, 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.

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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?

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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 presen