# 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." It has been remarked by Warttnann 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 Chevrcul 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. Combet, the maternal grandfather was affected with Daltonism, also his two brothers and a second cousin. In that or a child related by Dr. Nicholl $ 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 II, 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 tha defect in question. In the third generation, consisting of the children of the grandfather aforesaid, of three brothers and four sisters, 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 vision is perfect in regard to colour. In the sixth, four brothers and five sisters, of whom two of each sex have the defect. In the seventh, two brothers and three sisters, both of the former having the defect. In the eighth, there was no issue, and in the ninth there a e two sisters, both of them capable of appreciating colours." Of the fifth genera tion " the defective perception has hitherto been detected in but two of the families. In one of them, consisting of three brothers and three sisters, one of the brothers has the defect, and in the other, a male, an only child, is similarly affected." Sex exercises a considerable influence on the occurrence of achromatopsy ; of the thirty-one cases mentioned by Dr. Earle. twenty-seven were males and four females, and the result of upwards of two hundred cases shows that as a general rule the propor tion of males is nine tenths of the whole. A very remarkable instance has however been published by M. Corder*, where achroma topsy occurred in five generations of one family, there being thirteen cases, and all females ; but this stands alone as a notable exception to the general rule. If it be true that the works of the needle are the means of perfecting a delicacy in the judgment of tints, and in women the organ of colour is more developed than in men (as asserted by Gall), these very works ought to lead daily to the detection of achromatopsy if it existed ; and we may reasonably conclude that as cases are not discovered they do not exist.