12/j. 



JOURNAL OF SCIENCE. 



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 

 from 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 researches is to show the great importance of studying 

 the results of marriages of persons who come from families of that 

 kind. My results, however, until verified by other observers, should 

 be received as probable only, and not certainly 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 (j|). Now, the 

 tendency to transmit the deafness in this family (-;}) will be greater 

 than in that (,\). Every member of the first family (■§), whether deaf 

 or hearing, will have a greater tendency to have deaf children 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 production 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. 25) indicate that 816 

 marriages of deaf-mutes produce 82 deaf children : in other words, 

 every 100 marriages are productive of 10 deaf children. This 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 776 cases into 4 classes : — 



Table III. 



Class 1. Not bom deaf, no deaf relatives 



Class 2. Not born deaf, deaf relatives 



Class 3. Bom deaf, no deaf relatives 



Class 4. Born deaf, deaf relatives 



CD 13 



363 



53 



130 



230 



a a ffi 2 



fc 6 



18 



5 



15 



41 



g fa a S S g 



4-7 



9-4 



11-5 



17-8 



The percentage results are shown by themselves in the following 

 table (Table IV.), in which the figures indicate the number of deaf 



