On Sleep And Sleeplessness   

without intermission; for all organs which have a natural function

must lose power when they work beyond the natural time-limit of

their working period; for instance, the eyes [must lose power] from

[too long continued] seeing, and must give it up; and so it is with

the hand and every other member which has a function. Now, if

sense-perception is the function of a special organ, this also, if

it continues perceiving beyond the appointed time-limit of its

continuous working period, will lose its power, and will do its work

no longer. Accordingly, if the waking period is determined by this

fact, that in it sense-perception is free; if in the case of some

contraries one of the two must be present, while in the case of others

this is not necessary; if waking is the contrary of sleeping, and

one of these two must be present to every animal: it must follow

that the state of sleeping is necessary. Finally, if such affection is

Sleep, and this is a state of powerlessness arising from excess of

waking, and excess of waking is in its origin sometimes morbid,

sometimes not, so that the powerlessness or dissolution of activity

will be so or not; it is inevitable that every creature which wakes

must also be capable of sleeping, since it is impossible that it

should continue actualizing its powers perpetually.

So, also, it is impossible for any animal to continue always

sleeping. For sleep is an affection of the organ of

sense-perception--a sort of tie or inhibition of function imposed on

it, so that every creature that sleeps must needs have the organ of

sense-perception. Now, that alone which is capable of sense-perception

in actuality has the faculty of sense-perception; but to realize

this faculty, in the proper and unqualified sense, is impossible while

one is asleep. All sleep, therefore, must be susceptible of awakening.

Accordingly, almost all other animals are clearly observed to

partake in sleep, whether they are aquatic, aerial, or terrestrial,

since fishes of all kinds, and molluscs, as well as all others which

have eyes, have been seen sleeping. 'Hard-eyed' creatures and