would be that the impression had been conveyed
to the brain, and from the brain to the heart by the pneumogastric nerves.
The result would be that the heart for an instant ceases to beat. Death
would be the result if the nerve influence were so great as to restrain
the movements of the heart for any appreciable time.

Again, if the person were the subject of some emotion by which the heart
were beating faster than usual, it would mean that there was sent from the
brain to the heart by the sympathetic nerves the impression which
stimulated it to increased activity.

195. The Nervous Control of the Blood-vessels. The tone and caliber
of the blood-vessels are controlled by certain vaso-motor nerves,
which are distributed among the muscular fibers of the walls. These nerves
are governed from a center in the medulla oblongata, a part of the brain
(sec. 270). If the nerves are stimulated more than usual, the muscular
walls contract, and the quantity of the blood flowing through them and the
supply to the part are diminished. Again, if the stimulus is less than
usual, the vessels dilate, and the supply to the part is increased.

Now the vaso-motor center may be excited to increased activity by
influences reaching it from various parts of the body, or even from the
brain itself. As a result, the nerves are stimulated, and the vessels
contract. Again, the normal influence of the vaso-motor center may be
suspended for a time by what is known as the inhibitory or
restraining effect. The result is that the tone of the blood-vessels
becomes diminished, and their channels widen.

The effect of this power of the nervous system is to give it a certain
control over the circulation in particular parts. Thus, though the force
of the heart and the general average blood-pressure remain the same, the
state of the circulation may be very different in different parts of the
body. The importance of this local control over the circulation is of the
utmost significance. Thus an organ at work needs to be more richly
supplied with blood than when at rest. For example, when the salivary
glands need to secrete saliva, and the stomach to pour out gastric juice,
the arteries that supply these organs are dilated, and so the parts are
flushed with an extra supply of blood, and thus are aroused to greater
activity.

Again, the ordinary supply of blood to a part may be lessened, so that the
organ is reduced to a state of inactivity, as occurs in the c