VISION. 



14-57 



pearecl as a blue grey, rose colour dirt)' white ; 

 orange, pure yellow ; apple green, yellow ; 

 lilac, blue ; violet, grey. There was no un- 

 usual appearance in his eyes, but he saw most 

 perfectly in the evening. 



Dr. Sommer* has described his own case 

 thus. Blue can always be distinguished from 

 yellow, br'ght blue from green, and deep red 

 from black, but green and dark blue are 

 often confounded. Yellow, black, and de- 

 ckled blue are the fundamental colours. If 

 he holds a leaf of a tree and a stick of red 

 sealing-wax side by side he recognises dis- 

 tinctly the difference in intensity between 

 the two colours, but cannot affirm which is 

 green or which red : rather decided blue 

 anil rather intense red bear a great re- 

 semblance; blue is confounded with red, 

 green with brown, brown and orange with 

 bright brown. As to crimson, lilac, purple 

 and deep scarlet, they are colours of which 

 he cannot form even an idea. He one day 

 met a lady wearing a blue bonnet ornamented 

 with red roses, but could scarcely distin- 

 guish any difference between the two. On 

 another occasion when walking out it began 

 to rain. " Then (says he) a crowd of red um- 

 Lrellas displayed themselves, and I compared 

 the colour to the azure of the sky." The 

 rainbow appeared to him composed of blue 

 and yellow ; he knew that there were shades, 

 but could not satisfactorily discern them. 



The case of the late Mr. Tioughton was 

 examined by Sir John Herschell and Sir D. 

 Brewster, and it was ascertained that he saw 

 the red space yellow ; hence according to the 

 \iews of Sir D. Brewster, he saw a space con- 

 taining much yellow, and little blue, the red 

 light being as it were absorbed in consequence 

 of the retina being insensible to its action. Sir 

 D. Brewster goes on to sayf, " If this be the 

 case there must have been a diminution of light 

 in the red space seen by Mr. Troughton, and I 

 am persuaded from the experiments I made 

 upon his eyes that this was the case ; but whe- 

 ther it was to -the extent of the total defalcation 

 of the red rays, I will not venture to assert. 

 But it is not necessary that it should be so ; 

 the defective perception of red light may be 

 accompanied with a more acute perception of 

 the other colours, in a mariner analogous to 

 what takes place in the chemical spectrum, 

 where the removal of the red rays produces 

 an increased action of the rays that are left." 

 Sir D. Brewster, adds that he has long been 

 of opinion that the retina receives a more 

 powerful luminous impression from yellow 

 light than from the pure white light of which 

 this yellow forms but a part. 



Persons affected with achromatopsy not 

 only see well in deep gloom, but their vision 

 of distant objects is particulaily sharp, from 

 the azure blue of the atmosphere presenting 

 the strongest possible contrast to black. One 

 intelligent person saysj, " So much is this the 



* Graefe und Walthers, Journal fur Chirurgie, Bd. 

 v. Heft i. S. 135. 



t Phil. Mag. vol. xxv. p. 139. 



j Glasgow Medical Journal, vol. ii. p. 12. 



VOL. IV. 



case -with me when viewing a distant object 

 as to overcome the effect of perspective ; ar.d 

 the shading in the form and garments of 

 persons at a distance is often so predominant 

 as to overcome the effect of diminution in 

 size ; and although, I see the object most dis- 

 tinctly, I am unable to tell whether it be a 

 child near me or a full-grown person at a 

 distance." 



Daltonians endeavour to obviate the an- 

 noyances arising from their infirmity by 

 taking some standard colours or shades as 

 points of comparison, as for instance the 

 green of grass ; they also bring the sense of 

 touch to their assistance, and are enabled by 

 tht se means, united with close attention, to 

 avoid many errors ; but nevertheless they feel 

 repugnance to express an opinion upon colours 

 Nun-congenital Achromatopsy. This though 

 quite distinct from t'/iriij)t>ia, is generally a 

 morbid symptom, and might easily be con- 

 founded with it. It is to be borne in mind 

 that in certain cases of chrupsia objects ap- 

 pear tinged with colours foreign to them ; 

 a general officer for instance saw all v\hite 

 objects of a deep orange colour at certain 

 times of the da}-, and to a lady they appeared 

 of a bright blue*; but in such cases all 

 objects are tinged with a prevailing tint or 

 it is confined to those which are white, 

 coloured objects being properly recognised. 

 In achromatopsy one or more colours are 

 effaced, and the individual is no longer cog- 

 nizant of them. 



Permanent Achromatopsy. A bootmaker 

 in Paris f , was attacked with amaurotic 

 amblyopia, which followed suppression of the 

 cutaneous exhalation. It was accompanied 

 with rheumatic pains, and there was at first 

 irritation of the retina, but this subsided, 

 leaving the siaht imperfect. The patient, 

 howe\er, assured M. Szokalski that he had 

 possessed a full perception of colours until 

 after a copious bleeding from the arm. From 

 that time he could only discern white, black, 

 and grey, and could not distinguish an engrav- 

 ing from a coloured print. He one day bougjit 

 a piece of yellow morocco leather by mistake 

 for a white piece, and when examined by M. 

 Szokalski, he could not distinguish any co- 

 loured patterns which were exhibited to him. 

 Dr. Mackenzie thus writes : " I always con- 

 sidered this affection as a congenital one, till I 

 was consulted by a man who had gradually 

 become subject to it. He was by trade an 

 ornamental painter, and could judge at one 

 time perfectly of colours. His right eye was 

 affected with mydriasis when he called upon 

 me, and there was incomplete amaurosis of 

 both eyes, so that he could no longer read a 

 common type. On trying him I found he 

 mistook red and green. The use of spirits 

 and tobacco was probably the cause of the 

 affection of sight in this individual.''^ 



* Collections from the unpublished medical writ- 

 ings of C. H. Parry, M.D. vol. i. 



t Ann. d'Oculistique, torn. iii. p 200. 



j Practical Treatise 011 Diseases of the Eye, 3rd 

 edition, p. 7'J9. 



5 A 



