erves are much the same as
those of alcohol. Tobacco is very injurious to the mind.

8. Tobacco-using often leads boys to drunkenness and other vices.

9. The use of opium and chloral produces even worse effects than the use
of alcohol or tobacco.

CHAPTER XXV.

HOW WE HEAR, SEE, SMELL, TASTE, AND FEEL.

~1. The Senses.~--We have five senses--_hearing_, _seeing_, _smelling_,
_tasting_, and _feeling_. These are called special senses because they
are very different from each other. They also differ from the general
sense of feeling by means of which we feel pain when any part is hurt.

~2. Organs of the Special Senses.~--Each of the special senses has a
special set of nerves and also special cells in the brain which have
charge of them. We say that we see with our eyes, hear with our ears,
feel with our fingers, etc.; but, really, we see, hear, taste, and smell
in the brain just as we feel in the brain. The eyes, ears, nose, and
other organs of the special senses are the instruments by means of which
the brain sees, hears, smells, etc.

~3. Sound and the Vibrations which it Causes.~--All sounds are made by
jars or vibrations of objects. Sounds cause objects to vibrate or
tremble. A loud sound sometimes jars a whole house, while other sounds
are so gentle and soft that we cannot feel them in the same way that we
feel loud sounds. But Nature has made for us an ingenious organ by means
of which we can feel these very fine vibrations as well as loud ones. We
call this organ the _ear_.

~4. The Ear.~--The part of the ear which we can see is shaped somewhat
like a trumpet. The small opening near the middle of the ear leads into
a _canal_ or tube which extends into the head about an inch. At the
inner end there is a curious little chamber. This is called the _drum_
of the ear, because between it and the canal of the ear there is
stretched a thin membrane like the head of a drum. The ear-drum is also
called the _middle ear_.

[Illustration: THE EAR.]

~5. Bones of the Ear.~--Within the drum of the ear there are three
curious little bones which are joined together so as to make a complete
chain, reaching from the drum-head to the other side of the drum. The
last bone fits into a little hole which leads into another curious
chamber. This chamber, which is called the _inner ear_, is filled with
fluid, and in this fluid the nerve of hearing is spread out. A part of
the inner ear looks very much like a snail shell.