the
will, lest the passions or the indiscretions of the person should
continually avert those operations so necessary to health, and even to
life. The Divine Builder of this complicated machine has wisely
ordered that the muscles upon which these motions depend, shall act
under the impression of their proper stimulants, without the control
of the individual.

168. Again, there are certain operations which could not be safely
intrusted to the absolute government of the voluntary muscles, or
entirely removed from their control. Thus life can be supported only a
few minutes without breathing; but it would be impossible to perform
the daily vocations of life if we were compelled to breathe at all
times, or at perfectly regular intervals.

169. It has been observed that, among men of the same size, a wide
difference exists in their strength and activity--qualities which
depend upon the size and number of the nerves, the size and activity
of the brain, and the education, or training of the muscles. Men
having large nerves leading to the muscles, with the brain active,
and muscles well trained will perform feats of strength and agility,
that other men, of the same size, cannot effect. Rope-dancers,
harlequins, and other performers of feats, are persons thus
constituted.

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How many contractions and relaxations of the same muscle? What is said
of the rapidity of muscular contractions in other animals? 167. When
are the involuntary muscles called into action? Why would it not have
been safe to trust these important operations to the exclusive control
of the will? 168. Give an instance where some of the muscles act under
the government of the will, conjoined with those that are involuntary.
169. On what does the difference in muscular activity and strength
depend?

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170. Persons with small muscles, and largely developed nervous
systems, will sometimes exhibit very great muscular power for a time;
but it will not be of long continuance, unless the brain is
functionally diseased, as in hysteria, delirium of fever, insanity,
&c. Men of large muscles and small nerves can never perform feats of
great strength; but they have the power of endurance, and are better
capacitated for continued labor. Thus we cannot judge of the ability
of persons to make exertions and continue them, by their stature
alone. Strength, and the power of endurance, are the result of a
combination of