EAR 



1900 



EAR 



person to keep his balance. Nerves extend 

 from them to the cerebellum, communicating 

 there with the nerves controlling the muscles 

 that enable one to stand. Any movement 

 which causes violent or unusual disturbance of 

 the liquid in these canals leads to dizziness, 

 which in turn may cause nausea. Seasickness 

 is caused by this sort of disturbance. 



The Membranous Labyrinth. Within the 

 cavities of the internal ear and separated from 

 the bone by a layer of liquid (perilymph) is a 

 membranous sac which in form and size coin- 

 cides almost exactly with them. To this the 

 name membranous labyrinth has been applied. 

 This sac is filled with fluid (cndolymph) in 

 which are found minute threadlike branches 

 of the auditory nerve. 



The Organ of Corti. The cochlea is divided 

 into two parts, nearly equal in size, by what 

 is known as the basilar membrane. Supported 

 on this is a wonderful structure named, from 

 its discoverer, the organ of Corti. It is formed 



ONE TEST OF HEARING 



This can be comparative only as between two 

 or more people with the same watch. A maxi- 

 mum distance from ear to watch is not easy to 

 suggest, for some watches tick more loudly than 

 others. This test with any time-piece, however, 

 will always demonstrate whether the hearing of 

 one person is more acute than that of another. 



of rods and cells which are continued with the 

 basilar membrane throughout the extent of the 

 cochlea. This organ and the membrane con- 

 stitute a series of vibrating cords provided with 

 nerve apparatus for receiving vibrations which 

 are transmitted from the bones of the ear 

 through the endolymph. These vibrations in 

 turn are transformed into nervous impulses. 

 The cords of the membrane are so adjusted 

 that they can respond to vibrations which vary 

 in rapidity from thirty to about 20,000 each 

 second. The particular part that the organ of 

 Corti plays in the process of hearing is fur- 

 ther explained in the subhead below, How We 

 Hear. 



How We Hear. The act of hearing consists 

 of two parts, one physical and the other men- 

 tal. The apparatus which is described above 

 is for the physical part. That for the mental 



part is found in the auditory centers of the 

 brain, where the sound impressions conveyed 

 by the auditory nerves are perceived and ana- 

 lyzed. To understand how the ear works, one 

 must be acquainted with the laws of sound. 

 These are explained in the article SOUND 

 (which see). This article treats only of the 

 reaction of the ear to sound waves. 



A bell rings in an adjoining room. How do -you 

 hear it? 



1. The tone sent forth is produced by vibrations 

 in the metal of which the bell is made. 



2. These vibrations set up vibrations, or waves, 

 in the air, some of which enter the auditory 

 canal and strike upon the drum membrane. 



3. The waves striking upon the drum membrane 

 set it to vibrating. 



4. These vibrations are carried by the bones of 

 the middle ear to the vestibule, where they set 

 up vibrations in the fluid of the internal ear. 

 The rods in the organ of Corti reproduce these 

 vibrations and excite the auditory nerve, which 

 carries the impression to the auditory centers 

 of the brain. 



5. The auditory centers react ; that is, they 

 bring the mind to bear on the impression they 

 have received, and you hear the bell. 



To obtain an illustration of the the principle 

 upon which the organi of Corti works, stand 

 beside a piano with the lid open, and sing a 

 clear, strong note; then listen, and you will 

 hear the note reproduced by the piano. This 

 is because some wire in the instrument pro- 

 duces the same number of vibrations per second 

 as were produced by the voice. The other 

 wires are silent because they cannot produce 

 this same number of vibrations. The organ of 

 Corti may be likened to a piano with many 

 wires, each selecting the tone it can produce. 



Care of the Ear. The skin of the auditory 

 canal contains cells that pour into the canal 

 a yellowish substance called ear wax, which has 

 a very bitter taste. Its purpose is to protect 

 the ear by catching any dirt that may get into 

 the ear, and to repel insects. The wax dries 

 and scales off and carries foreign substances 

 with it. It should not be removed from the 

 canal except when it accumulates in excess. 

 The ear drum has a very delicate membrane, 

 which is easily punctured or broken. A severe 

 blow upon the ear may break this membrane 

 and render the victim deaf for life; therefore 

 "boxing the ears" of children is a dangerous 

 punishment. Neither should one stick pens or 

 pencils into the ear. It is safe to follow the 

 old German proverb, "Never pick your ear 

 with anything smaller than your elbow." Any 

 foreign substance in the ear should be removed 

 by a physician. 



