CHAPTER LXXIV 

 SLEEP 



SLEEP is to be regarded as the period of rest of the great brain, 

 and to a certain extent of the central nervous system and of the body 

 generally. It is probable that absolute lack of sleep would kill a 

 man even more speedily than absolute lack of water, and certainly 

 more quickly and painfully than the withdrawal of food. Young 

 puppies three to four months old, deprived of sleep for four to five 

 days, died either at once or, if then allowed to sleep, after a few 

 days. The younger the animal, the more speedy its death. The 

 body temperature began to fall on the second day, until just before 

 death the temperature was about 5 C. below normal. The number 

 of blood-corpuscles became greatly diminished, and after death many 

 capillary haemorrhages were found in the brain. 



It is probable that the greater the animal's need of sleep, the 

 quicker its death from sleeplessness. Dogs sleep, probably, on an 

 average twice as long as man, who normally sleeps about one-third of 

 his life. Some men require considerably less sleep than others ; why, 

 it is difficult to say. Children require, according to age, from twelve 

 to ten hours' sleep, women and men from eight to five hours'. Birds 

 apparently require less sleep than mammals. Some mammals require 

 considerably more sleep than others. This is partly due to the character 

 of the sleep, a short profound sleep being as efficacious as a longer less 

 deep sleep. Man is a deep sleeper; the dog is a light sleeper. The 

 companionship of the dog has helped man to attain to his supremacy. 

 But for the companionship and guardianship of the light sleeper, the 

 deep sleeper would have been destroyed by night-prowling, man- 

 eating enemies. 



Many observations have been made upon man to determine the 

 physiological conditions during sleep. Most marked is the loss of 

 consciousness. It is stated that sleep is more profound in the half 

 of the brain which has been active during the day, so that right- 

 handed people when asleep flick away a fly with the left hand, while 

 true left-handed people perform such an act with the right hand. 

 The depth of the loss of consciousness may be gauged by stimuli, 

 such ds the ringing of a bell at half-hour intervals during the sleep, 

 the dropping of a lead ball from a given height on to a lead plate, 

 or the application of electrical stimuli of known intensity. By such 

 means it has been determined that the greatest intensity of sleep 

 occurs after about an hour to an hour and a half from the onset of 



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