hers wait until motion has placed them in their proper situation, in suitable wombs or matrices, in the necessary circumstances, to unfold, to increase, to render them more perceptible by the addition of other substances of matter analogous to their primitive being. In all this we see nothing but the effect of motion, necessarily guided, modified, accelerated or slackened, strengthened or weakened, by reason of the various properties that beings successively acquire and lose; which, every moment, infallibly produces alterations in bodies more or less marked. Indeed, these bodies cannot be, strictly speaking, the same in any two successive moments of their existence; they must, every instant, either acquire or lose: in short, they are obliged to undergo continual variations in their essences, in their properties, in their energies, in their masses, in their qualities, in their mode of existence.
Animals, after they have been expanded in, and brought out of, the wombs that are suitable to the elements of their machine, enlarge, strengthen, acquire new properties, new energies, new faculties; either by deriving nourishment from plants analogous to their being, or by devouring other animals whose substance is suitable to their preservation; that is to say, to repair the continual deperdition or loss of some portion of their own substance, that is disengaging itself every instant. These same animals are nourished, preserved, strengthened, and enlarged, by the aid of air, water, earth, and fire. Deprived of air, or of the fluid that surrounds them, that presses on them, that penetrates them, that gives them their elasticity, they presently cease to live. Water, combined with this air, enters into their whole mechanism of which
