THE PHYSIOLOGY OF SLEEP. 411 



THE PHYSIOLOGY OF SLEEP. 



By B. W. RICHAEDSON, M. D., F. E. S. 



rpHE twinkling of oblivion," as Wordsworth exquisitely defines 

 JL the phenomenon of sleep, has, from the time of Hippocrates to 

 the present hour, engaged the attention of thoughtful minds. Poets 

 have found in the phenomenon subject-matter for some of the most 

 perfect of their works. Menander exalts sleep as the remedy for every 

 disease that admits of cure ; Shakespeare defines it, " The birth of each 

 day's life, sore labor's bath;" Sir Philip Sidney designates it, " The 

 poor man's wealth, the prisoner's release ; " and wearied Dryden sings 



of it 



" Of all the powers the best. 



Oh ! peace of mind, repairer of decay, 



Whose balms renew the limbs to labors of the day." 



As to the philosophers and the physicians who have said and writ- 

 ten on sleep, I dare hardly think of them, lest I should commit myself 

 to an historical volume instead of a short physiological essay ; so I 

 leave them, except such as are simply physiological, and proceed on 

 my way. 



Perfect sleep is the possession, as a rule, of childhood only. The 

 healthy child, worn out with its day of active life, suddenly sinks to 

 rest, sleeps its ten or twelve hours, and wakes, believing, feeling, that 

 it has merely closed its eyes and opened them again ; so deep is its 

 twinkle of oblivion. The sleep in this case is the nearest of approaches 

 to actual death, and at the same time presents a natural paradox, for 

 it is the evidence of strongest life. 



During this condition of perfect sleep, what are the physiological 

 conditions of the sleeper ? Firstly, all the senses are shut up, yet are 

 they so lightly sealed that the communication of motion by sound, by 

 mechanical vibration, by communication of painful impression, is suffi- 

 cient to unseal the senses, to arouse the body, to renew all the proofs 

 of existing active life. Secondly, during this period of natural sleep 

 the most important changes of nutrition are in progress ; the body is 

 renovating, and, if young, is actually growing ; if the body be properly 

 covered, the animal heat is being conserved and laid up for expenditure 

 during the waking hours that are to follow ; the respiration is reduced, 

 the inspirations being lessened in the proportion of six to seven as 

 compared with the number made when the body is awake ; the action 

 of the heart is reduced ; the voluntary muscles, relieved of all fatigue 

 and with the extensors more relaxed than the flexors, are undergoing 

 repair of structure and recruiting their excitability ; and the voluntary 

 nervous system, dead for the time to the external vibration, or as the 



