BOWMAN LECTURE. CXIII 



in 11 pedigrees 23 affected males became fathers and 

 had 100 children who lived long enough to have the 

 disease, the males and females being in about equal 

 numbers; only 6 of the JOO became affected, 4 males and 

 2 females. II. An affected female has generally,, like an 

 affected male, had both parents normal ; it is rare to 

 find that she had an affected father or an affected 

 mother. III. An affected female may transmit the 

 disease to her children of either sex, but of her sons 

 some usually escape. It is not clear why there should 

 be this difference between colour-blindness and Leber's 

 disease in the transmission to and by an affected female. 

 We may note, however, that the one condition is an 

 actually innate physiological defect, the other a disease 

 of which in the vast majority of cases we cannot say 

 more than that the liability to it is innate. 



But although a woman suffering from Leber's disease 

 does not, as a rule, give the disease to all her sons, she 

 does give it to a larger proportion of her total issue than 

 she would do if she only carried it incomplete or latent 

 in the ordinary way : I. In 12 completed sibships, where 

 the mothers were affected but the fathers normal and the 

 siblings of the necessary age normal, 64 children survived 

 and 33 had the disease, viz., 21 males and 12 females. 

 II. In 38 similar sibships where the mothers were 

 normal, but carried the disease (the fathers also being 

 normal), there were 215 eligible children of whom 65 got 

 the disease, 64 males and 1 female. In the first case one 

 half, and in the second case rather less than one third of 

 the children suffer, and the difference is almost entirely 

 due to the excess of affected daughter a in the first group, 

 viz., the group where the mother had the disease. 



In one extraordinary case (Case 49, supra) all 7 

 children (4 male, 3 female) of the normal and unrelated 

 parents (III, 5 and 6) had the disease, and had it unusually 

 early in life. 



The number of children born in the childships con- 

 taining cases of Leber's disease is seldom less than the 



