DEFICIENT DEVELOPMENT OF THE MENTAL FAcuurrEs.—There can be no doubt that the want of such an important sense as hearing must at least result in a slow development of the mental facul ties, as the psychological function of the brain develops not only in proportion to its receptivity to impressions from without, which are so necessary for mental growth ("nihil est in, intelleeta pod non antea fuer-it in sensibus"), and to the quality of these impressions, but also in proportion to their quantity, which must of necessity be diminished when one of the routes by which they reach the brain is closed or partly closed. This does not, of course, prevent a deaf mute from attaining the same degree of intellectual development as a normal person with the same amount of intelli gence, if his physical deficiency is com pensated for by energy, industry, etc. There is, however, no doubt that purely practical considerations—for instance, the necessarily-limited choice of profes sions—often hinder such a complete in demnification for the loss of so impor tant a sense as hearing. The deaf-mute is thus deprived of one of the most im portant incentives to energy,—namely, ambition; and it is, doubtless, in these external hindrances, that the reasons are to be sought why no deaf-mute has as yet written his name on the pages of history. Further, the morbid processes causing deaf-mutism often have their seat in the brain, as has been already pointed out, and these processes often leave other traces behind them. Hart
mann found also that one-balf of the pupils examined by him in deaf-and dumb asylums, whose deafness was due to brain disease, were but moderately or indifferently endowed with intelligence, and it was altogether doubtful whether many of these subjects were capable of instruction. There are also statistical proofs from other countries that deaf mutism is often accompanied by want of mental power. It is not, however, cor rect to infer that deaf-mutism can result in idiocy from the circumstance that deaf-mutes are often idiots. Idiocy, when it appears simultaneously with deaf-mutism, is the result of a congenital brain disease, or one acquired in infancy, and is of superior or co-ordinate impor tance to the deaf-mutism itself; persons exhibiting both these abnormalities must, doubtless, not be considered as idi otic deaf-mutes, but as deaf-and-dumb idiots. TT. Schmaltz and T,emclre have made some measurements of the heads of deaf-mutes in order to elucidate the question as to the intelligence possessed by deaf-mutes. Both these investigators found that the heads of deaf-mute chil dren were, as a rule, smaller than the heads of normal children, especially in the younger age-periods. The reason is, doubtless, that the mental faculties of deaf-mute children are less developed than those of other children.