ly small particles of which the
odor of various bodies is composed come in contact with the minute
ramifications of the olfactory nerve that this sensation is produced. In
order to protect these sensitive nerves, as well as to prevent the
introduction into the lungs of injurious substances, the air-passages of
the nose are furnished with hairy appendages, which are less or more
abundant according to the size of these passages. These intercept any
foreign substances that enter the nose, and thus irritate the mucous
membrane, and cause a quick and powerful contraction of the diaphragm,
by which the offending matter is immediately expelled. This phenomenon,
which is called sneezing, depends upon a connection of the olfactory
with the respiratory nerves.

This sense not only comes in to the aid of taste in enabling man and the
lower animals to select proper food, and avoid that which is injurious,
but it also gives us positive and varied pleasure by the inhalation of
agreeable odors, while, at the same time, it enables us to avoid an
infectious atmosphere, and all objects whose odors are offensive and
hurtful.

It is true that man can accustom himself to nearly all kinds of odor,
even to those that at first are very disagreeable. He indeed not
unfrequently so vitiates the sense of smell as actually to prefer those
scents which, to persons who have preserved the integrity of this sense,
are regarded as exceedingly offensive, and even filthy. But why, let me
ask, did the Creator give us the sense of smell? Was it to be thus
perverted? No, indeed: it was, without doubt, that we might enjoy the
refreshing fragrance of flowers and herbs, of food and drink; and also
that we might distinguish between air that is pure and healthful, and
that which is impure and infectious. As most articles of food which are
agreeable to the smell are wholesome, and as those which are
disagreeable are generally unwholesome, so, also, those states of the
atmosphere which are grateful to this sense are salubrious, and those
odors which are pleasant are healthful, while air which is ungrateful
will generally be found injurious to health, as will also all those
odors which are unpleasant to this sense when in a healthful state. He
who has had occasion to enter a crowded court-room, lecture-room,
church, or assembly-room of whatever kind, which has been occupied for a
considerable time without adequate ventilation, can not fail to remember
the unwelcom