310 



capacity of continuing, for a certain time, in a state of equal activity; for 

 it is easy to see how imperfect, relations interrupted at every moment, 

 would have been: their reposej which constitutes sleep, is of equal dura- 

 tion. 



The duration of sleep is from a fourth to a third of the day: few sleep 

 less than six hours, or more than eight. Children, however, require 

 longer sleep; the more, the nearer they are to the period of their birth. 

 Old men, on the contrary, have short sleep, light, and broken; as if, says 

 Grimaud, according to Stahl's notions, children foresaw that in the long 

 career before them, there were time enough for performing, at leisure, 

 all the acts of life, while old men near to their end, felt the necessity of 

 hurrying the enjoyment of a good already about to escape. 



If the sleep of a child is long, and deep, and still, it is the wonderful 

 activity of the assimilating functions that makes it so, and perhaps the 

 habit itself of sleep, in which he has passed the first nine months of his 

 life, or all the time before his birth. In advanced age, the internal func- 

 tions grow languid; their organs no longer engage the action of the prin- 

 ciple of life; and the brain is moreover so crowded with ideas, that it is 

 almost always kept awake by them. Carnivorous animals sleep longer 

 than graminivorous, because during waking they are more in motion, 

 and perhaps, too, because the animal substances on which they subsist, 

 yielding them more nutritious particles, from the same bulk, they have 

 need of less time for devouring their food and providing for their sub- 

 sistence*. 



Sleep is a state essentially different from death, to which some authors 

 have erroneously likened itf. It merely suspends that portion of life> 

 which serves to keep up with outward objects an intercourse necessary 

 to our existence. One may say, that sleep and waking call each other, 

 and are of mutual necessity. The organs of sense and motion, weary of 

 acting, rest ; but there are many circumstances favouring this cessation 

 of their activity. A continual excitation of the organs of sense would 

 keep them continually awake; the removal of the material causes of our 

 sensations tends, therefore, to plunge us into the arms of sleep: where- 

 fore we indulge in it more voluptuously in the gloom and the stillness of 

 nightj:. Our organs fall asleep one after the other; the smell, the taste, 

 and the sight are already at rest, when tke hearing and the touch still 

 send up faint impressions. The perceptions, awhile confused, in the end 

 disappear; the internal senses cease acting; as well as the muscles al- 

 lotted to voluntary motion, whose action is entirely subject to that of the 

 brain. 



* Probably, their more powerful digestion of a more nutritious food, bringing into 

 the system a more sudden accession of blood, oppresses them with sleep : a sleep and 

 a fullness of blood required to recruit the powers that have been exhausted by the la- 

 borious quest of food, and by the long continued endurance of hunger. 



Animal food, according to the extent to which it is indulged in, or the length of the 

 intervals between its use, produces either absolute or relative vascular plethora, both 

 which states dispose to sleep. 



}- To say that sleep is the image of death, that vegetables sleep always, is to use an 

 inaccurate and unmeaning expression. How can plants, without brain or nerves, with- 

 but organs of sense, motion, or voice, sleep ; when sleep is nothing but the repose of 

 these organs ? 



t The tissue of the eye-lids is not so opake but we may distinguish through them light 

 from darkness : accordingly, a lighted torch in the room, hinders us from sleeping. For 

 the same reason, day succeeding to night awakens us. 



