THE SLEEP‐WAKING CYCLE AND PUPILLARY ACTIVITY *

No sense organ is associated more closely with the rhythm of sleep and wakefulness than the eye, and for the majority of creatures the absence of visual stimulation, that is, darkness, elicits sleep. Conversely, no sense organ is affected as profoundly as the eye by wakefulness or by sleep. At least in the higher vertebrates, the eyes are closed and thus protected from stimulation during sleep. These facts are so ingrained in our consciousness that in common language, fatigue is described in terms of ocular signs: the eyes become heavy with sleep, lose their luster, and become increasingly smaller; the lids droop, and the pupils contract. Let us look a t these pupillary movements and examine their mechanism.