Dilatation of the pupil, with insensibility of the retina, exists in amaurosis, and the distinction between blindness resulting from disease of the nerve and that which is consequent on disease of the brain is to be sought in other symp toms of disordered innervation.
The point to be studied is the effect of the sudden admission of light after its exclusion. When no change at all occurs, sight is lost, whether in con traction or dilatation ; but the movement may be so slight as to escape obser vation. In contraction, intolerance of light, or a sense of pain on its admis sion, is to be carefully noted ; in dilatation we have to watch for evidence of the existence of vision when the patient is unable to express his own sensations.
Increased irritability, seen in rapid contraction and full dilatation on the admission or exclusion of light, stands exactly opposed to sluggish action ; the one indicates exalted, the other depressed, nervous energy. It is very re markable how the presence of some object producing an unusual degree of attention in a patient who is listless and depressed, such, for instance, as the entrance of a friend or near relative, may immediately restore the pupils for a time to their normal excitability. Iu examining the condition of the pupil, it is of the greatest importance that light should be excluded from both eyes at the same time, in order to judge correctly of the effect of the stimulus upon either when it is again admitted.
d. Perversions of the sense of vision have less definite relations to conditions of brain. The most important are : (1) double vision, especially when not associated with strabismus, which comes more properly under the head of muscular movements ; and haziusa, of_ikicspartial loss of sight when a portion of an object is lost and seems to be cut off, muscaa voli tantes, and ocular spectra ; (3) hallucinations and illusions, in which unreal objects are seen, or natural objects are clothed in unreal shapes, the constant accompaniments of delirium. The first division is that which demands the most attention, as being probably indicative of cerebral disease; the whole of those classed in the second_ division. Ara-.more, erammonly.caulazved in a thetic or functional4isturbance ; the third are the resu is of de 1 mental alienation ; ocular spectra are distinguished from them by their accompanying states of perfect consciousness and reason, when the evidence of the other senses proves to the individual the non-existence of the object.
§ 3. Indications d,erived from the Sense of Hearing.—These are much less numerous, and, though often dependent on mere local causes, some of them are not without value.
a. Deafness supervening in the course of a febrile attack, as in dicating diminished sensibility of the brain, is almost certainly an evidence that the disease is fever and not inflammation. Ex
treme degrees of deafness are sometimes produced by pressure.
h. Deafness of long, standing in a person suddenly attacked by febrile disorder, should always lead to inquiries into the state of the ear. Disease located there is very apt to excite inflammation within the cranium; it is commonly accompanied by pain and purulent or fetid discharge. For the same reason, when pain is present. we ought to inquire into the existence of deafness, or any other evidence of disease; and thus a history of scarlatina, as antee,edent to the deafness, is very instructive.
c. Intolerance of sound or noise is a valuable symptom of great nervous irritability.
(i. Le.ss importance is to be attached to the existence of tinni tus aurium, of unnatural sounds and noises, or voices. The for mer may exist along with disease of the brain ; the latter are more commonly referable to a mental state; but both are not un frequently the result of mere local affection.
§ 4. Special Alterations of Sensibility.—Perversion and loss of the senses of taste and smell are comparatively unimportant with reference to disease of the brain; they are generally dependent on some morbid condition of the nerve or the mucous membrane. Alterations of common sensation in other organs derive their chief significance from our being able to determine whether the affection be limited to the filamentous extreinities of the nerves, or be produced by some cause acting upon their main trunks, or be connected with disease of the nervous centres. We have to consider the condition of the parts to which the nerve is distri buted, and the relation of the affection to its ramifications. When the sensation is referred to the terminations of one nerve, we have to observe whether any perceptible change of texture in the organ to which it is distributed can account for its existence; when no such cause exists, we have to inquire whether the sensation be limited to the branches of that nerve, or extend to others having a similar origin. Those which have especial reference to the central structures are such as affect the entire half of the body, or extend equally to either side; those limited to the nerves will again occupy our attention (see Chap. XVI.); but it may be here remarked that local fixed pain often accompanies the early stages of chronic disease of the brain, especially in organs not otherwise the subjects of common sensation, such, for example, as hypera3s thesia of the organs of the abdomen. It may be quite impossi ble to show the cause of this connection, and the fact cannot, therefore, be made available for the purposes of diagnosis; but it is well that it should be borne in mind, that its weight may not be lost in considering other symptoms of disease.