ich will be indicated by a sense of weariness in these
parts. A change of employment and position calls into action a
different set of muscles, and the exhausted organs are relieved.

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177. What is said of the contraction and relaxation of the muscles?
Give examples of the necessity of relaxing the muscles. 178. Why
should not small children be confined in one position for a long time?
What evils result from this practice? What class of pupils should have
recesses most frequently? 179. What effect has continued muscular
contraction?

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180. _Much more labor will be accomplished by taking time to relax the
exhausted muscles_, or by so changing the employment as to bring into
action a new set of muscles; the woodman thus relieves himself, by
sawing and splitting alternately. This principle applies to the labor
of the horse and ox; and it is also applicable to all kinds of
employment. With the invalid convalescing from fever, relapses result
from inattention to these laws. When a patient is recovering from
sickness, his physician should take care that his exercise be proper,
neither too much, too little, nor too long continued.

181. _The muscles of growing youths will not endure so much exercise
or labor as those of mature men._ In youth a portion of the vital, or
nervous energy of the system, is expended upon the growth of the
organs of the body, while in the individual who has attained his
growth, this expenditure is not demanded; consequently severe labor or
exercise should not be imposed on growing children.

_Observation._ In the campaigns of Napoleon Bonaparte, his army was
frequently recruited by mere boys. He complained to the French
government, because he was not supplied with men of mature years, as
the youths could not endure the exertion of his forced marches.

182. _The muscles should be gradually called into action._ These
organs in action require more blood and nervous fluid than when at
rest. As the circulation of these fluids can only be increased in a
gradual manner, it follows, that, when the muscular system has been in
a state of rest, it should not suddenly be called into vigorous
action. On arising from a bed, lounge, or chair, the first movements
of the limbs should be slow, and then gradually increased.

_Observation._ if a man has a certain amount of work to perform in
nine hours, and his muscles have been in a state of rest, he will do