Experiment 160.  Listen to a ticking watch or a tuning-fork kept vibrating electrically.  Close the mouth and nostrils, and take either a deep inspiration or deep expiration, so as to alter the tension of the air in the tympanum; in both cases the sound is diminished.

Experiment 161.  With a blindfolded person test his sense of the direction of sound, e.g., by clicking two coins together.  It is very imperfect.  Let a person press both auricles against the side of the head, and hold both hands vertically in front of each meatus.  On a person making a sound in front, the observed person will refer it to a position behind him.

347.  Practical Hints on the Care of the Ear.  This very delicate and complicated organ is often neglected when skilled treatment is urgently needed, and it is often ignorantly and carelessly tampered with when it should be let alone.

Never insert into the ear canal the corners of towels, ear spoons, the ends of toothpicks, hairpins, or any other pointed instruments.  It is a needless and dangerous practice, usually causing, in time, some form of inflammation.  The abrasion of the skin in the canal thus produced affords a favorable soil for the growth of vegetable parasites.

[Illustration:  Fig. 143.—­Diagram of the Middle and Internal Ear.]

This, in turn, may lead to a chronic inflammation of the canal and of the tympanic membrane.  Again, there is always risk that the elbow may be jogged and the instrument pushed through the drum-head.  There is, of course, a natural impulse to relieve the itching of the ear.  This should be done with the tips of the fingers or not at all.

The popular notion that something should be put into the ear to cure toothache is erroneous.  This treatment does not cure a toothache, and may lead to an injury to the delicate parts of the ear.  A piece of absorbent cotton, carefully inserted into the ear, may be worn out of doors, when the cold air causes pain, but should be removed on coming into the house.

Frequent bathing in the cold water of ponds and rivers is liable to injure both the ears and the general health.  In salt-water bathing, the force of the waves striking against the ears often leads to earache, long-continued inflammation, or defective hearing; to diminish this risk, insert into the ears a small plug of absorbent cotton.

The ears are often carelessly exposed to cold water and inclement weather.  Very cold water should never be used to bathe the ears and nostrils.  Bathe moderately and gently in lukewarm water, using a wash-rag in preference to a sponge; dry gently and thoroughly.  Children’s ears are often rudely washed, especially in the auditory canal.  This is not at all necessary to cleanliness, and may result in a local inflammation.

Never shout suddenly in a person’s ear.  The ear is not prepared for the shock, and deafness has occasionally resulted.  A sudden explosion, the noise of a cannon, may burst the drum-head, especially if the Eustachian tube be closed at the time.  During heavy cannonading, soldiers are taught to keep the mouth open to allow an equal tension of air.