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sence of deaf relatives. In cases where the parents are not congenitally deaf and have no deaf relatives, the proportion of deaf children is very low. When one or both parents are congenitally deaf or have deaf relatives--when the deafness is inherited or in the family--the likelihood becomes far greater, and greater still when the two influences are in conjunction. In general, in respect to the influences of heredity upon deafness, the main determinants seem to be found in the existence in the parties, whether hearing or deaf, of deaf relatives, and, to a less extent, in the existence in parties who are deaf of congenital deafness. POSSIBLE ACTION FOR THE PREVENTION OF CONGENITAL DEAFNESS We come now to the consideration of the question of possible action for the prevention of congenital deafness. This examination naturally centers about the matter of the regulation of marriage, with due attention to the extent that action on the part of the state is to be regarded as desirable or feasible. We have seen that congenital deafness may, hypothetically, be divided into three distinguishable classes: that in which consanguineous marriages are concerned, that in which there is antecedent deafness in the family, and that in which neither of these conditions occurs; and in our inquiry it has seemed best to take up each of these separately. It may be, however, that there is in fact no very radical difference between these several forms, and that with increased knowledge on the subject a more or less intimate relation will be found to exist. Of that form of deafness in which neither consanguineous marriages nor antecedent deafness is involved, we are at present, as we have noted, able to say little definitely. In most cases we may be convinced that there exists in the parent some peculiar state of morbidity or other affection, latent or manifest, perhaps to some extent of hereditary influence, which has an effect on the organs of hearing of the offspring. A certain proportion is quite possibly due to recognizable defects both of physical and mental character. Our statistical evidence, however, in respect to this form of congenital deafness is too slight to warrant any positive deductions; and we will have to wait for further investigation to determine its nature fully. None the less, marriage of persons known to be liable to have ill effect on possible offspring is objectionable for not a few reasons, from the standpoint
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