Chap.V. ANTIENT METAPHYSICS. 239 



Sleep, therefore, Is a temporary incapacity of the Co?7imon Senfo- 

 r/«;;/, or Senfitive Part of our Mind, to perceive the impreffions made 

 upon the feveral Organs of Senfe, by external objedsj I fay tem" 

 forary Incapacity^ becaufe, if we fuppofe a perpetual incapacity, 

 then fuch a Body would not be an Animal, but a Vegetable, or feme 

 Inanimate Subftance. And as what never a£ls, mufl: be fuppofed 

 not to have the capacity of a£bing, which, in that cafe, would be 

 to no purpofe ; therefore all Animals, according to Ariftotle, muft, 

 at times, wake as well as fleep ; that is, at fome time or another^ 

 they muft have the ufc and exercife of one Senfe at leaft *. 



Thus, one lliould think that Sleeping was fufficiently diftinguifhed 

 from Waking : But it is not fo ; for, as Ariftotle has obferved, there 

 are temporary incapacities of perception by Senfe, which are not 

 Sleep, becaufe they proceed from difeafe, or from fome hurt. And he 

 inftances Fainting, in which we have no perception by Senfe, and yet 

 fee wonderful Phantafms f. The temporary incapacity, therefore, 

 of Senfation, properly called Sleep, is that which proceeds from Na- 

 ture, not from Accident or Difeafe ; for, as Ariftotle informs us, 

 the Operations of Mind, by means of the Body, fuch as Senfation, 

 cannot, by their nature, be perpetual ; and, therefore, when they 

 are continued for a certain time, the Senforium becomes wearied, as 

 it were, and incapable to perform its functions, and then the Ani- 

 mal falls afleep. And this, according to Ariftotle, produces the ne- 

 ceflity of Sleep in all Animals \. The Final Caufe, therefore, of 

 Sleep, according to him, is the relaxation and refrefliment of the 

 Animal, while the Senfes are locked up : And the Efficient and 

 Material Caufe is certain Vapours, which, he fays, arife from the 



nourifti- 



• Ibid cap. I. 



t Ibid. cap. 3. in initio. See an extiaordlnary fact of/ iliis kind, mentioned 

 page 224. 



± Ibid. cap. 3. 



