THE INHERITANCE OF FAMILY TRAITS 131 



■tO 



and it cannot be doubted that such a weakness plays a role 



in deafness. Thus Bell (1906) has shown that, in the census 



returns, over 55 per cent of the deaf 



children in the country come from 



parents who became deaf in adult 



life and he states that this ^'confirms 



the conclusion reached upon other 



grounds that heredity sometimes 



plays a part in the production of 



catarrh of the middle ear — the chief 



cause of deafness occurring in middle 



life." 



Fig. 103.— Pedigree of 

 on ci -Tk otosclerosis. Affected per- 



29. bKIN Diseases gons (black symbols) for 



the most part, but by no 



The skin is an admirable organ for means always, have an af- 

 the protection of the delicate in- ^^^^^^ parent. Luc^, 1907. 



ternal parts not only from desiccation but also from the 

 entrance of the numerous parasites that thrive on mammal- 





I 



m 



E 



4^ 



Fig. 104 — Pedigree of otosclerosis. The condition of hearing in the first 

 generation is unknown and some of the children in the fourth generation have 

 not reached the age of incidence; thus, IV, 4r-6. are 22 to 18 years old and 

 IV, 7-9, are 20 to 14 years. 



ian blood and tissues. Nevertheless, its exposed position 

 renders it liable to attack by the various germs that are 



