Accordingly [in sleep] the upper and outward parts are cool, but the

inward and lower, i.e. the parts at the feet and in the interior of

the body, are hot.

Yet one might found a difficulty on the facts that sleep is most

oppressive in its onset after meals, and that wine, and other such

things, though they possess heating properties, are productive of

sleep, for it is not probable that sleep should be a process of

cooling while the things that cause sleeping are themselves hot. Is

the explanation of this, then, to be found in the fact that, as the

stomach when empty is hot, while replenishment cools it by the

movement it occasions, so the passages and tracts in the head are

cooled as the 'evaporation' ascends thither? Or, as those who have hot

water poured on them feel a sudden shiver of cold, just so in the case

before us, may it be that, when the hot substance ascends, the cold

rallying to meet it cools [the aforesaid parts] deprives their

native heat of all its power, and compels it to retire? Moreover, when

much food is taken, which [i.e. the nutrient evaporation from which]

the hot substance carries upwards, this latter, like a fire when fresh

logs are laid upon it, is itself cooled, until the food has been

digested.

For, as has been observed elsewhere, sleep comes on when the

corporeal element [in the 'evaporation'] conveyed upwards by the

hot, along the veins, to the head. But when that which has been thus

carried up can no longer ascend, but is too great in quantity [to do

so], it forces the hot back again and flows downwards. Hence it is

that men sink down [as they do in sleep] when the heat which tends

to keep them erect (man alone, among animals, being naturally erect)

is withdrawn; and this, when it befalls them, causes

unconsciousness, and afterwards phantasy.

Or are the solutions thus proposed barely conceivable accounts of

the refrigeration which takes place, while, as a matter of fact, the

region of the brain is, as stated elsewhere, the main determinant of