off
what has already been taken. Loss of appetite in sickness is thus a
kind provision of nature, to prevent our taking food when it would be
injurious; and following this intimation, we, as a general rule,
should abstain from food until the appetite returns.

[Illustration: Fig. 133. A back view of the brain and spinal cord. 1, The
cerebrum. 2, The cerebellum. 3, The spinal cord. 4, Nerves of the face.
5, The brachial plexus of nerves. 6, 7, 8, 9, Nerves of the arm. 10,
Nerves that pass under the ribs, 11, The lumbar plexus of nerves. 12, The
sacral plexus of nerves 13, 14, 15, 16, Nerves of the lower limbs.]

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What is the function of this nerve? What is the effect if the seventh
pair is divided, or its function destroyed by disease? 791. What is
said of the sympathetic nerve? 792. What is the use of the sympathetic
system? Explain fig. 133.

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_Note._ Let the anatomy and physiology of the nervous system be
reviewed from figs. 131, 132, 133, or from anatomical outline plate.
No. 8.

CHAPTER XXXIX.

HYGIENE OF THE NERVOUS SYSTEM.

793. As the different organs of the system are dependent on the brain
and spinal cord for efficient functional action, and as the mind and
brain are closely associated during life, the former acting in strict
obedience to the laws which regulate the latter, it becomes an object
of primary importance in education, to discover what these laws are,
that we may escape the numerous evils consequent on their violation.

794. _For healthy and efficient action, the brain should be primarily
sound_; as this organ is subject to the same general laws as other
parts of the body. If the brain of the child is free from defects at
birth, and acquires no improper impressions in infancy, it will not
easily become diseased in after life. But, if the brain has inherited
defects, or has acquired a proneness to disease by mismanagement in
early life, it will more easily yield to influences that cause
diseased action. The hereditary tendency to disease is one of the most
powerful causes that produce nervous and mental affections.
Consequently, children have a strong tendency to the diseases from
which the parents suffered.

795. When both parents have similar defects, or have descended from
tainted families, the children are usually more deeply impressed with
their imperfections than when only one possesses the defect. This is
the reason of