(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 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.
(c) Olfactory Apparatus.—Hyperæsthesia of this sense is at present considered more a personal peculiarity than as a symptom of disease. Paræsthesiæ show themselves as subjective odors of various sorts, and when transient may be an olfactory aura preceding epileptic attacks. In conditions of organic disease subjective odors may coincide with complete loss of smell. Anæsthesia of the olfactory nervous apparatus may be due to (1) strictly local disease in the nose, catarrh, etc.; (2) to anæsthesia of the trigeminus nerve and consequent local lesions; (3) to a truly nervous lesion affecting the olfactory nerves, the olfactory bulbs, the olfactory tracts, or, lastly, the cortical centre for smell (at present unknown in man). The two last morbid conditions are usually unilateral, and coexist with subjective odors.
(d) Gustatory Apparatus.—In this sense hyperæsthesia is clinically unknown, though as a result of education extreme delicacy of taste, a relative hyperæsthesia, may be produced. Paræsthesiæ are rare. In two cases in which we have observed the symptom (one of neurasthenia, the other of hypochondriacal melancholia) it consisted in a constant and most distressing sweet taste. The application of the galvanic current at the base of the brain, under the jaw, on the cheeks, and within the mouth produces subjective tastes of an acid or metallic nature. Anæsthesia of the gustatory nerve occurs after section of the lingual branch of the trigeminus—an operation sometimes done for lingual neuralgia, in which case the frontal two-thirds of the tongue on one side loses its property of perceiving taste. As the result of central disease next to nothing is known of this symptom. It is probable that sweet and acid tastes are perceived in the mouth and forward part of the tongue; bitter tastes on its caudal (posterior) third and in the throat (glosso-pharyngeal nerve). In the insane, paræsthesiæ and anæsthesia give rise to a great variety of delusions about the state of the parts, the nature of their food, poison in the food, etc.
As a part of typical complete hemianæsthesia the special senses are involved. When of hysterical origin the whole retina of one eye is generally devoid of sensibility, or it does not perceive colors. When the hemianæsthesia is due to a lesion of the caudal part of the internal capsule (organic anæsthesia), we should expect to find lateral hemianopsia, with dark half-fields on the same side as the cutaneous anæsthesia. We would not be understood as claiming that this point of distinction is as yet positively determined, but would advance it suggestively, subject to the result of observations on new cases.
III. Motory Symptoms.
PARALYSIS, or AKINESIS, is a condition in which loss of voluntary or involuntary muscular movement occurs through defective innervation. Such a strict definition is desirable, as excluding cases in which motion is abolished by local or general morbid states not essentially nervous, as in acute articular rheumatism, ruptures of muscles or tendons, fractures, extreme asthenia, etc.
Paresis is a term often employed to designate a paralysis partial in degree; it does not mean an essential muscular paralysis.
Paralysis varies infinitely in extent and distribution, yet certain types are recognized as having diagnostic value, and their exact determination is of great importance in practice.
(a) Hemiplegia, or paralysis of many muscular groups in one lateral half of the body.
(α) Common Hemiplegia.—In this, the most frequent form, we find loss of voluntary motion in many muscles of one side of the face and body. This condition may or may not be preceded by apoplectic or epileptic symptoms: it may occur gradually or suddenly. Although it is customary to say that in hemiplegia a patient is paralyzed on one side, this is not strictly correct, as careful observation shows that (1) in the face only the lower facial muscles are distinctly affected; the tongue itself is rarely paralyzed, but its projecting muscular apparatus is, so that when protruded it deviates as a whole toward the paralyzed side; the eye-muscles and masticatory muscles are unaffected; (2) in the extremities the loss of power is greatest in the hand and foot, less so in the arm and thigh, very slight in the muscular groups of the shoulders and hips; (3) the muscles of the neck and trunk, the respiratory muscles, and in general the muscles of the vegetative life are practically unaffected. These facts may be summarized by the statement that in common hemiplegia the greatest paralysis is shown in those muscular groups whose action is most independent on either side of the body; or, in other words, in those whose functions are most highly differentiated and whose innervation is most cortical (from the motor centres in the cerebral cortex). Those muscular groups, on the other hand, whose action is usually or necessarily simultaneously bilateral or associated across the median line—or, in other words, whose innervation is largely spinal or subcortical—are least paralyzed; while the purely automatic or reflex muscular apparatuses, those having a strictly spinal or sympathetic innervation, are not at all affected.