n£n 



130 HEREDITY IN RELATION TO EUGENICS 



mucous lining of the ear. Some examples of strains showing 

 otosclerosis are given in Figm-es 101-104. 



An examination of the available pedigrees indicates that 

 otosclerosis is due to a defect — perhaps to the absence of a 



resistance to infection and in- 

 flammation of the lining mem- 

 brane of the inner ear. Like 

 I — -. other defects it is relatively com- 



j— . X fJ-i/->^ nion in the progeny of cousin 



" — "l^ I— nvy marriages. 



The eugenic indications then 

 are, two persons with a tend- 

 ency towards otosclerosis should 



Fig. 101. — Pedigree of oto- << • r • i 



sclerosis. In this pedigree all refrain from marrying, as prob- 

 affected individuals, so far as ably all of their children will he 



known, are females. Luc^, 1907. , , - , . -r, , 



hard of hearing. But a person 

 with otosclerosis and an unaffected person of an untainted 

 strain may marry with impunity as their children will prob- 

 ably all have strong hearing. 



Ui 



0|i~io 



DiOD aoo 



iiiiiiiii 



Fig. 102. — Pedigree of a family with otosclerosis. Two deaf brothers 

 marry; one has a single son, who is deaf; the other has four unaffected chil- 

 dren. Of these latter two marry consorts who are, so far as known, normal. 

 From one pair three out of nine children are affected; from the other only 

 one child is known and he is hard of hearing. Hammerschlag, 1906. 



c. Catarrhal affections. — That a weakness of the mucous 

 membranes permitting catarrh is hereditary, we shall see 

 in speaking of the weakness of mucous membranes in general, 



