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Nervous Deafness.The perception of a sound involves a somewhat complicated process. As it ordinarily occurs, this process is as follows: The vibrations of the air cause a tremor of the curtain which is placed across the inner end of the bony channel of the external ear ; there lies in contact with the inner surface of this membrane a small bone shaped like a hammer ; this is the first of a chain consisting of three small bones lying in such close contact that a slight movement of one is communicated to the other. The third bone of this chain lies in contact with another membrane, which closes a bony channel filled with fluid. In this fluid-arranged in a somewhat peculiar way-rest the ends of the nerves of hearing. A vibration therefore which sets the membrane of the drum of the ear in a tremor, is transmitted along these bones to the membrane closing the inner bony canal, and through this membrane it is communicated to the liquid in which the nerve-ends lie. The effect produced upon these nerve ends by the little wave into which this liquid is thrown, causes in the individual the perception known as hearing. In order that this effect shall cause an impression upon the consciousness, it must be transmitted along the nerves of hearing to the brain. It is evident, therefore, that there are many opportunities for derangements of an apparatus so complicated as this. Some of these have been already mentioned. A catarrh of the middle ear, for instance, causes such a thickening of the membrane of the drum that it does not vibrate so readily, and hence does not transmit sound to the nervous apparatus. An accumulation of wax in the external ear causes deafness by preventing the air from reaching the membrane of the drum. There are also diseases which affect the nervous part of the apparatus and cause deafness, although the drum of the ear and all its belongings may be perfectly healthy and in natural condition. Such cases are, therefore, termed nervous deafness. Such instances usually occur as the result of diseases affecting the brain and the membranes which cover it. Thus deafness is frequently the result of " inflammation of the brain " and of cerebrospinal meningitis. It occurs, too, as a sequel to scarlet fever, and to other infectious diseases. Symptoms.- Nervous deafness can be recognized as such only by the absence of all symptoms which would indicate a disease of the other parts of the ear. When it is found, upon close examination, that the membrane of the drum of the ear, as well as this cavity itself, and the various channels leading to it are all in a perfectly natural condition, it may be inferred that whatever deafness exists is due to disease of the nerves concerned in hearing. This suspicion is in most cases confirmed by the history of the patient, since he has usually suffered from brain fever or other severe disease which is known to occasion destruction of the sense of hearing. Such an opinion can, of course, be established only by a surgeon ; yet the non-professional observer can usually form a pretty accurate idea of the nature of the deafness in the following simple way. The individual is, we will suppose, quite deaf in one or both ears-usually in both, if the deafness be of nervous origin. Now, let a tuning fork be struck against the table, and its handle held to the teeth of the individual, or placed against the head just behind the ear. If the cause of the deafness be located elsewhere than in the nervous part of the apparatus, the individual will now hear far more distinctly than when the tuning fork is merely held near the ear without touching it. If, on the contrary, the difficulty be located in the nervous apparatus, the patient will not observe any marked difference when the tuning fork is held in contact with the head. The reason for this is, of course, evident. The nerves are the organs absolutely essential to hearing ; the bony part of the ear and the membrane of the drum are valuable merely to conduct the waves of air so that they shall affect these nerves. Now, vibrations are also well conducted by the bones of the head, and therefore by the teeth ; hence^ if the individual hears decidedly better when the tuning fork is placed against the bones of the head than he did before, it is evident that the fault is in that part of the hearing apparatus whereby the vibrations are transmitted to the nerves, and not in these structures themselves ; if, on the other hand, the patient can not hear distinctly when the tuning fork is held to the teeth, it is evident that the fault must lie, not in the conducting apparatus, but in the nerves themselves. Treatment* - When it is definitely decided that the deafness results from disease of the nerve structures of long standing, all treatment may be abandoned ; no means are known whereby these diseased nerves can be restored to their natural condition. Almost all the drugs known to the profession, and all other means, including electricity, have been employed in vain to remedy this unfortunate condition. Yet it should never be assumed that this is actually the cause of the deafness until no further possibility of doubt remains ; if the disease be located in any other part of the ear, there is always hope that faithful and persistent employment of proper remedies qiay at least improve, if not entirely relieve the deafness. But first, if you want to come back to this web site again, just add it to your bookmarks or favorites now! Then you'll find it easy! Also, please consider sharing our helpful website with your online friends.
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