Chap. XII. 



INHERITANCE. 



9 



sequence of something like inflammation of the coats, under which they 

 yield, and there is ground for believing that it may often originate in 

 causes acting directly on the individual affected, and may thenceforward 

 become transmissible. When both parents are myopic Mr. Bowman has 

 observed the hereditary tendency in this direction to be heightened, and 

 some of the children to be myopic at an earlier age or in a higher degree 

 than their parents. Thirdly, squinting is a familiar example of hereditary 

 transmission : it is frequently a result of such optical defects as have been 

 above mentioned; but the more primary and uncomplicated forms of it 

 are also sometimes in a marked degree transmitted in a family. Fourthly, 

 Cataract, or opacity of the crystalline lens, is commonly observed in 

 persons whose parents have been similarly affected, and often at an earlier 

 age in the children than in the parents. Occasionally more than one child 

 in a family is thus afflicted, one of whose parents or other relation presents 

 the senile form of the complaint. When cataract affects several members of 

 a family in the same generation, it is often seen to commence at about the 

 same age in each ; e.g., in one family several infants or young persons may 

 suffer from it ; in another, several persons of middle age. Mr. Bowman also 

 informs me that he has occasionally seen, in several members of the same 

 family, various defects in either the right or left eye ; and Mr. White Cooper 

 has often seen peculiarities of vision confined to one eye reappearing in 

 the same eye in the offspring. 17 



The following cases are taken from an able paper by Mr. W. Sedgwick, 

 and from Dr. Prosper Lucas. 18 Amaurosis, either congenital or coming on 

 late in life, and causing total blindness, is often inherited ; it has been 

 observed in three successive generations. Congenital absence of the iris has 

 likewise been transmitted for three generations, a cleft-iris for four gene- 

 rations, being limited in this latter case to the males of the family. Opacity 

 of the cornea and congenital smallness of the eyes have been inherited. 

 Portal records a curious case, in which a father and two sons were rendered 

 blind, whenever the head was bent downwards, apparently owing to the 

 crystalline lens, with its capsule, slipping through an unusually large pupil 

 into the anterior chamber of the eye. Day-blindness, or imperfect vision 

 under a bright light, is inherited, as is night-blindness, or an incapacity to 

 see except under a strong light : a case has been recorded, by M. Cunier, of 

 this latter defect having affected eighty-five members of the same family 

 during six generations. The singular incapacity of distinguishing colours, 

 which has been called Daltonism, is notoriously hereditary, and has been 

 traced through five generations, in which it was confined to the female 

 sex. 



With respect to the colour of the iris : deficiency of colouring matter is 

 well known to be hereditary in albinoes. The iris of one eye being of 

 a different colour from that of the other, and the iris being spotted, are 

 cases which have been inherited. Mr. Sedgwick gives, in addition, on the 



tf Quoted by Mr. Herbert Spencer, 

 ' Principles of Biology,' vol. i. p. 244. 

 18 'British and Foreign Medico- 



Chirurg. Review,' April, 1861, pp. 482- 

 6; THere'd. Nat.,' torn. i. pp. 391-408. 



