Page:Memoir upon the formation of a deaf variety of the human race (microform) (IA cihm 08831).pdf/31

26 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. (a) The large proportion of deaf offspring resulting from marriages where the father was known to have deaf-mute relatives, and from those where the mother was known to have deaf-mute relatives, and the comparatively small proportion where either parent appeared to be free from hereditary taint, seem to point to the conclusion that in a large proportion of cases in which the marriages were productive of deaf offspring both parents had deaf-mute relatives (even in the ease where one parent was a hearing person).

(b) A similar process of reasoning leads to the conclusion that in a large proportion of marriages where deaf offspring resulted both parents were probably congenitally deaf where both were deaf mutes, and one parent congenitally deaf where only one was a deaf-mute.

(c) It is thus highly probable that a large proportion of the deaf offspring of deaf-mute marriages had parents who were both congenitally deaf and who also both had deaf-mute relatives.

(d) Non-congenital deafness, if sporadic, seems little likely to be inherited.

(e) Another deduction we may make is that more of the deaf offspring whose parents had deaf relatives will marry than of those whose parents were recorded as sporadic cases, for there are them; and they will have a greater tendency than the others to transmit their defect to grandchildren.

These results are in close accordance with the experience of the venerable principal of the Pennsylvania Institution, as expressed in the following letter:

, Philadelphia, November 14, 1883. , Esq.:


 * Continued ill health has prevented an earlier compliance with your request of October 15. The list I now send is full and accurate, according to the records of the institution and my recollection. In regard to most of the cases, I know of no place where fuller information can be obtained than our books furnish.

A residence of more than forty years in this institution has afforded me abundant opportunity for observation in regard to the subject of your research. A statement of the conclusions I have arrived at may be of some interest and use to you.

In regard to the marriage of deaf mutes with each other, if both the man and the woman are deaf from birth, there is very great danger — I should say a strong probability — that some of the offspring will be born deaf. I know a family, however, where the mother is one of three congenitally deaf children and the father one of five, and seven children they have had are all without defect. In the list sent you all the parents, except in two cases, were born deaf. In one of these two cases the father could hear; In the other the mother is a semi-mute.

Where both parents became deaf adventitiously, there seems to be no more probability of the offspring being born deaf than there is where both parents hear.

Where only one of the parents is congenitally deaf, the children almost always hear.

Any further information I can give will be furnished willingly.

Yours, respectfully,

JOSHUA FOSTER.

My attempts to deduce from the records of the marriages of the deaf the influences that cause the production of deaf offspring have met with only partial success. Valuable indications have been obtained, but precise and accurate results are unattainable, on account of imperfect data. It occurred to me some time ago that a different method might lead to an exhaustive examination of the subject. It is known that few of the deaf and dumb married before the establishment of educational institutions in this country, and nearly 78 per cent. of all the marriages recorded in the reports of the American Asylum (the oldest institution in the country), seem to have been contracted since the year 1843. The probabilities are, therefore, that the vast majority of the deaf offspring born are still living, and from them may be obtained an accurate account of their ancestry. It also appeared probable that the majority of these deaf-mutes would at some period