42 Heredity. 



who were insensible to all sounds above and below the diatonic 

 scale. 



To be congenitally deaf and dumb exerts a well-known and 

 unfortunate influence on the development of the intellect, for 

 which the only remedy is found in the use of artificial signs. If 

 this infirmity is transmissible, heredity may be said to penetrate 

 into the very essence of intellect. But this form of heredity has 

 been disputed. 



Dr. Meniere, in a special work on this question, while admitting 

 that in a certain number of instances the direct and immediate 

 heredity of deaf-muteness has been established, says : ' Never- 

 theless, these facts must be held to constitute a rare exception ; 

 habitually deaf-mutes married to deaf-mutes beget children who 

 hear and speak. This is, of course, still more the case where the 

 marriage is a mixed one, that is, where only one of the couple is 

 deaf and dumb though even in this case there are well-attested 

 cases of heredity.' l Darwin also says : c When a male or a 

 female deaf-mute marries a sound person, their children are most 

 rarely affected ; in Ireland, out of 203 children thus produced 

 only one was mute. Even when both parents have been deaf- 

 mutes, as in the case of forty-one marriages in the United States, 

 and of six in Ireland, only two deaf and dumb children were 

 produced.' 2 



We would remark that the returns of the Deaf and Dumb 

 Institution of London, from its foundation to the present time, are 

 conclusive in favour of heredity. Among 148 pupils in that 

 institution at one time, there was one in whose family were five 

 deaf-mutes ; another in whose family were four. In the families 

 of ii of the pupils there were three each, and in the families of 19, 

 two each. 



It is quite possible that, in the case under consideration, the 

 law of heredity is not so much at fault as is commonly supposed. 

 The deaf-muteness of ascendants may, in their descendants, be 

 transformed into an infirmity of some other description, such 

 as hardness of hearing, obtuseness of the mental faculties, or 



1 Recherches sur VOrigine de la Surdi-Mutite, par le Docteur Meniere. 



2 Variation, etc., ii. p. 22. 



