[ 198 ] 



SECT. XX 



OF SLEEP. 



317. THE faculties both of feeling and motion, pos- 

 sessed by the nervous system whose history we have 

 thus pursued, are so fatigued by their exertions in the 

 day, that rest is necessary during the night to recruit 

 them by means of sleep * the image of death. 



318. Sleep is a periodical function, by which the 

 intercourse of the mind and body is suspended, and 

 whose phenomena, now to be traced, correspond very 

 aptly with the supposition of a nervous fluid. 



319 Besides other precursors of sleep, may be enu- 

 merated a gradually increasing dulness of the external 

 senses, and a relaxation of most, especially of the long, 

 voluntary muscles ; a congestion of venous blood about 

 the heart, and relief afforded by yawning to the uneasy 

 sensation thus produced ; lastly, a curious kind of short 

 delirium at the moment when sleep is all but present.f 



320. The phenomena of sleep, therefore, amount to 

 this, that the animal functions are suspended, and all 

 the rest proceed more slowly and inactively. For the 

 pulse is slower, the animal heat, creteris paribus, dimi- 

 nished, perspiration more sparing, digestion imperfect, 



* Consult, among authors hereafter to be recommended, Er. Darwin, Zoo- 

 twinia. T. i. Sect, xviii. 



-'r De Pauw has some singular observations upon it in his Richer dies >< Us 

 ct les Chinois. T- ji- p. l">y. 



