Up to the present time, the mental condition of the blind has not been studied in a sufficiently precise manner to permit of our clearly appreciating the modi fications which occur in the character or fashion of their ideas, under the influence of the arrest of development of their optic impressions. Nevertheless, we may say with Dumont, who has already occupied himself with this question, that the influence that optic impressions exercise upon the play of the cerebral functions is most important, and that a certain number of indi viduals, whom he had an opportunity of observing, presented, from a psychical point of view, changes of temper and symptoms of melancholy, all the more marked because the patients were incapable of dis cerning day from night.* As regards such phenomena, Bouisson has observed a most remarkable case.t The patient was a young man who had became insane in consequence of a double cataract, with incoherence of ideas, complete failure of spontaneity. Bouisson, from the antecedents of the patient, hit on the happy idea of performing an opera tion. It was simultaneously performed in both eyes, by couching, and a few days afterwards, when optic im pressions reappeared to stimulate regularly the scnsorium of the patient, and vision was restored to him, he began to utter a few sensible words, his mental state became progressively better, and, at the end of a few weeks, he left the hospital capable of attending to his own wants.
Baillarger has also reported analogous facts. Thus, he cites from Whytt the case of a patient who, if his eyes were closed by another person, even without sleeping, fell into a great disorder of mind. It seemed to him that he was transported through the air, and that his limbs were falling off.
In a patient of twenty-seven, whom he observed him self, he noticed that as soon as she shut her eyes, she saw animals, fields, and houses. " I several times closed her lids myself," he says, "and immediately she men tioned to me a number of objects that appeared to her.".t.
Evolution of Acoustic Impressions.—Acoustic impres sions, like optic impressions, play a most important part in the sum-total of the manifestations of mental activity. Like them, they are incessant during the whole diurnal period, and by their uninterrupted stimu lation maintain cerebral functionment in a perpetual condition of erethism. They are, for us, the natural vehicles of the notion of sound and harmony, while, at the same time, they are the generating elements of articulate language. Through them the ears are charmed, the understanding perceives and interprets, according to conventional methods, articulate vocal sounds, and the human personality thrown into emotion vibrates externally, and expresses itself in regularly co-ordinated vocal sounds.
They are collected at the periphery of the acoustic sensorial plexuses, and, like their fellows, are condensed in special ganglia of the grey substance of the posterior regions of the optic thalamus, and thence radiated, prin cipally into the posterior regions of the cortical sub stance, which, in the human species, present such a characteristic development. According to Wundt, they
are the impressions most rapidly transmitted to the perceptive centre.
Like their fellows, they have a double range ; they enter into relation successively with the psychic sphere and the intellectual sphere proper, and in these two regions of nervous activity they excite specific reactions of the same nature as their fellows do.
T. When dispersed in the plexuses of the sensorinnz they at first develop there the same reactions of plea sure and pain that we have seen succeed each other in consequence of the arrival of sensitive and optic im pressions, according to the same physiological processes. The variable condition of impressionability of the peri pheral regions is always transmitted into the central regions, and there excites concordant emotional states. When the ears are charmed, the sensorium is similarly delighted, and inversely when the ears are impressed with a certain rhythm and with certain modulations into flat or sharp keys, the same states are impressed upon the sensorium.
Thus it is that grave musical sounds, repeated very slowly and in a chanting manner—musical phrases in flat keys, and andante—dispose the sensorium to reminis cence, and produce in us a special condition which constitutes sorrow ; and that, inversely, loud music, consisting of rapid notes, and allegro in tempo, or airs in ;,-time and tricked out with sharps, awakes emotions of an entirely different nature, predisposing the heart to gaiety and mirth, and inviting us to dance spontaneously and move our limbs to its cadence.
Between these two limits of profound sorrow and expansive joy, between which acoustic impressions cause our natural sensibility to oscillate, there is a whole series of intermediate notes which may be successively set in vibration.
Music, indeed, v.ith its infinite number of tones, is capable of impressing us in various manners, and deve loping sensitive conditions very distinctly graduated. It is, like spoken language, of which it is but an amplifica tion, designed to form a sort of synthetic language, and to join the train of the cardinal sentiments which are capable of causing the plexuses of the human sensorium to vibrate. Thus musical sounds now express tender sentiments, flowing forth in sweet harmonious notes, and in slow time ; while in other circumstances, with that richness of expression the great masters have given to their works, we see a melodious phrase augmented by graduated accompaniments become infinitely complicated, and with the aid of powerful orchestration symbolise the most complex sentiments, not merely of man considered as a sentient unit, but even of man considered as a social unit. Thus it is that the great masters have succeeded in expressing in music the different shades of human sensibility, just as the masters of painting have done with their palette,* and in indelibly imprinting their inmost thoughts, and the sentiments with which they were animated, upon the sensorium of those who comprehend them.