It remains, after having treated of everything connected with diet,
to say something of sleep, which is generally taken after every other
thing. Sleep, then, may be briefly defined to be a relaxation of the
vital powers, occasioned by a suitable moisture irrigating the brain.
When properly taken it may produce many good effects. It digests the
food, concocts the humours, soothes pain, alleviates lassitude, and
relaxes that which is contracted. It is also calculated to produce
oblivion of mental sufferings, and to rectify the distracted powers of
reason. The most suitable season for sleep is after a meal. But that
during the day does not agree with all, because the time spent in sleep
is not sufficient for the complete digestion of the food; and, when the
digestion is interrupted unseasonably, those who rise from sleep at noon
are often troubled with acidity and flatulence, and sometimes even with
a gurgling noise in their bowels, unless from habit or sufficient rest
these bad effects be obviated. The best season for sleep is the night,
for the humidity and drowsy stillness of night contribute to perfect
digestion. Wherefore after these nocturnal slumbers we feel the most
desire for evacuation. The proper limit to sleep should be the complete
digestion of the food, as may be ascertained by the eructations, and by
tapping over the stomach; after which it may be not unuseful to awake in
order to evacuate the excrementitious remains of the digestion.
* * * * *
COMMENTARY. The philosophy of sleep is ingeniously treated of by
Hippocrates (de Insomniis), and by Aristotle (in his treatise de Somno
et Vigilia.) Aristotle states that digestion goes on best during sleep.
Pliny’s definition of sleep seems to be taken from Hippocrates: “Est
autem somnus nihil aliud quam animi in medium sese recessus.” (H. N.
x, 97.) Alexander Aphrodisiensis, in like manner, says, “Know that,
during the day, the natural principle is less occupied with its own
peculiar operations, I mean the digestion of the food, the changes of
the chyle, sanguification, distribution, assimilation, and the like,
the mind being engaged in its other energies, namely, the five senses,
fantasy, reasoning, and memory; but during night, on the other hand,
nature operates more, and the mind less.” (Problem i, 118.) See also
particularly Oribasius (Med. Coll. vi, 4); Actuarius (de Diæta, 11);
Avicenna (i, 3, 3); Rhases (ad Mansor. iv, 3); Haly Abbas (Theor. v,
35); Alsaharavius (Theor. xi, 3); Averrhoes (Collect. i, 21.) Averrhoes
defines sleep to be the recession of the sensorial powers from their
organs to the internal parts; and hence, he remarks, those who sleep
with their eyes open do not perceive the objects nearest to them. The
vital heat being then collected internally, he adds, the powers of the
digestive faculty are increased. Rhases agrees with Galen that moderate
sleep forms good blood; but that too much corrupts the juices, that is to
say, impairs digestion. Haly Abbas remarks that, during sleep, the animal
powers are suspended, while the vital and natural continue unaffected;
and, therefore, the mind or principle of life being then disengaged, as
it were, from one of its offices, is the abler to perform the others
aright. Hence, he adds, digestion is best performed during sleep.
Alsaharavius approves of taking rest after a meal, but recommends an hour
to elapse before going to sleep.
The reader will find in Stentzel’s little treatise, entitled ‘Διατριβὴ
περι τοῦ ὕπνου,’ an interesting exposition of the opinions of the ancient
philosophers and physicians on this subject. There is an ingenious
disquisition on the nature of sleep in the commentary of Stephanus on
the Prognostics of Hippocrates. In reference to Aristotle’s division of
causes, he decides that the efficient cause of sleep is the rest of the
particular senses, and of the general sensorium: the material, a humidity
which is carried to the roots of the nerves, and prevents the exit of the
vital spirit; the formal or organic, the brain, in which the humidity is
collected; and the final, or end which sleep serves, the recreation of
the powers. (Dietz, T. i, 142.)