1 62 OF SLEEP. Sect. XVIII. i i 



j' 



fenfes are alfo alive and excitable in our fleep ; but as the ftimuli 

 of external objects are either excluded from them by the dark- 

 nefs and filence of the night, or their accefs to them is prevented 

 by the fufpenfion of volition, thefe nerves of fenfe fall more 

 readily into their connexions with fenfation and with afTociation ; 

 becaufe much fenforial power, which during the day was ex- 

 pended in moving the external organs of fenfe in confequence 

 of irritation from external ftimuli, or in confequence of volition, 

 becomes now in fome degree accumulated, and renders the in- 

 ternal or immediate organs of fenfe more eafily excitable by the 

 other fenforial powers. Thus in refpect to the eye, the irritation, 

 from external ftimuli, and the power of volition during our 

 waking hours, elevate the eyelids, adapt the aperture of the iris 

 to the quantity of light, the focus of the cryftalline humour, and 

 the angle of the optic axifes to the diflance of the object, all 

 which perpetual activity during the day expends much fenforial 

 power, which is faved during our fleep. 



Hence it appears, that not only thofe parts of the fyftem, 

 which are always excited by internal ftimuli, as the ftomach, 

 inteftinal canal, bile-ducts, and the various glands, but the or- 

 gans of fenfe alfo may be more violently excited into action by 

 the irritation from internal ftimuli, or by fenfation, during our 

 fleep thiin in our waking hours; becaufe during the fufpenfion 

 of volition, there is a greater quantity of the fpirit of animation 

 to be expended by the other fenforial powers. On this account 

 our irritability to internal ftimuli, and our fenfibility to pain or . 

 pleafure, is not only greater in fleep, but increafes as our fleep 

 is prolonged. Whence digeftion and fecretion are performed 

 better in fleep, than in our waking hours, and our dreams in the 

 morning have greater variety and vivacity, as our fenfibility inj 

 creafes, than at night when we firft lie down. And hence epi- 

 leptic fits, which are always occafioned by fome difagreeable fen- 

 fation, fo frequently attack thofe, who are fubjecl to them, in 

 their fleep ; becaufe at this time the fyftem is more excitable by 

 painful fenfation in confequence of internal ftimuli ; and the 

 power of volition is then fuddenly exerted to relieve this pain, 

 as explained Seel:. XXXIV. i. 4. 



There is a difeafe, which frequently affects children in the 

 cradle, which is termed ecftafy, and feems to confift in certain 

 exertions to relieve painful fenfation, in which the voluntary 

 power h not fo far excited as totally to awaken them, and yet is 

 fumcient to remove the difagreeable fenfation, which excites 

 in this cafe changing the pofture of the child frequently 



lieves it. 



I have at this time under my care an elegant young *mart 



about 



