VISION. 



1453 



ally the expression "Daltonian" may be used 

 for the sake of brevity. 



Modifications of insensibility to colours 

 exist in every degree, and in the minor shades 

 are so frequent as to be almost proverbial 

 with reference to the male sex ; indeed, if 

 twelve men, taken at random, were shown a 

 minuter of ribands of the more delicate 

 colours, a diversity of opinion would almost 

 certainly arise as to the appropriate names. 

 The number of persons who cannot distinguish 

 certain colours is considerable ; but the defect 

 is seldom known to others, those who are con- 

 scious of their imperfection being desirous^ of 

 concealing it, and some perhaps, not being 

 aware of it till accident leads to its discovery. 

 In every case that lias fallen under our notice, 

 there lias been reluctance to submit to ex- 

 amination, from the fear of ridicule ; and 

 indeed it is difficult to repress a smile when a 

 person is seen to match green and scarlet to- 

 gether, or crimson and dark blue, and earnestly 

 protest that the colours are absolutely iden- 

 tical. The nearest approach to this condition 

 in the healthy eye" and a test by which the 

 embarrasment of Daltonians may be judged of, 

 is the difficulty of distinguishing between blue 

 and green by candlelight ; a difficulty which 

 every one must have experienced. Analogous 

 to this defect of the organ of vision, is that 

 better known, because more evident, insensi- 

 bility of the organ of hearing, whereby many 

 persons are utterly unable to detect the differ- 

 ences between musical notes, or, as pointed 

 out by Dr.Wollaston, their ears maybe abso-^ 

 lutely insensible to sounds at one extremity of 

 the scale. Sir David Brewster remarks* that, 

 although his own hearing is perfect and each 

 ear equally acute for all ordinary sounds, yet 

 one of them is absolutely deaf to the chirp of 

 the cricket, while the other hears it distinctly. 

 Dr. Pliny Earle has published t a remarkable 

 illustration of the imperfection of the two 

 senses in conjunction. " The whole family 

 (says he) of which the chart has been ex- 

 hibited, is probably no less generally charac- 

 terised by a defective musical ear than an 

 imperfect appreciation of colours. Several of 

 the individuals comprised in it are utterly inca- 

 pable of distinguishing one tune from another. 

 * * A gentleman who has the general defect 

 under discussion, and whose case is included 

 in the thirty-one herein mentioned, is a well- 

 known professor in one of the Metropolitan 

 Medical Schools of the United States. In 

 him the total inability to discriminate between 

 musical sounds is coexistent with the defec- 

 tive perception of colour * * Another 

 of the gentlemen whose case of defective per- 

 ception of colours is herein noticed, is gene- 

 rally acknowledged as one of the first and 

 greatest of American poets now living. He 

 also is unable to distinguish one tune from 

 another ; yet his poetry is not deficient in the 

 requisites of perfect cadence, harmony, and 

 rhythm." 



* Philosoph. Mag. vol. xxv. p. 130. 

 f American Journal of Medical Sciences, vol. 35. 

 p. 347. 



It has been remarked by Wartmann as a 

 curious fact, that in no ancient author is there 

 any passage which can be referred to the 

 subject of achromatopsy, and that the nume- 

 rous travellers who have traversed the old and 

 new world are equally silent in this respect. 



As to the relative frequency of achroma- 

 topsy, Seebeck states that five out of forty 

 youths who composed the two upper classes 

 in a gymnasium at Berlin, were affected with 

 it, and Prevost has declared that the pro- 

 portion of this imperfect vision to perfect 

 vision, is as one to twenty. It is true that 

 Chelius and Chevreul entertain a very op- 

 posite opinion, but the balance of authority is 

 decidedly against them. 



This affection is often hereditary, and is 

 found in some families to a remarkable extent. 

 It sometimes occurs in successive generations, 

 of which a remarkable instance has been pub- 

 lished by M. Cunier*, and at other times it ap- 

 pears in alternate generations, descending far 

 more frequently on the maternal side than the 

 paternal. In the case of Mr. Milne, recorded 

 by Dr. Combef, the maternal grandfather was 

 affected with Daltonism, also his two brothers 

 and a second cousin. In that of a child related 

 by Dr. NichollJ the maternal grandfather and 

 several of his brothers were similarly affected ; 

 such was also the case with two young men 

 mentioned by Dr. Cornaz.$ They were the 

 offspring of the same mother but by different 

 fathers, and in both, achromatopsy existed to 

 a marked degree. But the most striking 

 illustration of the hereditary character of this 

 defect has been recorded by Dr. Pliny Earle ||, 

 and it is so remarkable that -we give it in 

 his own words. " My maternal grandfather 

 and two of his brothers were characterised 

 by it, and among the descendants of the first 

 mentioned, there are seventeen persons in 

 whom it is found. I have not been able to 

 extend my inquiries among the collateral 

 branches of the family, but have heard of one 

 individual, a female, in one of them, who 

 was similarly affected.* * * Nothing is known 

 of the first generation (of five) in regard to 

 the power of perception of colours. In the 

 second, of a family consisting of seven 

 brothers and eight sisters, three of the 

 brothers, one of whom, as before mentioned, 

 was the grandfather of the writer, had the 

 defect in question. In the third generation, 

 consisting of the children of the grandfather 

 aforesaid, of three brothers and foursisteis, 

 there was no one whose ability to distinguish 

 colours was imperfect. In the fourth genera- 

 tion, the first family includes five brothers 

 and four sisters, of whom two of the former 

 have the defect. In the second family there 

 was but one child, whose vision was normal. 

 In the third there were seven brothers, of 

 whom four had the defect. In the fifth, seven 

 sisters and three brothers, of all of whom the 



* Annales d'Oculistique, torn. i. p. 417. 



t Transactions of Phrenological Society, p. 222 



t Med. Chir. Trans, vol. vii. p. 477. 



Annales d'Oculistique, torn, xxiii. p. 43. 



|| Op. cit. p. 34'J. 



