SENSE OF SMELL.
876. This sense is located in the air-passages of the _Nose_. To
understand the function of smell, the structure of the nose and nasal
cavities, with the distribution of the olfactory nerves, must be first
examined.
ANATOMY OF THE ORGANS OF SMELL.
877. The NOSE is composed of the _Bones_, _Fi'bro-car'tilages_, and
_Mu'cous Mem'brane_, together with its integuments.
878. The BONES of the nose are the nasal, and the nasal processes of
the upper jaw.
879. The FIBRO-CARTILAGES give form and stability to the framework of
the nose, providing at the same time, by their elasticity, against
injuries. They are five in number.
880. The MUCOUS MEMBRANE, which lines the interior of the nose, is
continuous with the skin externally, and with the lining membrane of
the parts of the throat. The entrance of the nostrils is provided with
numerous hairs, which serve as guardians to the delicate membrane of
the nose.
881. The NASAL FOSSAE, or nostrils, are two irregular, compressed
cavities, extending from the nose to the pharynx. These cavities are
bounded superiorly by the sphenoid and ethmoid bones; inferiorly, by
the hard palate. In the middle line they are separated from each other
by a bony and fibro-cartilaginous septum; upon the outer wall of each
fossa, in the dried skull, are three projecting processes, termed
spongy bones. In the fresh fossa, these are covered by a mucous
membrane.
-=-=-=-=-=-=-=-=-=-=-=-=
876. Where is the sense of smell located? 877-884. _Give the anatomy
of the organs of smell._ 877. Name the parts that enter into the
structure of the nose? 878. What bones form the framework of the nose?
879. What is the use of the cartilages? 880. What relation has the
mucous membrane with other membranes of the nose? 881. Describe the
nasal cavities.
-=-=-=-=-=-=-=-=-=-=-=-=
882. The space that intervenes between the superior and middle spongy
bone, is called the _superior me-a'tus_, or channel; the space between
the middle and inferior bone, is the _middle meatus_; and that between
the inferior bone and the floor of the fossa, is the _inferior
meatus_.
[Illustration: Fig. 135. A vertical section of the middle part of the
nasal cavities. 7, The middle spongy bones. 8, The superior part of the
nasal cavities. 10, The inferior spongy bones. 11, The vomer. 12, The
upper jaw. 13. The middle channel of the nose. 14, The lower channel of
the nose. 17, The palatine process of the upper jaw-bone. 18, The roof of
the mouth covered by mucous membrane. 19, A section of this membrane.]
883. The MEATUSES are passages that extend backward, from the
nostrils, into which are several openings. They are lined by a mucous
membrane, called the _pi-tu'i-ta-ry_, or _schneiderian_, from
Schneider, who first showed that the secretion of the nasal fossae
proceeded from the mucous membrane, and not from the brain.
-=-=-=-=-=-=-=-=-=-=-=-=
882. What terms are applied to the spaces between these processes?
What does fig. 135 represent? 883. Define the meatuses. By what are
they lined?
-=-=-=-=-=-=-=-=-=-=-=-=
884. Upon the mucous membrane of the nasal passages, the olfactory
nerve ramifies, and also a branch of the fifth pair of nerves. This
membrane is of considerable extent in man; and in those animals whose
sense of smell is very acute, it is still more extensive.
[Illustration: Fig. 136. A side view of the passage of the nostrils, and
the distribution of the olfactory nerve. 4, The olfactory nerve. 5, The
fine and curious divisions of this nerve on the membrane of the nose. 6,
A branch of the fifth pair of nerves.]
PHYSIOLOGY OF THE ORGANS OF SMELL.
885. The sense of smell enables us to discern the odor or scent of any
thing. When substances are presented to the nose, the air that is
passing through the nostrils brings the odoriferous particles of
matter in contact with the filaments of the olfactory nerves, that are
spread upon the membrane that lines the air-passages, and the
impression is then transmitted to the brain.
-=-=-=-=-=-=-=-=-=-=-=-=
884. What nerves ramify upon this membrane? What is represented by
fig. 136? 885-899. _Give the physiology of the organs of smell._ 885.
How does the mind become sensible of odoriferous particles?
-=-=-=-=-=-=-=-=-=-=-=-=
886. This sense, with that of taste, aids man as well as the inferior
animals, in selecting proper food, and it also gives us pleasure by
the inhalation of agreeable odors. The sense of smell, like that of
taste and touch, may be improved by cultivation. It likewise varies in
different persons.
_Observation._ Sometimes this sense seems to possess a morbid degree
of acuteness in respect to odors, which is highly inconvenient and
even dangerous. With some individuals, the smell of certain fruits,
flowers, cheese, &c., produce nausea and even convulsions.
887. In the inferior animals generally, the sense of smell is more
acute than in man. Thus the bloodhound will track the hare over
the ground for miles, guided only by the odor that it leaves in
its flight. He also traces the progress of his master through
thickly-crowded streets, distinguishing his footsteps from those of
a thousand others, and amidst the odorous particles emanating from a
thousand sources.
_Observation._ In some of the higher orders of the inferior animals,
there is an astonishing acuteness of smell in regard to effluvia that
come from living animals. To these animals, it possesses an importance
in them far beyond what it has in man, by making them acquainted with
the presence of their enemies or their prey, when the eye and ear are
incapable of acting. It is related by travellers in Africa, that they
were always apprised of lions in their vicinity during the night, by
the moans and tremblings of their horses.
888. Smell is somewhat under the control of the will. That is, we
have the power of receiving or rejecting odors that are presented;
thus, if odors are agreeable, we inspire forcibly, to enjoy them; but,
if they are offensive, our inspirations are more cautious, or we close
our nostrils. This sense is likewise modified by habit; odors which,
in the first instance, were very offensive, may not only become
endurable, but even agreeable.
-=-=-=-=-=-=-=-=-=-=-=-=
886. What is the use of the sense of smell? Can this sense be
improved by cultivation? What is said respecting this sense in some
individuals? 887. What is said of this sense in the bloodhound?
Mention an instance of astonishing acuteness of smell in some of
the higher orders of animals. 888. Show that smell is somewhat under
the control of the will.
-=-=-=-=-=-=-=-=-=-=-=-=
889. Acuteness of smell requires that the brain and nerve of smell be
healthy, and that the membrane that lines the nose be thin and moist.
Any influence that diminishes the sensibility of the nerves, thickens
the membrane, or renders it dry, impairs this sense.
_Observations._ 1st. _Snuff_, when introduced into the nose, not only
diminishes the sensibility of the nervous filaments, but thickens the
lining membrane. This thickening of the membrane obstructs the passage
of air through the nostrils, and thus obliges "snuff-takers" to open
their mouths when they breathe.
2d. The mucous membrane of the nasal passages is the seat of chronic
catarrh. This affection is difficult of removal, as remedial agents
cannot easily be introduced into the windings of these passages. Snuff
and many other articles used for catarrh, produce more disease than
they remove.
-=-=-=-=-=-=-=-=-=-=-=-=
889. On what does acuteness of smell depend? What effect has snuff
when introduced into the nose? What is said of chronic catarrh?
-=-=-=-=-=-=-=-=-=-=-=-=