Volltext: Elements of Physiology

the nio-ht during summer, generally become quiet after midnight, especially when the 
pairing season is passed. Insects and spiders are frequently found in a lethargic or 
torpid°state; and it is probable that all animals in which no regular periods of sleep 
and waiting have hitherto been observed, have an equivalent for sleep in the state of 
inactivity and rest which they from time to time present. 
To return to man.—Persons in whom the organic functions predomi¬ 
nate, who are stout and full-blooded, sleep longer and require more 
sleep; and the contrary is the case with thin persons. Individuals of 
excitable, but at the same time energetic constitutions, and who are 
with difficulty fatigued, require less; those of an excitable, but more 
readily exhausted habit of body, require more sleep. In youth sleep 
is longer, and is more indispensably requisite, than in old age. This 
difference seems to depend on the greater predominance of the nutritive 
organic functions in youth. Hence the greater length of time passed in 
sleep by the new-born infant. This disposition to sleep is constant in 
the child as long as the organising action finds material in new nutritive 
matter supplied by food: and the child awakes when it requires nourish¬ 
ment. In the adult, also, abundant food induces sleepiness, partly by 
giving increased activity to the organic functions, and thereby disturbing 
the reaction of the animal functions, and partly by the pressure which 
the crude and imperfectly assimilated nutriment newly introduced into 
the blood exerts upon the brain. As causes favouring sleep, we must 
reckon also the impressions made on the sensorium by general stimu¬ 
lants of the skin, as friction of the surface, baths, &c., and the effects 
produced on the sensorium from within by sedative and narcotic medi¬ 


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