202 MEiMOUtS OF TUE NATIONAL ACADP^MY OF SCIENCES. 



(a) The large propoiti )n of deaf otfspriiift- resulting from marriages where the father was 

 known to liave deaf-mute relatives, and from those where the mother was kuowu to have deaf- 

 mute relatives, and the comi«iratively small proportion wLere either parent appeared to be free 

 from hereditary taint, seem to point to tbe conclusion that in a large proportion of cases in u-liich 

 the marriages iverc productive of deaf offspring both parents had deifmute relatices {even in the case 

 u-hcre one parent teas a hearing person). 



{b) A similar process of reasoning leads to the conclusion tliat in a large proportion of 

 marriages where deaf off'spring resulted both parents icerc probably congcnitally deaf irhere both trere 

 (leaf mutes, and one parent congenitally deaf ic here only one n-as a deaf-mute. 



((•) It is thus liighly probalde that a large proportioyi of the deaf offspring of deaf mute mar- 

 riages 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 deaj 

 relatives will marry th((n of those trhose parents were recorded as sporadic cases, for there are more of 

 them; and they will hare a greater tendency than the others to transmit their defect to the grandchil- 

 dren. 



These results are in close accordance with the experience of tbe venerable princii)al of the 

 Pennsylvania Institution, as exj)ressed in tbe following letter: 



Pennsylvania IxsTrri'Tiox fo]; Ukaf and Du.mu, 



riiiludelpliia, Xoreinher 14, 1.S83. 

 A. Gkaha.m Bell, Esq.: 



Dkai; Sir: Conliur.cil ill licaltli has prcventi'd an earlier compliauce with your request of October 15. Tlie list 

 I uow seurt is full and accurate, according to the records of tbe iustituliou aiul iny rccollectiou. In regard to most 

 of tbe cases, I know of no place wbere fuller iufonnation can be obtained tbau our book.s furnisb. 



A residence of more Iban forly years in tbis institution Las afforded ine abundant oi^portuuity for observation 

 iu regard to tbe subject of your rcscareb. A .statement of tbe conclusions I liave arrived at may be ol' some interest 

 and use to you. 



In regard to the marriage of deaf mutes witb eacb other, if both tbe man and tbe woman are deaf from birtb, 

 there is very great danger — I should say a strong probability — that some of the offspring will be b )rn deaf. 1 know 

 a family, however, where the mother is one of three congenitally deaf children and the father one of five, and tbe 

 seven children they have had are all without defect. In the list sent you all the liarents, 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 ho no more probability of the ot^priug being lorn 

 deaf than there is where both parents hear. ^ 



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



Any further information I can give will be furnished willingly. 



Yours, respectfullv, 



JOSHUA FOSTER. 



My attempts to deduce from the records of tbe marriages of the deaf tbe iufluencss that 

 cause tbe production of ueaf offspring bave met witb only partial success. Valuable indications 

 bave been obtained, but precise and accurate results are unattainable, on account of imperfect 

 data. It occurred to me some time ago tiiat a different method migbt lead to an exhaustive exam- 

 ination of the subject. It is known tbat few of (be deaf and dumb married before tlie establish- 

 ment of educational institutions in this country, and nearly 78 per cent, of all the marriages re- 

 corded in the reports of tbe American Asylum (tbe oldest institution in tbe country), seem to have 

 been contracted since tbe year 1843. The probabilities are, therefore, that the vast majority of tbe 

 deaf offspring born are still living, and from tbein may be obtained an accurate account of their 

 ancestry. It also appeared probable tbat tbe majority of these deaf-mutes would at some jieriod 



