XII] 



Diseases of the Eye 



221 



departure from this rule has occurred in the ten generations 

 that have elapsed since the birth of the earliest known case 

 (born 1637). The people are peasants living in a group of 

 somewhat isolated villages in the south of France. Adding 

 together all the families which can be regarded as the off- 

 spring of affected and presumably heterozygous {DR) 

 individuals mated with normals the numbers are 130 affected 

 and 242 unaffected"^. These figures depart very widely from 

 the expected equality. Nettleship thmks there are reasons 

 for supposing the number of affecteds somewhat understated, 

 through a disposition to conceal the infirmity This cannot 

 however account for the whole discrepancy, since error 

 introduced from this cause would lead to the production of 

 affecteds from alleged normals which has never occurred. 

 It is of course possible that several who died before their 

 condition was ascertained may have been counted as normals 

 in past generations, 



Qualitatively the descent is evidently that of a dominant, 

 and though perhaps these aberrant numbers point to a 

 genuine complication such a conclusion can scarcely be 

 drawn positively from materials of this kind. 



It is somewhat remarkable that stationary night-blindness 

 usually follows a sex-limited descent, and the absence of any 

 sex-limitation in the genealogy just spoken of, suggests that 

 the physiological nature of the affection in this family may 

 be distinct. There is, I understand, nothing which yet 

 differentiates the one condition from the other unless it 

 be that the sex-limited kind is usually associated with 

 myopia which was not conspicuous here. 



In the recorded pedigrees there are indications that, in 

 addition to those already mentioned, the following ophthalmic 

 diseases or malformations may be transmitted as dominants 

 sometimes, though the evidence does not justify a compre- 

 hensive general statement and many exceptional cases are 

 known. 



Distichiasis : development of eye-lashes in place of 

 glands on inside of eye-lids (perhaps a homoeotic variation). 



* In one case an affected pair married and their two daughters were 

 affected. Of these one (who may have been DD) had two affected 

 children. The totals given above are arrived at after deduction for this 

 family. 



