by the bones of the spine, through distinct
holes in which the nerves severally emerge
between thick layers of muscle. Yet they
are frequently injured by accident and
disease. A broken back causes complete
paralysis of all the parts whose nerves arise
below the seat of injury. But it is not
unusual for disease of the spine to paralyse
one set of roots, while the other retains its
power. The consequences are sometimes
amusing. A French soldier one day took
the lid from a frying-pan when it was nearly
red hot, and never felt that it was burning him.
In this case the posterior roots were paralysed.
When a man's legs are affected in this way,
he will be able to walk only while he sees
his legs, and direct their movements by his
will. Let his attention be diverted for a
moment and he falls down.

These spinal nerves have, on their sensitive
roots, a small swelling called a ganglion;
and the fifth nerve which arises from the
brain has also two roots, on one of which is
a ganglion, being in every respect similar to
the spinal nerves. These together form a
nervous system, which is essential to all
animals who have to seek their food. It
supplies the arms and legs for moving, in
search of, and grasping the food, and the
mouth, and tongue, and other organs which
are exercised in swallowing. So complete
is this system in itself that the nerve of
taste, instead of being a special nerve like
the nerve of the eye or ear, is a branch of
the fifth nerve; taste being absolutely
essential to the selection of food. Sight, smelling,
and hearing are additions to this system in
the higher animals, and have their special
nerves.

The sympathetic system consists of a
number of ganglions placed among the abdominal
organs, and on either side of the back bone,
with tendrils connecting them to each other,
and to the spinal nerves; giving branches
to all neighbouring parts, especially to the
internal organs. The arrangement of these
ganglions may be compared to a row of
strawberry roots on each side of the spine, with
their connecting tendrils; only the ganglions
are not roots. The system has no origin; it
is spread over all the body; but its centre
is in the pit of the stomach, where a blow is
more immediately fatal than on the head
itself. Boxers know well enough the blow
which most effectually doubles up their
opponent.

Wonderful are the offices which the
sympathetic system fulfils in the animal
economy. By the vitality which it supplies,
processes are carried on by the various
organs which no chemist in his laboratory
can rival. The stomach selects the nutritive
parts of the food, and rejects the unprofitable.
The food is converted into blood; the
liver and kidneys eliminate noxious particles,
and that wonder of wonders, nutrition of the
whole body, takes place; the same material
being formed at one spot into bone, at another
into muscle and nail—into all the various
parts of the body, each in its place.

The connections of the sympathetic with
the spinal nerves and the fifth account for
the pain felt in remote parts when the cause
is in the internal organs. Tic, which is an
affection of the fifth nerve, is almost always
so caused, and is never relieved by cutting
the nerve, because the pain of an injured
nerve, wherever the seat of injury may be,
is always referred to its extremities. A man
after his leg has been cut off will feel perfectly
his knee, ancle, and toes; and he will
sometimes use his hands to lift his lost knee over
the one he has left.

The nerves of the special senses come from
the brain. There is a distinct nerve on each
side for the senses of smelling, seeing, and
hearing. The nerve of taste, as I have
mentioned, is a branch of the fifth, as it would
seem to render that system quite complete.
Their peculiarities are indicated by their
names. They are quite insensible to pain.
Irritate the optic nerve, and the consequence
is a flash of light. The sensitiveness of the
eye is given by branches of the fifth, and its
movements are regulated by three nerves
from the brain which are exclusively
distributed to the muscles of the eye.
Altogether no less than six nerves are supplied to
this important organ. The optic nerve, being
the only nerve of sight, makes us uncommonly
sceptical when the mesmerists talk about
reading with the pit of the stomach.
Sympathy will do a great deal and convey pain
to any part, but there are no connections
between the sympathetic and optic nerves.
Here again we may remark the peculiar
sensibility of each part. You may pass
your finger over the eye-ball with little or no
inconvenience; but a grain of dust will
excite a copious flow of tears to wash it away.
There is no such thing as common
sensibility. The sensibility of the skin is one thing,
that of the eye another, that of the stomach
another. The cause of this difference we
know not: the reason of it is obvious, and
its perfection is a beautiful proof of that
wisdom which has fitted man so well for his
situation in the world. By it we are defended,
as by impregnable armour, from the thousand
external objects which would otherwise
assail us. Let the fifth nerve be paralysed—the
eye will see well enough by means of the optic
nerve, but it will no longer feel the particles of
dust upon its surface. They will collect, will
inflame, and will ultimately destroy the eye.
But supposing our knee or ancle joints were
sensitive to the same degree, we should be
unable to bear the mere weight of the body,
far less to walk. Yet were they not sensible
at all, we should want a guide to the amount
of pressure and of exertion they can bear
with impunity. If the skin of the hand were
not sensitive, we should take hold of red hot
irons like the poor soldier, and burn