March 20, 1891.] 



SCIENCE. 



161 



one or both of the parties were born deaf there will be fifteen 

 deaf children in every hundred families; (2) Dr. Gillett's 

 statistics give eighteen deaf children to every hundred fam- 

 ilies; (3) Dr. Turner's, thirty -two; (4) Mr. Williams's, forty- 

 seven; and (5) Mr. Connor's, ninety-five. 



Table II. — Concerning the Offspring of Couples One 

 or Both of Whom were born Deaf. 



Turner (1868). . 



Bell (1883) 



Cormor (1888) . . 

 GiUett (1891) . . . 

 Wmiama (1891) 



Persons who are reported deaf from birth, as a class, ex- 

 hibit a tendency to transmit the defect; and yet when we 

 comis to individual cases we cannot decide with absolute 

 certainty that any one was born deaf. Some who are re- 

 ported deaf from birth probably lost hearing in infancy; 

 others reported deaf in infancy were probably born deaf. 

 For educational purposes the distinction may be immaterial, 

 but in the study of inheritance it makes all the difference in 

 the world whether the deafness occurred before or afterbirth, i 

 . Now, in my researches I think I have found a surer and 

 more safe guide to those cases that are liable to transmit the 

 defect. 



Tlie new guide that I would give you is this: look at the 

 family rather than at the individual. You will find in cer- 

 tain families that one child is deaf and all the rest hearing, 

 the ancestors and other relatives also being free from deaf- 

 ness. This is what is known as a "sporadic" case of deaf- 

 ness, — deafness which afflicts one only in a family. 



Well, the deafness in such cases may be accidental. 

 There is no proof that such deafness is liable to be inherited, 

 excepting whei-e the person is reported deaf from birth. In 

 the vast majority of cases reported deaf from birth there is 

 an undoubted tendency to inheritance; but where the deaf- 

 ness is caused by meningitis, scarlet- fever, or like causes, 

 and no other case of deafness exists in the family, there is 

 probably little, if any, tendency to inheritance. But when 

 you have two members of one family deaf, or three, or four, 

 or five, there you have the proof that a tendency to deafness 

 exists in the family. What I term " family deafness '' ex- 

 ists there. Something has been transmitted from the parents 

 to tlie children that has caused deafness, or helped to cause 

 it, I remember a case in which there were four children in 

 one family deaf, and none of them were born deaf. One 

 child became deaf, perhaps, from measles, another fi'om 

 scarlet-fever, etc. I do not now remember exactly what 

 causes were stated. They became deaf, however, at different 

 times, and from apparently accidental causes. But can we 

 consider that it was accidental that there should have been 

 four children in one family deaf ? The fact that a number 

 of children in the same family are deaf points to an inherited 

 tendency to deafness in the family. One result of my re- 

 searches is to show the great importance of studying the 

 results of marriages of persons who come from families of 

 ' Eef areneea as for Table I. For my own results, see Memoir, p. 25. 



that kind. My results, however, until verified by other ob- 

 servers, should be received as probable only, and not cer- 

 tainly proved. 



So far as I can find out, the hereditary character of the 

 defect in a family is roughly indicated by the proportion of 

 the family who are deaf. If you make a fraction, and place 

 the number of deaf children above as the numerator, and the 

 total number of children below as the denominator, for 

 example, \, that fraction will give you some idea of the 

 tendency to deafness in that family: one child in six is deaf. 

 Again, take a case in which three out of six are deaf (f). 

 Now, the tendency to transmit deafness in this family (f) 

 will be greater than in that (-g). Every member of the first 

 family (|), whether deaf or hearing, will have a greater 

 tendency to have deaf childrer* than the members of the 

 other (^). In general, the tendency to transmit deafness is 

 greatest in those families that have the largest proportion of 

 deaf members, and smallest in those that have the least. 

 This conclusion is exceedingly probable, and should therefore 

 be taken as a guide by those who desire to avoid the produc- 

 tion of deaf offspring. If you marry a hearing person who 

 has three or four deaf brothers and sisters, the probability of 

 your having deaf children will be greater than if you marry 

 a deaf person (not born deaf) who has no deaf relatives. 



The statistics collated by me ("Memoir," p. 35) indicate 

 that 816 marriages of deaf-mutes produce 82 deaf children: 

 in other words, every 100 marriages are productive of 10 

 deaf children. That is a result independent of the cause of 

 deafness, — an average of all cases considered. Eliminating 

 40 cases where the cause of deafness is not given, I divide 

 the remaining 776 cases into 4 classes : — 



Class 1. Persons not born deaf who have no deaf rela- 

 tives. 



Class 2. Persons not born deaf who have deaf relatives. 



Class 3. Persons born deaf who have no deaf relatives. 



Class 4. Persons born deaf who have deaf relatives. 



Table III. 



The percentage results are shown by themselves in the 

 following table (Table IV.), in which the figures indicate 

 the number of deaf children produced by every 100 marriages 

 of persons belonging to Classes 1, 2, 3, and 4. 



Table IV. 



My statistics are confessedly very imperfect, and many 

 persons have hastily concluded that the results are therefore 



