seemed bottle green ; the lime of a laurel leaf was a good match for a stick of sealing wax ; and the back of the leaf an swered to the lighter red of wafers. Green baize appeared a dark brownish red; and a light drab was not to be distinguished from a light green ; browns were very diversified, some having a great affinity for gredn, others for red; pink appeared sky blue by daylight, but assumed an orange or yellowish appear ance by candle light. Dalton believed that the peculiarity in his vision was caused by the vitreous humour of his eyes having a blue tint : to this point reference will hereafter be made.
According to Professor Wartmann, the following are the most common confusions of colour, ranged in order of their frequency : — Putting aside the differences in the bril liancy of the tints, it is found that the follow ing numbers express how many times each of those tints is proportionally seen without error.
Wartmann has given * a very interesting account of his experiments on the vision of Louis D—. This individual did not per ceive any great difference between the colour of the leaf and that of the ripe fruit of the cherry ; he confounded that of a sea-green paper with the scarlet of a riband placed close to it. The flower of the rose seemed to him greenish blue, and he called the ash colour of quick lime light green. The appearances presented by a solar spectrum were as follows, —the coloured bands, brilliant and distinct, extended a length of about 0.102'. D perceived four colours only, blue, green, yel low and red. He limited the blue part exactly to the space occupied by the violet, indigo and blue : he called the green and yellow bands, less an interval of 0.002' towards the orange, green ; he called that band of and a fraction of the red 0.012' in breadth, yelloW; lastly, the remaining of red appeared to him of a red difficult to define. By refracted light the results were nearly the same, thirty seven plates of glass exhibiting only four different colours in various intensities.