This moisture, or humor,—ought to be warm, he writes; when it is cold, sleep will not be produced,—just as those affected with sleepiness show that their systems are in warm and at the same time humid condition; and children, who have abundance of this warm moisture, sleep the most; whence he states that this sleep chill has in fact its causes at the outset in this very warmth. These things he discusses partly in the book on “Sleep and Waking,” partly in the second of “The Parts of Animals,” and in “Problems.” I am not able to judge concerning the first matter, the idea of giving a single cause of sleep. For, according to this author, waking brings sleep;[12] since even animals, by means of waking and exercising their functions are known to become quiet and sleep, and it is said by him, that since animals become helpless in sleep, this helplessness is produced by the excess of waking that precedes it. [12] It appears that Argenterio thinks Aristotle inconsistent in his proposition here. But not in waking, in food, or in this reason of generated vapor, is it possible to place the cause of sleep. Exercise produces this very effect. For through labor, deep and sweetest sleep falls upon the creatures; and this not on account of vapors rising from food, nor on account of a natural moisture, so much as by the violent exercise of the body. Foods that are cold or dried, as the hull of the mandrake,—taken into the body, induce sleep; which therefore is not accomplished because these foods give rise to vapors, since they would rather banish the vapors by their dryness; nor would these foods supply to the head what vapor is generated, since, repelled by the cold of such substances being taken into the body, the moisture would be repelled and chilled, and prevent the vapor from being carried to the brain. This would be so, as he says, only if the generation of vapors, and their ascent arose from the heating of this natural humor or moisture. * * * * * Other chapters of interest in Argenterio’s “Sleep and Waking” are: CHAPTER II: What may bring sleep, and by what method, according to Galen. CHAPTER III: The causes producing sleep, which are thought true. CHAPTER XI: In what way sleep may be produced from natural heat. CHAPTER XIII: Concerning natural causes of Sleep and Waking. CHAPTER XIV: Concerning unnatural causes of Sleep and Waking. CHAPTER XVII: Of causes of long and short sleep. APPENDIX D QUESTIONNAIRE ON SLEEP In order to get the facts about SLEEP we sent a question sheet to a large number of persons selected by classes. We began with a thousand professors in order to get suggestions which might make the investigation more useful. The following request was sent out: PLEASE FILL OUT AND RETURN—