HEREDITY OF NORMAL CHARACTERS. 19 



by inheritance. The peculiar imperfection of vision 

 manifested in the inability to distinguish colors 

 popularly known as color-blindness is also hereditary. 

 Of the many instances on record of the hereditary 

 transmission of this defect, the following is perhaps 

 the most remarkable. Dr. Pliny Earle says: "My 

 maternal grandfather and two of his brothers were 

 characterized 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 in- 

 quiries 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 the perception of colors. In the second, of 

 a family consisting of seven brothers and eight sisters, 

 three of the brothers one of whom, as before men- 

 tioned, was the grandfather of the writer had the 

 defect in question. In the third generation, consist- 

 ing of the children of the grandfather aforesaid, of 

 three brothers and four sisters, there was no one 

 whose ability to distinguish colors was imperfect. In 

 the fourth generation, 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 

 color. 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 



