94 OF STIMULUS AND EXERTION. SECT. XII 5. 



the fame manner to the too great exhauftion of 

 the fpirit of animation in the affected part ; fo that 

 a ftronger ftimulus is required, or one of a different 

 kind from that, which occafioned thofe too violent 

 contractions, to again excite the affected organ 

 into activity ; and if a ftronger ftimulus could be 

 applied, it muft again induce paralyfis. 



For theie powerful ftimuli excite pain at the fame 

 time, that they produce irritation ; and this pain 

 not only excites fibrous motions by its ftimulus, 

 but it alfo produces volition ; and thus all thefe 

 ftimuli acting at the fame time, and fometimes with 

 the addition of their aflbciations, produce fo great 

 exertion as to expend the whole of tire fenforial 

 power in the affected fibres. 



V. Of Stimulus lefs than natural. 



i. A quantity of ftimulus lefs than natural, pro- 

 ducing a decreafed exertion of fenforial power, oc- 

 cafions an accumulation of the general quantity of 

 it. This circumftance is obfervable in the hemi- 

 plagia, in which the patients are perpetually moving 

 the mufcles, which are unaffected. On this ac- 

 count we awake with greater vigour after fleep, 

 becaufe during fo many hours, the great ufual ex- 

 penditure of fenforial power in the performance of 

 voluntary actions, and in the exertions of our or- 

 gans of fenfe, in confequence of the irritations oc- 

 cafioned by external objects, had been fufpended, 

 and a confequent accumulation had taken place. 



In like manner the exertion of the fenforial 

 power lefs than natural in one part of the fyftem, 

 isliabls to produce an increafe of the exertion of it 

 in fome other part. Thus by the action of vomit- 

 ing, in which the natural exertions of the motions 

 of the ftomach are deiiroyed or dirmniihed, an in- 



creafed 



