Man, like all the higher animals, is therefore subject to the law of lethality. But while animals have no idea of death and are not tormented by the sentiment of their inevitable end, man knows and understands this destiny. He has with the animals the instinct of self-preservation, the instinct of life, and at the same time the knowledge and the fear of death. This contradiction, this discordance, is one of the sources of his woes. Whether it be an accident or the regular term of the normal cycle, death always comes too soon. It surprises the man at a time when he has not yet completed his physiological evolution; hence the aversion and the terror it inspires. “We cannot fix our eyes on the sun or on death,” said La Rochefoucauld. The old man does not regard death with less aversion than the young man. “He who is most like the dead dies with most regret.” Man knows that he is not getting his full measure. Further, all the really natural acts are solicited by an instinct, the satisfaction of which is a need and a joy. The need of death should therefore appear at the end of life, just as the need of sleep appears at the end of the day. It would appear, no doubt, if the normal cycle of existence were fulfilled, and if the harmonious evolution were not always interrupted by accident. Death would then be welcomed and longed for. It would lose its horror. The instinct of death would replace at the wished for moment the instinct of life. Man would pass from the banquet of life with no other desire. He would die without regret, “being old and full of days,” according to the expression used in the Bible in the case of Abraham, Isaac, and Jacob. No doubt there are some analogies to this in the insects which only assume the perfect form for the purpose of procreation and immediately perish in their full perfection. In these animals the approach of death is blended with the intoxication of hymen. Thus we see some of them, the ephemerae, lose at that moment the instinct of life and the instinct of self-preservation. They allow themselves to be approached, taken, and seized, and make no effort at flight. But what is this full measure of life which is imparted to us? Metchnikoff holds that the ages attributed to several persons in the Bible are very probable. Abraham lived 175 years, Ishmael 137, Joseph 110, Moses 120. Buffon believed in the existence of a ratio between the longevity of animals and the duration of their growth. He fixed it at 7:1. The animal whose development lasts two years would thus have 14 years of life. This law would give us 140 years, but the figure is too high, and Flourens has reduced the ratio to that of 5:1, which would still give us 100 years. Plato died in the act of conversation at 81; Isocrates wrote his _Panathenaïcus_ at 94; Gorgias died in the full possession of his intellect at 107.