2 5$ OF SLEEP. SECT. XVIII. 23, 



we are employed about, the more violent muft be 

 the ftimulus that interrupts them, and the greater is 

 the degree of furprife. I have obferved dogs, who 

 have flept by the fire, and by their obfcure barking and 

 ftruggling have appeared very intent on their prey, 

 that (hewed great furprife for a few feconds after 

 their awaking by looking eagerly about them ; which 

 they did not do at other rimes of waking. And an 

 intelligent friend of mine has remarked, that his 

 lady, who frequently fpeaks much arid articulately 

 in her fleep, could never recollect her dreams in the 

 morning, when* this happened to her: but that 

 when me did not fpeak in her fleep, fhs could always 

 recoiled them, 



Hence, when our fenfations aft fo ftrongly in fleep 

 as to influence the larger mufcles, as in thofe, who 

 talk or ftruggle in their dreams ; or in thofe, who 

 are affected with complete reverie (as defcribed in 

 the next Section), great furprife is produced, when 

 they awake ; and 'thefe, as well as thofe who are 

 completely drunk or delirious, totally forget after- 

 wards their imaginations at thofe times. 



20. As the immediate caufe of fleep confifls in 

 the fufpenfion of volition, it follows, that whatever 

 diminilhes the general quantity of fenforial power, or 

 derives it from the faculty of volition, will con- 

 Ititute a remote caufe of fleep ; fuch as fatigue from 

 mufcular or mental exertion, which diminifhes the 

 general quantity of fenforial power ; or an increafe 

 of the fenfitive motions, as by attending to foft mufic, 

 which diverts the fenforial power from the faculty of 

 volition ; or laftly, by increafe of the irritative mo- 

 tions, as by wine,, or food, or warmth ; which not 

 only by their expenditure of fenforiai power dimi- 

 riifri the quantity of volition ; but alfo by their pro- 

 ducing pleafurable fenfations (which occafion other 

 inufcuiar or fenfual motions in confequence), doubly 

 decreafe the voluntary power, and thus more forcibly 

 produce fleep. See Seel. XXXIV. 1.4. 



Another 



