PLINY has compared a River to Human Life; and Sir Humphry Davy was a
hundred times struck with the analogy, particularly among mountain
scenery. A full and clear River is the most poetical object in nature;
and contemplating this, Davy wrote: “The river, small and clear in its
origin, gushes forth from rocks, falls into deep glens, and wantons and
meanders through a wild and picturesque country, nourishing only the
uncultivated tree or flower by its dew or spray. In this, its state of
infancy and youth, it may be compared to the human mind, in which fancy
and strength of imagination are predominant; it is more beautiful than
useful. When the different rills or torrents join, and descend into the
plain, it becomes slow and stately in its motions; it is applied to move
machinery, to irrigate meadows, and to bear upon its bosom the stately
barge;—in this mature state, it is deep, strong, and useful. As it flows
on towards the sea, it loses its force and its motion; and at last, as
it were, becomes lost and mingled with the mighty abyss of waters.”
Again, Life is often compared to a River, because one year follows
another, and vanishes like the ripples on its surface. A flood, without
ebb, bears us onward; “we can never cast anchor in the river of life,”
as Bernardin de St. Pierre finely and profoundly observes.
But the comparison can be still further developed. “It is taking a false
idea of life,” says Cuvier, “to consider it as a single link, which
binds the elements of the living body together, since, on the contrary,
it is a power which moves and sustains them unceasingly. These
elements,” he adds, “do not for an instant preserve the same relations
and connexions; or, in other words, the living body does not for an
instant keep the same state and composition.”
But this is only the new enunciation of a very old idea in science. Long
before Cuvier, Leibnitz said, “Our body is in a perpetual flux, like a
river; particles enter and leave it continually.” And long before
Leibnitz, physiologists had compared the human body to the famous ship
of Theseus, which was always the same ship, although, from having been
so often repaired, it had not a single piece with which it was
originally constructed. The truth is, that the idea of the continued
renovation of our organs[28] has always existed in science; but it is
also true that it has always been disputed.
M. Flourens has proved by direct experiment that the mechanism of the
development of the bones consists essentially in a continual irritation
of all the parts composing them. But it is the change of _material_; for
its _form_ changes very little. Cuvier has further developed this fine
idea:
In living bodies no molecule remains in its place; all enter and
leave it successively: life is a continued whirlpool, the direction
of which, complicated as it is, remains always constant, as well as
the species of molecules which are drawn into it, but not the
individual molecules themselves; on the contrary, the actual
material of the living body will soon be no longer in it; and yet it
is the depository of the force which will constrain the future
material in the same direction as itself. So that the form of these
bodies is more essential to them than the material, since this
latter changes unceasingly, while the other is maintained.
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Footnote 28:
One may well say of a given individual, that he lives and is the same,
and is spoken of as an identical being from his earliest infancy to
old age, without reflecting that he does not contain the same
particles, which are produced and renewed unceasingly, and die also in
the old state, in the hair and in the flesh, in the bone and in the
blood,—in a word, in the whole body.—_Plato; The Banquet._
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