156 OF SLEEP. Sect. XVIII. 1 7. 



than diminifhed during thefe hours of our exiflence ; and it is 

 probable that nutrition is almoft entirely performed in fleep ; 

 and that young animals grow more at this time than in their 

 waking hours, as young plants have long fince been obferved to 

 grow more in the night, which is their time of fleep. 



17. Two other remarkable circumdances of our dreaming 

 ideas are their inconfiftency, and the total abfence of furprife. 

 Thus we feem to be prefent at more extraordinary metamor- 

 phofes uf animals or trees, than are to be met with in the fable9 

 of antiquity 5 and appear to be tranfported from place to place, 

 which feas divide, as quickly as the changes of fceaery are per- 

 formed in a play-houfe ; and yet are not fenfible of their in- 

 coniidency, nor in the lead degree affected with furprife. 



"We mult confuler this circumftance more minutely. In our 

 waking trains of ideas, thofe that are inconfident with the ufual 

 order of nature, fo rarely have occurred to us, that their con- 

 nexion is the flighted of all others : hence, when a confident 

 train of ideas is exhaufted, we attend to the external ftimuli, 

 that ufual ly furround us, rather than to any inconfiflent idea, 

 which might otherwife prefent itfelf : and if an incontinent 

 idea fl»ould intrude itfelf, we immediately compare it with the 

 preceding one, and voluntarily reject the train it would intro- 

 duce ; this appears further in the Section on Reverie, in which 

 ft ate of the mind external ftimuli are not attended to, and yet 

 the dreams of ideas are kept confident by the efforts of volition. 

 But as our faculty of volition is fufpended, and all external ftim« 

 \i!i are excluded in fleep, this {lighter connexion of ideas takes 

 place ; aud the train is faid to be inconfiflent ; that is, diffimi- 

 iar to the ufual order of nature. 



But, when any confident train of fenfitive or voluntary 

 ideas is flowing along, if any external dimulus affects us fo vio- 

 lently, as to intrude irritative ideas forcibly into the mind, it 

 difunites the former train of ideas, and we are affected withfur- 

 r.rifc. Thefe dimuli of unufual energy or novelty not only dil- 

 unite our common trains of ideas, but the trains of mufcular mo- 

 tions aifo, which have not been long edabliihed by habit, and 

 diiturb thofe that have. Some people become motionlefs by 

 great furprife, the fits of hiccup and of ague have been often re- 

 moved by it, and it even affects the movements of the heart, and 

 arteries \ but in our fleep, all external ftimuli are excluded, and 

 in confequence no furprife can exid. See Section XVII. 3. 7. 



18. We frequently awake with pleafure from a dream, which 

 has delighted us, without being able to recollect the tranfic- 

 tions of it j unlefs perhaps at a didance of time, fome analogous 

 idea m-ty introduce afrem this forgotten train : and in our wa- 

 king 



