CHAPTER XI 



SLEEP 



Sleep is not only necessary to rest a tired mind and 

 body, but more essential to life than food itself. Com- 

 plete fasting has extended over periods measured by 

 weeks, but total absence of sleep for four or five days 

 is likely to end fatally. The imperative nature of the 

 demand for sleep is shown in the thousands of cases in 

 which soldiers have slept on horseback, while marching 

 and even when on sentry duty, when the penalty is 

 death. Notwithstanding the universality of this phys- 

 iologic function, we are almost entirely in the dark as 

 to its mechanism, a fact sufficiently proved by the 

 number of theories advanced and the contradictory 

 nature of the evidence adduced in their support. Some 

 of the changes which occur during sleep are established 

 and may be accepted as proved. 



Not only is night, when many forms of work must 

 cease for want of light, the time during which most 

 people sleep, but there seems little reason to doubt the 

 statement that night sleep is more restful than that 

 during daylight. "Daylight sleep, in fact, is less re- 

 cuperative and less profound and unbroken than night 

 sleep." (Luciani). Sleep is usually preceded by drowsi- 

 ness, indicated by a pricking sensation in the eyes, 

 drooping of the upper lid, probably from fatigue of the 

 muscle which supports it, dulling of the mind ana in- 

 ability to fix the attention. Usually we compose our- 

 selves, the drowsiness deepens until we lose all idea of 



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