BOWMAN LECTURE. 



normal, and is sometimes very large. In 44 completed 

 childships, each containing one or more affected, with 

 both parents normal, 28 contained 7 children or more, 10 

 of these having from 10 to 14 each, and one had 16. In 

 19 similar affected childships where one parent had the 

 disease, 8 had 7 or more children, 2 of these having 10 

 and 2 having 14, 11 contained 6 or less. It is notice- 

 able that in both these sets of sibships (44 and 19), those 

 in which females as well as males were diseased averaged 

 rather larger than those with only males diseased, as 

 8'25 to 7. The normal branches of affected stocks are 

 seldom fully recorded, but in such of them as seem 

 complete we find several containing 9 and 10 children 

 each. So it is clear, on the whole, that the stocks in 

 which Leber's disease is found are quite up to the normal 

 in fertility, that the sibships in which the disease occurs 

 are larger than normal, and frequently very large; and 

 further, that the affected ones who marry often beget full 

 families. 



JUit if the births are too many the early mortality is 

 large, sometimes very large, especially among the male 

 children. This has been pointed out by several writers, 

 notably by Gould. We find that in the sibships that 

 have been reduced by a high early death-rate, the pro- 

 portion of the survivors who get the disease is larger 

 than in those sibships where few or none have died ; 

 almost half of the former became affected, including 

 several females, but where no early deaths took place the 

 proportion affected is one third. 



One naturally suspects that a disproportionate number 

 of those who died early would have suffered from the 

 disease had they lived long enough, and that thus early 

 deaths may contribute to the extinction of the disease ; 

 but this, of course, is at present a mere guess. 



In several families there has been a high mortality from 

 phthisis, but the number of such families is too small to 

 justify any inference. 



The characters of the disease are usually the same in 



