carried to the brain by the auditory nerve.
The sensation of hearing, like that of sight, gives us two qualities: namely, tones
with their accompanying pitch and timbre, and noises. Tones, or musical sounds,
are produced by isochronous or equal-timed vibrations; thus C of the first octave
is produced by 256 vibrations a second, and if this tone is prolonged the
vibration rate will continue uniformly the same. Noises, on the other hand, are
produced by vibrations which have no uniformity of vibration rate. The ear's
sensibility to pitch extends over about seven octaves. The seven-octave piano
goes down to 27-1/2 vibrations and reaches up to 3,500 vibrations. Notes of
nearly 50,000 vibrations can be heard by an average ear, however, though these
are too painfully shrill to be musical. Taking into account this upper limit, the
range of the ear is about eleven octaves. The ear, having given us loudness of
tones, which depends on the amplitude of the vibrations, pitch, which depends
on the rapidity of the vibrations, and timbre, or quality, which depends on the
complexity of the vibrations, has no further qualities of sound to reveal.
Taste.—The sense of taste is located chiefly in the tongue, over the surface of
which are scattered many minute taste-bulbs. These can be seen as small red
specks, most plentifully distributed along the edges and at the tip of the tongue.
The substance tasted must be in solution, and come in contact with the nerve
endings. The action of the stimulus is chemical.
The sense of taste recognizes the four qualities of sour, sweet, salt, and bitter.
Many of the qualities which we improperly call tastes are in reality a complex of
taste, smell, touch, and temperature. Smell contributes so largely to the sense of
taste that many articles of food become "tasteless" when we have a catarrh, and
many nauseating doses of medicine can be taken without discomfort if the nose
is held. Probably none of us, if we are careful to exclude all odors by plugging
the nostrils with cotton, can by taste distinguish between scraped apple, potato,
turnip, or beet, or can tell hot milk from tea or coffee of the same temperature.
Smell.—In the upper part of the nasal cavity lies a small brownish patch of
mucous membrane. It is here that the olfactory nerve endings are located. The
substance smelled must be volatile, that is, must exist in gaseous form, and come
in direct contact with the nerve endings. Chemical action results in a nerve
current.
The sensations of smell have not been classified so well as those of taste, and we
have no distinct names for them. Neither do we know how many olfactory