332 PHYSIOLOGY. 



4. /The organic or nutritial functions continue during 

 sleep, but with diminished energy.) The circulation and 

 respiration are not only slower, but digestion is retarded, 

 and secretion, nutrition, and calorification, are less active 

 than when awake. The temperature of the body is also 

 lowered during sleep, which may perhaps be owing to the 

 facts above mentioned. 



5. \!The duration of sleep is influenced by a variety of 

 circumstances^ (The average time of ^regular, periodical 

 sleep, in adults, is from five to eight hourjf. Infants require 

 twice as much sleep as grown persons. The- quantity of 

 sleep required,/depends very much upon habi$ It is said of 

 Pichegru, one of Buonaparte's generals, that, for a whole 

 year, he had not more than one hour of sleep in twenty-four 

 hours. Buonaparte himself, when on active duty, seldom 

 slept more than three hours in twenty-four ; often but one 

 hour. Men of active minds, who are engaged in a series 

 of interesting employments, sleep much less than the lazy 

 and the listless. The intellectual and moral faculties seem 

 to require a longer period of repose than the functions of 

 voluntary motion. 



6. Thoughfthe night is the proper season for sleep, owing 

 to the absence of light, diminished warmth, its comparative 

 stillness, as well as the exhaustion caused by the labours of 

 the day, yet some animals, which pursue their prey by night, 

 sleep during the day, as the cat, fox, wolf, otter, owl, and 

 bat. Hybernating animals sleep for several months during 

 the winter, such as the bear, hedge-hog, marmot, &c. Some 

 birds, also, such as bats and swallows, sleep during the win- 

 ter, or hybernate. During this state their temperature is di- 

 minished, their secretions nearly checked, their excretions 

 suppressed, their respiration slow, and scarcely perceptible, 

 their circulation very languid, and sensibility to external im- 

 pressions entirely suspended. The arterial blood of hyber- 

 nating animals, differs but little from venous blood. 



7. Dreams are now considered by physiologists to be 



