another channel for its entrance into the ear through the eustachian
tube, But Dr. W. Ogle[1206] has been so kind as to search the best
recent authorities on the functions of the eustachian tube, and he
informs me that it is almost conclusively proved that it remains closed
except during the act of deglutition; and that in persons in whom the
tube remains abnormally open, the sense of hearing, as far as external
sounds are concerned, is by no means improved; on the contrary, it is
impaired by the respiratory sounds being rendered more distinct. If a
watch be placed within the mouth, but not allowed to touch the sides,
the ticking is heard much less plainly than when held outside. In
persons in whom from disease or a cold the eustachian tube is
permanently or temporarily closed, the sense of hearing is injured; but
this may be accounted for by mucus accumulating within the tube, and
the consequent exclusion of air. We may therefore infer that the mouth
is not kept open under the sense of astonishment for the sake of
hearing sounds more distinctly; notwithstanding that most deaf people
keep their mouths open.
Every sudden emotion, including astonishment, quickens the action of
the heart, and with it the respiration. Now we can breathe, as
Gratiolet remarks[1207] and as appears to me to be the case, much more
quietly through the open mouth than through the nostrils. Therefore,
when we wish to listen intently to any sound, we either stop breathing,
or breathe as quietly as possible, by opening our mouths, at the same
time keeping our bodies motionless. One of my sons was awakened in the
night by a noise under circumstances which naturally led to great care,
and after a few minutes he perceived that his mouth was widely open. He
then became conscious that he had opened it for the sake of breathing
as quietly as possible. This view receives support from the reversed
case which occurs with dogs. A dog when panting after exercise, or on a
hot day, breathes loudly; but if his attention be suddenly aroused, he
instantly pricks his ears to listen, shuts his mouth, and breathes
quietly, as he is enabled to do, through his nostrils.
When the attention is concentrated for a length of time with fixed
earnestness on any object or subject, all the organs of the body are
forgotten and neglected;[1208] and as the nervous energy of each
individual is limited in amount, little is transmitted to any part of
the system, excepting that which is at the time brought into energetic
action. Therefore many of the muscles tend to become relaxed, and the
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