Alcmaeon says, that sleep is caused when the blood retreats to the concourse of the veins, but when the blood diffuses itself, then we awake; and when there is a total retirement of the blood, then men die. Empedocles, that a moderate cooling of the blood causeth sleep, but a total remotion of heat from blood causeth death. Diogenes, that when all the blood is so diffused as that it fills all the veins, and forces the air contained in them to the back and to the belly that is below it, the breast being thereby more heated, thence sleep arises; but if every thing that is airy in the breast forsakes the veins, then death succeeds. Plato and the Stoics, that sleep ariseth from the relaxation of the sensitive spirit, it not receiving such total remission as if it fell to the earth, but so that that spirit is carried about the intestine parts of the eyebrows, in which the principal part has its residence; but when there is a total remission of the sensitive spirit, then death ensues. CHAPTER XXIV. WHEN AND FROM WHENCE THE PERFECTION OF A MAN COMMENCES. Heraclitus and the Stoics say, that men begin their completeness when the second septenary of years begins, about which time the seminal serum is emitted. Trees first begin their perfection when they give their seeds; till then they are immature, imperfect, and unfruitful. After the same manner a man is completed in the second septenary of years, and is capable of learning what is good and evil, and of discipline therein. CHAPTER XXV. WHETHER SLEEP OR DEATH APPERTAINS TO THE SOUL OR BODY. Aristotle’s opinion is, that both the soul and body sleep; and this proceeds from the moisture in the breast, which doth steam and arise in the manner of a vapor into the head, and from the aliment in the stomach, whose natural heat is cooled in the heart. Death is the perfect refrigeration of all heat in the body; but death is only of the body, and not of the soul, for the soul is immortal. Anaxagoras thinks, that sleep makes the operations of the body to cease; it is a corporeal passion and affects not the soul. Death is the separation of the soul from the body. Leucippus, that sleep is only of the body; but when the smaller particles cause immoderate evaporation from the soul’s heat, this makes death; but these affections of death and sleep are of the body, not of the soul. Empedocles, that death is nothing else but separation of those fiery parts by which man is composed, and according to this sentiment both body and soul die; but sleep is only a smaller separation of the fiery qualities. CHAPTER XXVI. HOW PLANTS GROW, AND WHETHER THEY ARE ANIMALS.