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; four in a family, 19.0 per cent; more than four in a family, 21.1 per cent.

                      TABLE XXV.
Number of Congenital Deaf mutes to a Family in Ireland. -----------------------------------------------
-----------------
     | | Families in which deaf-mutes numbered.
     | |----------------------------------------
Year.| Parentage. | 1. | 2. | 3. |4.|5.|6.|7.|8.|9.|10.|11. ------------------------------------------------------------
---- 1851 | Parents cousins | 127| 45 | 20 |10| 5| 2|..| 1|..|.. |.. 1871 | Parents cousins | 91| 38 | 24 | 5| 3| 1| 1|..|..|.. |.. 1881 | Parents cousins | 63| 30 | 13 | 6| 1|..|..|..|..|.. |.. 1891 | Parents cousins | 82| 38 | 19 | 9| 1| 3| 1| 2|..|.. |.. 1901 | Parents cousins | 79| 34 | 23 | 7| 1|..| 1|..|..|.. |.. 1851 | All families[A] |2963|347 |158 |35|13| 5|..| 1|..|.. |.. 1871 | All families[A] |2460|305 |167 |47|20| 5| 1|..|..|.. |.. 1881 | All families[A] |2080|281 |162 |39|18| 6|..|..|..| 1 |.. 1891 | All families[A] |1473|273 |134 |40|12| 6| 1| 2|..|.. | 1 1901 | All families[A] |1219|231 |122 |34|10| 4| 2|..|..|.. |.. ---------------------------------------------
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  [A] Number of the “Deaf and Dumb” to a family, “as far as
      could be ascertained.”