Consanguinity.—The question of the importance of consanguinity as a cause of deaf-mutism has been a fruitful sub ject of discussion. The first decidedly expressed opinion upon this topic ap peared in 1S-16, when Meniere and Puy bonnier's, who were, respectively, med ical attendant and teacher at the State Deaf and Dumb Institution in Paris, laid great stress upon the important part which consanguinity played in deaf-mutism, without, however, produc ing statistics in support of their theory. Such, however, appeared shortly after in the returns of the Irish census of 1851, which was the first to include this ques tion in its rubrics, and, from the results thus obtained, Wilde came to the con clusion that "among the predisposing causes of mutism the too-close consan guinity of parents may be looked upon as paramount." Vulliet, Landes, Chaza rain, Bemiss, Howe, Dahl, Boudin, Mitchell, and the undaunted defender of the doctrine of consanguinity, Devay, were all in favor of the importance of this factor in the etiology of deaf-mutism, while Bourgeois, Perier, Huth, Voisin, and G. Darwin were more or less op posed to the hypothesis that consan guineous marriages predispose to degen eration in the offspring, deaf-mutism be ing generally the principal object of their arguments. Statistical information as to the frequency of consanguinity among the parents of deaf-mutes has also been forthcoming, the frequency with which deaf-mutes are reported as being born in consanguineous marriages varying from 1.6 to 9.4 per cent., while the percentage for deaf-mutes with congenital deafness -varies from 2.8 to 23.0 per cent.
It will be seen, then, that statements as to the frequency with which deaf mutes are born in consanguineous mar riages differ considerably. This can most naturally be explained as resulting from various circumstances. To begin with, such marriag-es vary in frequency in different countries; thus, in Prussia they form only 0.S per cent. of all mar riages; in France 1 to 2 per cent.; and in England 3 per cent. at the outside; in Denraark 3 to 4 per cent., in Saxony 4, and in Norway over 6.65 per cent. Fur ther, there is no doubt that the frequency of consanguineous marriages differs in the different confessions and classes of society, in cities, and in the country, and here, also, in different districts. It must also be observed that the various statis- , tics sometimes embrace whole countries, sometimes single districts, and sometimes deaf-and-dumb institutions, clinics, etc. The information in question has also been obtained in different ways; for in stance, by reports, censuses, individual investigations, etc., and finally the dif ferent authors have included different degrees of relationship.
Although many investigators have found comparatively few deaf-mutes born in consanguineous marriages, there are several circumstances which seem to prove that consanguinity is an impor tant factor in the etiology of deaf-mut ism. They are the following:— Several statistical reports, the relia bility of which cannot be doubted, are to the effect that deaf-mutes are com paratively often born of consanguineous marriages, and there seems to be reason to lay greater stress upon such positive results than upon those pointing in a negative direction.
All authors are unanimous in declar ing consanguineous origin to be more common among congenital deaf-mutes than among deaf-mutes in general. This indicates that it is deaf-mutes witk ac quired deafness who reduce the rate that expresses the frequency with which deaf mutes in general are born in consan guineous marriages. That consanguinity plays a part in congenital deafness only, or almost only, may be seen from the circumstance that all authors who have occupied themselves with this subject have come to the result that deaf-mute children born of consanguineous mar riages are, in the majority of cases, born deaf, while only a small majority become deaf after birth.
That consanguinity is of importance in the etiology of deaf-mutism is evident from the circumstance that several au thors have proved that, among the mar riages of which the deaf-mutes are born, the consanguineous unions produce a larger number of deaf-mutes than the crossed.
Finally, several statisticians have proved that, the closer the degree of re lationship between the parents, the larger was the number of deaf-mute children born.
It will be seen that there are various circumstances which clearly indicate that the intermarriage of relatives plays no insignificant part in the etiology of deaf mutism. Everything, however, tends to prove that it is entirely, or principally, in congenital deafness that consanguinity is an important etiological factor.
It is, however, undecided whether con sanguinity in itself is a remote cause of deaf-mutism, or whether it is through the intensified transmission of heredi tary, morbid conditions or tendencies prevalent in a family that it makes itself felt. Theoretical considerations and a few lately published investigations in Norway by Uchermann are strongly in favor of the latter supposition; still it is but fair to say that up to the present there have not been many or convinc ing facts brought forward in its support.
There are, then, but few facts which serve to elucidate the question whether , the influence of consanguinity upon deaf mutism is direct or indirect. Further in vestigations of the same nature will, per haps, throw more light upon this sub ject. The final solution of the question will, however, in all probability, only be brought about by means of information as to the family, supported by an exact knowledge of the relatives of the deaf mutes, and supplemented by their thor ough objective examination. It is only thus that it will be possible to find less pronounced, but not on that account less important, abnormalities in the family, and to discover with what frequency the influence of heredity can be, with cer tainty, excluded in consanguineous mar riages resulting in deaf-mute children.