Life means change. We cannot imagine its continuance without liberation of energy. Arrest of molecular activity is death. There is no possibility of its revival. A watch that has stopped may be started by shaking. On the cessation of molecular activity an animate being becomes inanimate. Dead, it is liable to further chemical changes. Bacteria invade it. They shake down its complex unstable compounds into simple, stable, so-called “inorganic groups”; but the ordered combination with oxygen, which constitutes living, can never recommence. Putrefaction may be prevented by the exclusion of germs. The inanimate mass of organic material may remain unchanged. Its return to life would be a miracle. From time to time a frog is found enclosed in old red sandstone, or some other rock which for countless ages has lain beneath the surface. The cleft through which the frog entered a few hours or days before it was discovered is overlooked. It is supposed to have lived “in a state of suspended animation” for millions of years. The fact that no frogs are to be found among the fossils of the old red sandstone is an objection too casuistical to be seriously entertained. The physiologist’s demand to know what has become of the mountains of solid carbonic acid, water, and urea which the frog must have produced during its unimaginable term of incarceration is regarded as the natural expression of his prejudice—that life cannot continue without molecular change. And he is bound to admit his inability to prove that it cannot. Nevertheless, his experience that, whenever and however he may, by experimental methods, arrest change, he loses the power of causing it to recommence justifies him in his conviction that life is change. Even a living seed is to his mind an organism whose complex constituents are slowly—however slowly—setting free energy by settling down the steps which lead to stability and ultimate, inanimate rest; and the only source of this energy is combination with oxygen. In the case of a seed the oxygen need not come from without. Seeds retain their power of germination after long occlusion in nitrogen or other neutral gases. But all the time some change is occurring, some internal oxidation which resolves their less stable into more stable compounds. Otherwise they would not be alive. A physiologist is willing to believe that this may continue for ten years, fifteen years—for any period that the botanist tells him that he has, under verifiable conditions, observed that it does occur; but when he is told that peas taken from the hand of an Egyptian mummy, or seeds set free by the spades of navvies after a far longer burial, have been found to retain their vitality, his credulity is stretched beyond breaking-point. He cannot imagine a change so slow as to be spread over a geological period, still without exhaustion of all changeable compounds.