LXXVIII BOWMAN LECTURE. 



its indirect power of lowering the resistance to hurtful 

 influences. The purely hereditary diseases of the eye do 

 not seem to have any relation to length of life, at any 

 rate a good many old persons are found in pedigrees of 

 cataract, glaucoma, retinitis pigmentosa, Leber's disease, 

 and albinism. But the subject has not yet been at all ade- 

 quately looked into ; and attention may suitably be called 

 to the importance of recording everything we can about 

 age in every member of a morbid pedigree; age of parents 

 at marriage ; age at onset of the disease in those affected ; 

 age at death, especially when the disease has " anticipated/' 

 Every effort should also always be made to get the 

 order of all the births, or rather of all the conceptions, 

 and the intervals between them. Only in that way can 

 we find out whether a disease tends to affect the earlier 

 or the later births to excess. Karl Pearson's studies of 

 the statistics of phthisis, insanity and crime lead him to 

 believe that the earlier born children are more frequently 

 predisposed to those conditions than the later ones.* 

 Laqueur considered that the first and second born were 

 decidedly less likely to suffer from hereditary diseases of 

 the eye than the third and later births ; but his remarks 

 were based on only forty-eight families, containing in all 

 no more than 244 children.t Berry has pointed out that 

 in' a particular pedigree of cataract (Fig. 24) the eldest 

 born girl of each sibship invariably had the disease. 



CATARACT. J 



(Figs. 11 to 27.) 



It is well known that cataract often runs in families, 

 sometimes appearing in several generations. This has 

 been ascertained beyond doubt for several of the best- 



* A First Study of the Statistics of Pulmonary Tuberculosis, 1907, p. 25, 

 Boyle Lecture. Also The Problem of Practical Eugenics, 1909, p. 19, etc. 



t Laqueur, Zeitschrift f. PraUische Aerzte, 1897, No. 21, p. 8. 



+ For the abbreviated titles of periodical publications referred to in 

 this or subsequent sections see Appendix IX. 



