SECT. XXXVI. i. PERIODS OF DISEASES. 515 



lingers, when any one hangs by his hands on a 

 iwing, fatigue foon enfu.es ; and the mufcl.es ccafe 

 to act, owing to the temporary exhauftion of the 

 fphit of animation ; as foon as this is again accu- 

 mulated in the mufcles, they are ready to contract 

 again by the efforts of volition. 



Thofe violent mufcular actions induced by pain 

 become in the fame manner intermitted and recur- 

 rent ; as in labour-pains, vomiting, tenefmus, ftran- 

 gury ; owing likcwife to the temporary exhauftion 

 of the fpirit of animation, as above mentioned. 



When any ftimulus continues long to act w r ith 

 unnatural violence, fo as to produce too energetic 

 action of any of our moving organs, thofe motions 

 foon ceafe, though the flimulus continues to act; 

 as in looking long on a bright object, as on an 

 jnch-fquare of red filk laid on white paper in the 

 jfunfhine. See Plate I. in Sect. IIL i. ' 



On the contrary, \vhere lefs of the flimulus of 

 volition, fenfation, or imitation, have been ap- 

 plied to a mufcle than ufual ; there appears to be 

 an accumulation of the fpirit of animation in the 

 jnoving organ ; by which it is liable to at with 

 greater energy from lefs quantity of flimulus, than 

 was previoufly neceflary to excite it into fo great 

 action ; as after having been imrnerfed in fnow the 

 cutaneous veffels of our hands are excited imp 

 ilronger action by the flimulus of a lefs degree of 

 heat, than would previously have produced that 

 effea. 



From hence the periods of fome fever-fits may 

 take their origin, either fimply, or by their acci- 

 dental coincidence with lunar and folar r.^riofls, or 

 with the diurnal periods of heat and cold, to be 

 treated of below ; for during the cold fit at the 

 commencement of a fever, from whatever caufe that 

 cold fit may be induced, it follows, i. That the 

 fpirit of animation muft become accumulated in 



the 



