SECT. XVIIL 15. OF SLEEP. 161 



brought into aftion to remove that irritation or fenfation, which 

 a continued pofture has caufed ; we ftretch our limbs, and 

 yawn, and our ileep is thus broken by the accumulation of vol- 

 untary power. 



Sometimes it happens, that the aft of waking is fuddenly pro- 

 duced, and this foon after the commencement of ileep ; which 

 is occafioned by fome fenfation fo difagreeable, as inftantane- 

 oufly to excite the power of volition ; and a temporary action of 

 all the voluntary motions fuddenly fucceeds, and we ftart awake. 

 This is fometimes accompanied with loud noife in the ears, and 

 with fome degree of fear ; and when it is in great excefs, fo as 

 to produce continued convulfive motions of thofe mufcles, 

 which are generally fubfervient to volition, it becomes epilepfy ; 

 the (its of which in fome patiems generally commence during 

 ileep. This differs from the nightmare defcribed in No. 3. of 

 this Section, becaufe in that the difagreeable fenfation is not fo 

 great as to excite the power of volition into adion ; for as foon 

 as that happens, the difeafe ceafes. 



Another circumftance, which fometimes awakes people foon 

 after the commencement of their fleep, is where the voluntary 

 power is already fo great in quantity as almoft to prevent them 

 from falling afleep, and then a little accumulation of it foon 

 again awakens them ; this happens in cafes of infanity, or 

 where the mind has been lately much agitated by fear or anger. 

 There is another circumftance in which fleep is likewife of 

 iliort duration, which arifes from great debility, as after great 

 over- fatigue, and in fome fevers, where the flrength of the 

 patient is greatly diminifhed : as in thefe cafes the pulfe inter- 

 mits or flutters, and the refpiration is previoufly affected, it 

 feems to originate from the want of fome voluntary efforts to 

 facilitate refpiration, as when we are awake, and is further 

 treated of in Vol. II. Clafs I. 2. i. 2, on the Difeafes of the 

 Voluntary Power Art. Somnus interruptus. 



15. We come now to thofe motions which depend on irrita- 

 tion. The motions of the arterial and glandular fyftems con- 

 tinue in our fleep, proceeding flower indeed, but ftronger and 

 more uniformly, than in our waking hours> when they are in- 

 commoded by external ftimuli, or by the movements of volition ; 

 the motions of the mufcles fubfervient to refpiration continue 

 to be ftimulated into action, and the other internal fenfes of hun- 

 ger, thirft, and luft, are not only occailonally excited in our fleep, 

 but their irritative motions are face-ceded by their ufual fenfa- 

 tions, and make a part of the farrago of our dreams. Thefe 

 fenfations of the want of air, of hunger, thirft, and luft, in our 

 dreams, contribute to prove, that the nerves of the external 

 VOL. I. X fenfes 



