SECT. XVIII. 2. OF SLEEP. 2F 7 



fions, but we never compare their objeh, or deli- 

 berate about the acquifition of thofe objects, if our 

 ileep is perfect. And though many fynchronous 

 tribes or fucceflive trains of ideas may reprefent the 

 houfes or walks, which have real exigence, yet are 

 they here introduced by their connection with our 

 fenfations, and are in truth ideas of imagination, 

 not of recollection. 



2. For our fenfations of pleafure and pain arc ex- 

 perienced with great vivacity in our dreams ; and 

 hence all that motley group of ideas, which are 

 caufed by them, called the ideas of imagination, 

 with their various alTociated trains, are in a very vi- 

 vid manner acted over in the fenforium ; and thefe 

 fometimes call into action the larger mufcles, which 

 have been much alTociated with them ; as appears 

 from the muttering featences, which fome people 

 utter in their dreams, and from the obfcure bark- 

 ing of fleeprng dogs, and the motions of their 

 feet and noftrils. 



This perpetual flow of the trains of ideas, which 

 conftitute our dreams, and which are caufed by 

 .painful or pleafurable fenfation, might at firfl view 

 be conceived to be an ufelefs expenditure of fen- 

 forial power. But it has been mewn, that thofe 

 motions, which are perpetually excited, as thofe of 

 the arterial fyftem by the ftimulus of the blood, are 

 attended by a great accumulation of fenforial power, 

 after they have been for a time fufpended ; as the 

 hot-fit of fever is the confequence of the cold one* 

 Now as thefe trains of ideas caufed by fenfation are 

 perpetually excited during our waking hours, if 

 they were to be fufpended in ileep like the voluntary 

 motions, (which are exerted only by intervals du- 

 ring our waking hours,) an accumulation of fenfo- 

 rial power would follow ; and on our awaking- a 

 delirium would fupervene, fince thefe ideas caufed 

 by fenfation would be produced with fuch energy, 



R 2 that 



