BOWMAN LECTURE. LXXV 



than, normal stocks of the same social class. In regard 

 to more general signs of inferiority we are told by Mr. 

 Heron that, at any rate for the London districts, " there 

 is a very close relationship between undesirable social 

 status and a high birth-rate."* We shall see presently 

 that the same is apparently true for retinitis pigmentosa 

 and other eye diseases. Some caution, however, is 

 needful in concluding that large birth-rate and disease 

 are as closely connected as they appear to be ; for some 

 pedigrees of disease have been selected for investigation 

 just because they contain large numbers of accessible 

 members,, and the prevalence in them of large childships 

 may be only what is normal to the particular population, 

 class or stock. 



I will refer next to the question of sex liability in some 

 of the hereditary eye-conditions. 



We have first the sex-limited group ordinary colour- 

 blindness, Leber's disease of the optic nerves, and one 

 form of congenital stationary night-blindness. In these 

 so large a majority of the affected persons are males that 

 affected females are regarded as rare exceptions ; and 

 this rule holds in general terms for each separate family 

 as welt as for the aggregate. 



Next come diseases that have 110 special correlation 

 with sex ; the lump sum of males and females is about 

 equal, or at most not widely different, although separate 

 families often display marked departures from the rule, 

 one having a great excess of males, another of females. 

 The best examples are all forms of post-natal cataract, 

 glaucoma (so far as we yet know), and a second form 

 of congenital stationary night-blindness. Probably other 

 diseases will be added to this group. 



In the third group containing all forms of congenital 



* " On the Relation of Fertility in Man to Social Status and on the 

 Changes in this Relation that have taken place during the last Fifty 

 Years," David Heron, 19()o, Drapers' Company Research Memoirs : Studies 

 in National Deterioration, p. 21. 



