THE STUDY OF INHERITANCE. 621 



fifty-one children, where husband is adventitiously deaf and wife 

 deaf from unknown causes; two marriages, with six children, 

 where both were deaf from unknown causes ; one marriage, with 

 four children, where husband is deaf from unknown causes and 

 wife hears; and two marriages, with five children, where wife 

 is congenitally deaf and husband deaf from unknown causes. 

 None of the 101 children of these forty marriages are reported 

 as deaf. 



In the second group, where from five to six per cent of the 

 children are deaf, eighty-seven are the children of thirty-seven 

 marriages where the husband was congenitally and the wife ad- 

 ventitiously deaf; and 139 are the children of fifty-five marriages 

 where both husband and wife were adventitiously deaf. 



In the third class, where from twelve to eighteen per cent of 

 the children are congenitally deaf, 124 are children of fifty-one 

 marriages where husband was adventitiously and wife congeni- 

 tally deaf ; sixty-six were children of sixteen marriages of hear- 

 ing husband and congenitally deaf wife ; seventy-two were chil- 

 dren of twenty-six marriages where wife hears and husband is 

 congenitally deaf; and seventy-one of twenty-nine marriages of 

 congenitally deaf husband with deaf wife of unknown origin. In 

 all the families of this group one parent was congenitally deaf. 



In the fourth class, where 31*78 per cent of the children are 

 congenitally deaf, all the parents in the fifty-two marriages with 

 one hundred and fifty-one children are congenitally deaf. 



While too few to give quantitative results, these statistics 

 prove that it is the congenital and not the adventitious deafness 

 which is transmitted. 



Of the fifty- two families in which both parents are congeni- 

 tally deaf, twenty-three have congenitally deaf children. 



Of the thirty-seven families in which the husbands are con- 

 genitally deaf and the wives adventitiously deaf, two have deaf 

 children four in one family and one in the other. 



Of the fifty-one families in which the fathers were adventi- 

 tiously deaf and the mothers congenitally deaf, seven produced 

 deaf children, and nine of the congenitally deaf children came 

 from two families. 



There are fifty-five families in which both parents are adven- 

 titiously deaf, and from these have sprung four congenitally deaf 

 children one in each of four families. 



Four of the sixteen families in which the husbands hear and 

 the wives are congenitally deaf have deaf children. 



In five families out of the twenty-six in which the husbands 

 are congenitally deaf and the wives hear, there are children 

 born deaf. 



Six of the twenty-seven families in which the husbands were 



