Empedocles believes, that the joints of men begin to be formed from the thirty-sixth day, and their shape is completed in the nine and fortieth. Asclepiades, that male embryos, by reason of a greater natural heat, have their joints begun to be formed in the twenty-sixth day,--many even sooner,--and that they are completed in all their parts on the fiftieth day; the parts of the females are articulated in two months, but by the defect of heat are not consummated till the fourth; but the members of brutes are completed at various times, according to the commixture of the elements of which they consist. CHAPTER XXII. OF WHAT ELEMENTS EACH OF THE MEMBERS OF US MEN IS COMPOSED. Empedocles says, that the fleshy parts of us are constituted by the contemperation of the four elements in us; earth and fire mixed with a double proportion of water make nerves; but when it happens that the nerves are refrigerated where they come in contact with the air, then the nails are made; the bones are produced by two parts of water and the same of air, with four parts of fire and the same of earth, mixed together; sweat and tears flow from liquefaction of bodies. CHAPTER XXIII. WHAT ARE THE CAUSES OF SLEEP AND DEATH? 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 everything 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 relaxing 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 relaxing of the sensitive spirit, 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.