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is to learn to sleep whenever you wish to. You never know how 
useful it may be. The effect of meals upon sleep, he pointed 
out, is well known. ‘This is aptly seen in animals, who have no 
business to keep them awake. Here the Doctor paused to pro- 
test against the bad habit of taking the heaviest meal of the day 
four hours before sleep, which comes at the time when the body 
is becoming energised by the food. Touching upon the patho- 
logical phenomena of sleep, Dr. Griffith dealt with the causes of 
sleeplessness. The sleep of the labouring man is sound, whether 
he eat much or little: often not all the abundance of the rich 
will suffer them to sleep. A moderate amount of work, bodily 
or mental, will produce good sleep, but excess of either will pre- 
vent it. Too much mental work, for instance, even if it has not 
reached the stage when black coffee or a wet towel round one’s 
head is necessary, will cause a restless night. Anxiety, the 
stimulation of the blood caused by pain, and an excess of 
physical work, especially of a bustling nature, will act in the same 
way. The occupation of the mind with one fixed idea is a sure 
preventive of sleep,—-a thing strikingly noticeable in the insane. 
Turning to the causes that induce sleep, Dr. Griffith said that 
these affect the circulation of the blood, or they diminish sensation. 
Most prominent are various drugs, such as opium, Indian hemp, 
chloral, bromides, etc., which act partly on the brain and partly 
on the nerves of sensation. After taking Indian hemp a person 
imagined himself propelled through eternity and in his flight he 
saw an elephant magnified to hundreds and thousands of times its 
natural size. Even beer, added the Doctor slyly, had been known 
to produce a very drowsy state in some people. A stuffy 
atmosphere would also induce sleep. The familiar effect of sleep 
in church is less the result of the sermon than the want 
of ventilation. Dr. Griffith thought it would be interest- 
ing to try the effect of more ventilation in some of our 
churches as a means of preventing sleep. There are three main 
ideas, said the Doctor, as to the explanation of the physiological 
condition of sleep. One idea is that sleep is simply an illustration 
of the great natural law of rhythm. All earthly things alternate, 
or are balanced. ‘Thus there are two great forces,—one, gravita- 
tion, drawing the earth to the sun; the other, centrifugal force, 
keeping it to its orbit. Fits and fidgets have their still moments ; 
whooping-cough has its periods of quiet ; and even Conservative 
Governments cease at times. This humorous parallel was much 
relished by the audience, and helped them to appreciate the 
lecturer's point that, in accordance with the natural law of rhythm, 
sleep must come at some time or other. A second theory of the 
causes of sleep is that it depends on changes in the circulation of 
the blood, and the consequent effect on the brain, the actual 
condition during sleep being one of brain bloodlessness. There is 
