several conditions, if we may be permitted to employ a figurative
expression. Were there no such medium, how would the stomach notify
the heart that additional exertion on its part is required, because
the stomach is busy in digesting food?

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725. What has been noted in the preceding chapters? 726. Show the
manner in which the several processes are performed. 727. How must
they succeed each other?

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728. "When we are exerting the muscular system for a long time in some
laborious employment, how else are our members to inform the stomach
that they are too much occupied with their duties to spare the blood
necessary in digestion; that it is requisite that the appetite
should decline; and that digestion should cease for the time, even if
the stomach should be oppressed with its contents? When we are
thinking, how else are the blood-vessels to be told that an unusual
supply of their contents is wanting in the head? or when the whole
frame is weary with exertion, how, without some regular line of
intelligence between all the organs, is the brain to be instructed
that circumstances require that it should go to sleep? To supply the
necessary medium of communication, Providence has furnished all the
animals that possess distinct organs, with a peculiar apparatus
called the _Nervous System_."

ANATOMY OF THE NERVOUS SYSTEM.

729. The NERVOUS SYSTEM consists of the _Cer'e-bro-spi'nal Cen'tre_,
and of numerous rounded and flattened white cords, called _nerves_,
which are connected at one extremity with the cerebro-spinal centre,
and at the other, distributed to all the textures of the body. The
sympathetic nerve is an exception to this description; for, instead of
one, it has many small centres, which are called _gan'gli-a_, and
which communicate very freely with the cerebro-spinal centre, and with
its nerves.

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728. What is the medium of communication from one organ to another?
729-754. _Give the anatomy of the brain and cranial nerves._ 729. Of
what does the nervous system consist? What constitutes an exception to
this?

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730. The CEREBRO-SPINAL CENTRE consists of two portions: The _brain_,
and the _spinal cord_. For convenience of description, the nervous
system may be divided into the _Brain_, _Cranial Nerves_, _Spinal
Cord_, _Spinal Nerves_, and the _Sympathetic Nerve_.

731. The term BRAIN designates