Book 5
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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 the nerves; but when it happens that the nerves are refrigerated where they meet 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, duly mixed together; sweat and tears flow from the liquefaction of these bodies of ours.
Chapter XXIII. WHAT ARE THE CAUSES OF SLEEP AND DEATH?
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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.
