Sect. XVIII. i^ OF SLEEP, if* 



brought into ac~lion to remove that irritation or fenfation, which 

 a continued pofture h2S caufed ; we ftretch our Iknibs, and 

 yawn, and our fleep is thus broken by the accumulation of voU 

 untary power. 



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

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

 is occafioncd by fome fenfation fo difagreeabie, as iuitantane- 

 oufly to excite the power of volition 5 and a temporary action 01 

 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 excels, lb as 

 to produce continued convulfive motions of thole mufcles^ 

 which are generally fubfervient to volition, it becomes epilepfy : 

 the fits of which in fome patients generally commence during 

 fleep. This differs from the nightmare defcribed in No. 3. o£ 

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

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

 as that happens, the difeafe ceafes. 



Another circumftance, which fometimes awakes people foert 

 after the commencement of their fleep, is where the voluntary- 

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

 from falling alleep, 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 

 iiiort duration, which ariies from great debility, as after great 

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

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

 mits of flutters, and the refpiration is previouily 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. 1. 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 flimuJi, or by the movements of volition ; 

 the motions of the mufcles fubfervient to refpiration continue 

 to be flimulated into action, and the other internal fenies of hun- 

 ger, thivft, and kill, are not only occafionally excited in our fleep, 

 but their irritative motions are fucceeded by their uiual folia- 

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

 fenfations of the want of air, of hunger, thirft, and lu^t, in our 

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



Vo l. I. A fei . 



