4i o POPULAR SCIENCE MONTHLY. 



too, for long periods. Some sleep lightly, retaining in greater part 

 their consciousness. Occasionally we hear of an individual who has 

 lived for a long time without sleep, so far as can be determined, and 

 yet has continued to maintain good health. Sufferers from one form 

 or another of nervous exhaustion are often compelled to forego sleep 

 temporarily. Vigorous persons of pronounced personality and highly 

 developed consciousness have the least need for sleep, at least while 

 at the zenith of their powers and in the full flower of energizing. 



The maintenance of conscious life demands an expenditure of 

 energy so intense that the processes of nutrition and reconstruction 

 of cellular waste can not be carried on without sleep. Complete 

 repose of the consciousness is demanded for the plastic nutrition of 

 the organism and the accomplishment of vegetative life. Consciousness 

 is the highest of our faculties, rendering possible moral and scientific 

 ideation; it demands the greatest efforts of our organism. In its 

 absence sleep is less required. 



All the internal organs are, during sleep, relatively less filled with 

 blood because then the skin is in a state of hyperemia or gorged with 

 blood. The sweat glands act more energetically at night whether we 

 are asleep or awake, hence the danger of chills is then greater. All 

 the organic activities continue, but are less vigorous at night, and 

 during sleep, whereas during sleep in daylight hours these proceed with 

 little alteration. When animals or men feel the desire to sleep they 

 instinctively seek a quiet sheltered spot, as free as possible from light 

 and noise, thus avoiding whatever impressions from the external world 

 are liable to be subjectively translated into sensations. The eyelids are 

 lowered; a position is sought wherein the muscles can be fully relaxed. 

 The sensorial organs are capable of acting during sleep and continue 

 to transmit impressions into conscious sensations. 



With the pallor of the brain, which occurs in sleeping animals, 

 the cortex ceases to react so readily to mechanical, photic, electric or 

 other stimuli. The spinal cord and sensory nerves do not sleep, yet 

 sensations of pain are then lowered. The nerves transmit painful 

 impressions, but the consciousness of the sleeper perceives them incom- 

 pletely. The voluntary muscles become quiescent during sleep, but 

 retain their power, as shown by the normal subject in changing posi- 

 tion, arranging the bedclothes, even walking; soldiers are able to 

 march or ride while asleep. The brain is the chief part which sleeps, 

 but it is not wholly inactive, exciting inhibitions which check the forma- 

 tion of reflex movements. If stimuli are applied of sufficient intensity 

 to overcome the protective states of the somnolent consciousness the 

 subject awakes, recognizing the cause more or less certainly. 



Sleep is not an absolute arrest of cerebral activity; the brain then 

 retains always partial energy. In deprivation of sleep it is the brain 



