What was life? No one knew. No one knew the actual point whence it sprang, where it kindled itself. Nothing in the domain of life seemed uncausated, or insufficiently causated, from that point on; but life itself seemed without antecedent. If there was anything that might be said about it, it was this: it must be so highly developed, structurally, that nothing even distantly related to it was present in the inorganic world. Between the protean amoeba and the vertebrate the difference was slight, unessential, as compared to that between the simplest living organism and that nature which did not even deserve to be called dead, because it was inorganic. For death was only the logical negation of life; but between life and inanimate nature yawned a gulf which research strove in vain to bridge. They tried to close it with hypotheses, which it swallowed down without becoming any the less deep or broad. Seeking for a connecting link, they had condescended to the preposterous assumption of structureless living matter, unorganized organisms, which darted together of themselves in the albumen solution, like crystals in the mother-liquor; yet organic differentiation still remained at once condition and expression of all life.