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ON SLEEP. 
By Dr. RICHARDSON, F.R.S. 
The Phenomenon of Sleep. 
66 rjlHE twinkling of oblivion,” as Wordsworth exquisitely 
X defines 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, 66 The birth of each 
day’s life, sore labour’s bath ; ” Sir Philip Sydney 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 halms renew the limbs to labours of the day.” 
As to the philosophers and the physicians who have said 
and written 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, sud- 
denly 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 physio- 
logical 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 communica- 
tion of painful impression, is sufficient 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 impor- 
