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Hearing and Ears

by Dennis Nolan

The ear is an organ that is used for hearing. 

In some of the lower animals, the ear can be seen in its simplest form.  This shows that the ear is simply a sac of liquid, in which the end of the auditory nerve is expanded. 

The ears of the locus are situated on each side of the basal joint of the abdomen.  The green grasshoppers and katydids hear through ears situated on their front legs.  These ears look like little scars.  The mosquito is believed to hear through sensitive spots on its antennae or feelers. 

The human ear on the other hand is rather complex.  It consists of three divisions: 

- The outer, or external ear

The peculiar folds and passages of the outer ear are of service in catching sound, and also in enabling the herer to determine from what direction it comes.

- The middle ear

The middle ear is an air chamber communicating with the throat by an air passage or tube, called the eustachian tube.  The ear chamber is seperated from the outer and from the inner ear by membranes giving it the structure of a drum.  Three small, movable bones, called the bones of the ear, reach from the outer membrane to the inner. 

- The inner ear or labyrinth. 

The inner ear, or labyrinth, is filled with liquids.  The auditory nerve, which comes from the brain, terminates here. 

Sound reaches the brain as follows:  The vibrations of the atmosphere set the outer membrane in motion.  This agitates the bones of the ear.  They set up a vibration in the inner membrane, which, in turn, shakes the liquids in the labyrinth, thus disturbing the end of the auditory nerve, along which the sensation flies to the brain. 

A forceful vibration gives the impression of a loud noise.  If agreeable vibrations come frequently, they give the impression of music. 

The human ear is able to note a sound having a frequency of from 32 to 38,000 vibrations per second.  A rare ear can go to 50,000.  The ear of a cat is capable of hearing an extraordinarily high note.  No doubt the world, especially the insect world, is full of sounds quite intelligible to many ears, but unknown to the human ear. 

The linings and the membrane of the outer ear are kept moist by the excretion of ear wax.  When, as often happens, especially in old age, the membrane becomes dry and inflexible, and thus unable to vibrate, partial deafness ensues.  Usually a person with defective hearing can use a hearing device that will increase the intensity of sound waves for them.


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