48a DISEASES OF VOLITION. SECT. XXXIV. i. 



ver exift in a great degree or univerfally at the 

 fame time ; for while we ilrongly exert our volun- 

 tary motions, we ceaie to feel the pains or uneafi- 

 nefles, which occafioned us to exert them. 



Hence during the time of fighting with fids or 

 fwords no pain is felt by the combatants, till they 

 ceafe to exert themfelves. Thus in the beginning 

 of ague fits the painful fenfation of cold is dimi- 

 nifhed, while the patient exerts himfelf in the fhi- 

 vering and gnafhing of his teeth. He then ceafes 

 to exert himfelf, and the pain of cold returns ; and 

 he is thus perpetually induced to reiterate thefe 

 exertions, from which he experiences a temporary 

 relief. The fame occurs in labour-pains, the exer- 

 tion of the parturient woman relieves the violence 

 of the pains for a time, which recur again foon after 

 fhe has ceafed to ufe thofe exertions. The fame 

 is true in many other painful difeafes, as in the 

 ftrangury, tenefmus, and the efforts of vomiting ; all 

 thefe difagreeable fenfations are diminifhed or re- 

 moved for a time by the various exertions they 

 occafioo, and recur alternately with thofe exerti- 

 ons. 



The reftleffnefs in fome fevers is an almoft perpe- 

 tual exertion of this kind, excited to relieve fome 

 difagreeable fenfations ; the reciprocal oppofite exer- 

 tions of a wounded worm, the alternate emproftho- 

 tonos and opifthotonos of fome fpafmodic difeafes, 

 and the intervals of all convulfions, from whatever 

 caufe, feem to be owing to this circumflauce of the 

 laws of animation ; that great or univerfal exertion 

 cannot exift at the fame time with great or uni- 

 verfal fenfation, though they can exift reciprocally ; 

 which is probably refolvable into the more general 

 law, that the whole ienforial power being expended 

 in one mode of exertion, there is none to fpare for 

 any other. Whence fyncope, or temporary apo- 

 plexy, fucceeds to epileptic convulfions. 



3. Hence 



