| to a | |Per | to a
year. |population|Number|million|family[A]|Number|cent.|family[A]
------------------------------------------------------------------
1851[B]| 6,574,278| 4,127| 628 | ---- | 242 | 5.86| 1.66
1861 | 5,798,967| 4,096| 706 | 1.22 | 362 | 8.84| 1.72
1871 | 5,412,377| 3,503| 647 | 1.30 | 287 | 7.35| 1.76
1881 | 5,174,836| 3,163| 611 | 1.32 | 191 | 6.04| 1.69
1891 | 4,706,448| 2,570| 546 | 1.40 | 297 |11.56| 1.92
1901 | 4,456,546| 2,179| 489 | 1.40 | 249 |11.43| 1.73
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[A] From Table XXV.

[B] 1851 data from Huth, "Consanguineous Marriage and
Deaf-mutism." _The Lancet_, 1900.

Table XXIV summarizes the most important points in the Irish data. It
will be seen that while there has been an absolute diminution in the
number of deaf-mutes in Ireland with the decrease in population, there
has been a relative increase of deaf-mutism. There are two possible
explanations for this phenomenon, both of which may have operated in
part; first that in the great emigration the deaf-mutes have been left
behind, and second that with the introduction of improved methods of
census taking, the returns are more complete than a half century ago.
Mr. Huth believes that there is still room for improvement in Irish
census methods, and thinks there is reason to believe that in the
enumeration of the deaf all children born deaf in a family are
included whether living or not.

Since Ireland is strongly Roman Catholic, the proportion of
consanguineous marriages is probably small, so that the percentage of
deafmutes derived from consanguineous marriages, varying from 5.86 to
11.56 is very much greater than the percentage of these marriages in
the general population. The average number of deaf children to a
family in Table XXIV varies less than any other part of the table, and
clearly shows a much higher average number of deaf children where the
parents were cousins. They reveal the interesting fact that the
occurrence of two or more deafmutes in a family is more than twice as
probable where the parents are related as where they are not. Table
XXV still better illustrates this point. Of the families where there
was but one deaf-mute, only 4.3 per cent were the offspring of cousin
marriages; where there were two in a family 12.9 per cent were of
consanguineous parentage; three in a family, 13.3 per cent;