nce from food.

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438-454. _What remarks respecting nutrition?_ 438. What is nutrition?
439. What is said of the nutritive process? The function of the
nutrient vessels? 440. Give a proof of the ever-changing state of the
body. Give other instances illustrative of the changeful state of the
body.

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441. Every part of the body is subject to this continual change of
material, yet it is effected with such regularity, that the size,
shape, and appearance, of every organ is preserved; and after an
interval of a few years, there may not remain a particle of matter
which existed in the system at a former period. Notwithstanding this
entire change, the personal identity is never lost.

442. Many calculations have been made to determine in what length of
time the whole body is renewed. Some have supposed that it is
accomplished in four years; others have fixed the period at seven
years; but the time of the change is not definite, as was supposed by
a genuine son of the Emerald Isle, who had been in America _seven
years and three months_, and consequently maintained that he was a
native American.

_Observation._ India ink, when introduced into the skin, is not
removed; hence some assert that this tissue is an exception to the
alternate deposition and removal of its atoms. The ink remains because
its particles are too large to be absorbed, and when in the skin it is
insoluble.

443. "Those animals which are most complicated in their structure, and
are distinguished by the greatest variety of vital manifestations, are
subject to the most rapid changes of matter. Such animals require more
frequent and more abundant supplies of food; and, in proportion as
they are exposed to the greater number of external impressions, will
be the rapidity of this change of matter."

444. "Animals may be situated so that they lose nothing by secretion;
consequently, they will require no nutriment. Frogs have been taken
from fissures in solid lime rock, which were imbedded many feet below
the surface of the earth, and, on being exposed to the air, exhibited
signs of life."

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441. Why is the personal identity never lost in the change of
materials, which is unceasing in the system? 442. Give the opinion of
physiologists respecting the time required for the renewal of the
whole body. What exception to the changing state Of the different
textures? 443. What anima