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. --------------------- 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._ ---------------------------- THE SPRING-TIME OF LIFE.