CHAPTER XYI. 



SLEEP. 



General considerations Condition of the organism during sleep Dreams Re- 

 flex mental phenomena during sleep Condition of the brain and nervous 

 system during sleep Theories of sleep Anaesthesia and sleep produced 

 by pressure upon the carotid arteries Differences between natural sleep, 

 and stupor and coma Regeneration of the brain-substance during sleep 

 Theory that sleep is due to a want of oxygen Condition of the various func- 

 tions of the organism during sleep. 



we remember that about one-third of our existence 

 is passed in sleep, and thai, at this time, voluntary motion, 

 sensation, the special senses, and various of the functions of 

 the organism, are greatly modified, the importance of a physi- 

 ological study of this condition is sufficiently apparent. The 

 subject of sleep is most appropriately considered in connec- 

 tion with the nervous system, for the reason that the most 

 important modifications in function are observed in the 

 cerebro-spinal axis and nerves. Hepose is as necessary to 

 the nutrition of the muscular system as proper exercise ; but 

 repose of the muscles relieves the fatigue due to exercise, 

 without sleep. It is true that after violent and prolonged 

 exertion, there is frequently a desire for sleep, but simple 

 repose will often restore the muscular power. After the 

 most violent effort, a renewal of muscular vigor is most easily 

 and completely effecte'd by rest without sleep, a fact familiar 

 to all who are accustomed to athletic exercises. The glands 

 engaged in the production of the true secretions need certain 

 Intervals of repose ; but this does not necessarily involve 



