(_b_) Acoustic Apparatus.—We know less of the sensory disturbances in the organs of hearing. Hyperæsia shows itself by undue (painful) sensitiveness to sounds, and by the ability to perceive sounds which are inaudible to normal persons. In meningitis, hydrophobia, the hypnotic state, etc. this condition is observed. Paræsthesiæ are very common, appearing as subjective noises or musical tones (tinnitus aurium) of the most varied kinds (roaring, hissing, blowing, tinkling, whistling, crashing, bell-sounds, etc.), which seem to the subject to be in his ear or in his head. In the present state of our knowledge it is impossible to positively distinguish tinnitus due to local non-nervous ear disease from that which is strictly neural or cerebral in origin. Certainly, intense tinnitus may coincide with complete anæsthesia of the acoustic nerve and a {41} normal state of the middle ear. Theoretically, we may admit tinnitus (corresponding to photopsia in the optic apparatus) as due to an irritative lesion of various parts of the acoustic terminal nervous organ, the acoustic nerve, or the acoustic centre. An acoustic aura (subjective blowing, hissing, etc.) may immediately precede an epileptic attack. Subjective noises may be produced by excitation of the acoustic nerve and terminal organs by the galvanic currents; these galvanic acoustic reactions are regular in the normal condition, and are fully stated in works on electro-therapeutics. Anæsthesia of the acoustic system by peripheral, neural, or central (?) destructive lesions is frequent, and is distinguished from other forms of deafness chiefly by the fact that a sound transmitted through the bones of the cranium (as by a vibrating tuning-fork held against the upper teeth or above the ear) is not heard on one or both sides. Although in a few rare cases the attempt has been made to define nervous deafness for certain sets of notes or as limitations at either end of the musical scale, yet we are not prepared to recognize in neurological practice a condition of partial acoustic anæsthesia corresponding to hemianopsia or achromatopsia. We believe that this progress will be made, however, thus enabling us to locate disturbances in parts of the organ of Corti and in the cortical centre for hearing.