A consideration of deafness requires some understanding of the structure and relations of the ear with other parts of the body, notably the throat. It has been pointed out that the external ear comprising the fleshy portion of the ear, or auricle, and the opening, or canal, about an inch long is separated from that portion of the ear within (or middle ear) by the drum membrane. The middle ear, while protected from the outer air by the drum, is really a part of the upper air passages, and participates in disorders affecting them. It is the important part of the ear as it is the seat of most ear troubles, and disease of the middle ear not only endangers the hearing, but threatens life through proximity to the brain.
In the middle ear we have an air space connected with the throat by the Eustachian tube, a tube about an inch long running downward and forward to join the upper air passage at the junction of the back of the nose and upper part of the throat. If one should run the finger along the roof of the mouth and then hook it up behind and above the soft palate one could feel the openings of these tubes (one for each ear) on either side of the top of the throat or back of the nose, according to the view we take of it.
Then the middle ear is also connected with a cavity in the bone back of the ear (mastoid cavity or cells), and the outer and lower wall is formed by the drum membrane. Vibrations started by sound waves which strike the ear are connected by means of a chain of three little bones from the drum through the middle ear to the nervous apparatus in the internal ear. The head of one of these little bones may be seen by an expert, looking into the ear, pressing against the inside of the drum membrane. Stiffening or immovability of the joints between these little bones, from catarrh of the middle ear, is most important in producing permanent deafness. The middle ear space is lined with mucous membrane continuous with that of the throat through the Eustachian tube. This serves to drain mucus from the middle ear, and also to equalize the air pressure on the eardrum so that the pressure within the middle ear shall be the same as that without.
When there is catarrh or inflammation of the throat or nose it is apt to extend up the Eustachian tubes and involve the middle ear. In this way the tubes become choked and obstructed with the oversecretion or by swelling. The air in the middle ear then becomes absorbed in part, and a species of vacuum is produced with increased pressure from without on the eardrum. The drum membrane will be pressed in, and through the little bones pressure will be made against the sensitive nervous apparatus, irritating it and giving rise to deafness, dizziness, and the sensation of noises in the ear. Noises from without will also be intensified in passing through the middle ear when it is converted into a closed cavity through the blocking of the Eustachian tube.
A very important feature following obstruction of the Eustachian tubes, and rarefaction of the air in the middle ear, is that congestion of the blood vessels ensues and increased secretion, because the usual pressure of the air on the blood vessels within the middle ear is taken away.
This then is the cause of most permanent deafness, to which is given the name catarrhal deafness, because every fresh cold in the head, or sore throat, tends to start up trouble in the ear such as we have just described. Repeated attacks leave vestiges behind until permanent deafness remains. In normal conditions every act of swallowing opens the apertures of the Eustachian tubes in the throat, and allows of equalization of the air pressure within and without the eardrum, but if the nose is stopped up by a cold in the head, or enlargement of the tonsil at the back of the nose (as from adenoids), the process is reversed and air is exhausted from the Eustachian tubes with each swallowing motion.
The moral to be drawn from all the foregoing is to treat colds properly when they are present, keeping the nose and throat clean and clear of mucus, and to have any abnormal obstruction in the nose or throat and source of chronic catarrh removed, as enlarged tonsils, adenoids, and nasal outgrowths.