Bristol news. [volume] (Bristol, Va. & Tenn.) 1867-189?, 1878-12-03
Written for the Bristol News.
Physiology for Practical Use.
BY JAS. D. BRAGG, NJ. D., MARION, VA.
| CONTINUED.

The drum of the ear is almost trans
parent, and though moderately strong,
is little thicker than gold-beater's
skin. Being kept gently on the
stretch, it thrills to every whisper, and
two small muscles keep it in the most
delicate adjustment to each varying
impulse with which the air comes la
den. One Of these muscles draws it
tighter, the other looSens it by acting
upon a chain of very small bones
which pass, suspended as it were in
mid-air, and swinging with every
breath across the drum, from the
membrane to the nerve. This chain
of bones answers two purposes: First,
it receives vibrations from the men,
brane and conveys them to the laby-
rinth ; secondly, it adjusts both the
membrane, and the fluid which sur
rounds the nerve, to the various kinds
and pitches Of sound by which they
are affected. Besides the membrane
already described, there is a second
smaller membrane opposite to it; that
is, on the inner wall of the drum,
which closes the spiral canal before
mentioned, in which one part of the
nerve is spread out. The use of this
second membrane is not yet fully de-
tr,mineG Lastly, a tube leads from
the drum into the throat, called, from
its discoverer, Enstachius, the EuSta-
chan tube. The use Of this tube is
two-fold: First, it supplies the drum
with air, and keeps the membrane ex-
actly balanced and free to move with
equal air-pressure on each side, and
bre0ents it from 6eIng ehOked BY its O7on
moisture 1t is not always open, how
ever, but is opened by the act of swal-
lowing by little muscle which is at
tached to it just as it reaches the
throat. Most persons can distinctly
feel that this is the case by gently
closing the nose and swallowing !;
when = distant sensation is felt in
the ears. This sensation is due to
little air bsing drawn out Of the ears
through the open Tube during swal-
lowing aud it lasts for few minutes
unless the air is again restored by
swallowing With the nose Enclosed,
which allows for the moment q free
communication between the ear and
the throat. We thus see 9 reason
for the tube being closed. lit we're
always open all the sounds produced
in the throat would pass directly into
the drum Of the ear, and totally con-
fuse us. We should hear every
breath, and live in constant bewil-
derment Of internal sounds. At the
same time the closure, being but
light contact Of the walls of the tube.
easily allows q slight escape of air
from the drum, and thus not only IA
cilitates AMI regulates the oscillations
of the air before the vibrating men
brsne, but provides = safety valve, to
a certain extent, against the injurious
influence of loud sounds. TIE chief
use of The Eustachian tube is to allow
free Interchange of air between the
ear and the throat, aud this is OK
ceedingly important aud it is veIy
important also that its use in this re-
spect should be understood, Persons
who go down in diving>hells soon be-
gin to feel a great pressure in the
ears, and if the depth is great, the
feeling becomes extremely painful.
This arises from the fact, that in the
sub marine vessel the pressure Of the
air is increased, in order to balance
the weight of the wafer above and
thus it presses with great force upon
the membrane of the drum, which. if
the Eustachian tube has been kept
closed, has only the ordinary uncom-
pressed air in the inner side to Sus-
tain il