50 OF STIMULUS Sect. XII. t. 7, 



introduces pleafurable fenfation into the fyftem, according to the 

 fourth law of animal caufation. Hence the pleafure in the be- 

 ginning of drunkennefs is owing to the increafed action of the 

 fyftem from the fiimulus of vinous fpirit or of opium. If the 

 contractions be fiill greater in energy or duration, painful fen- 

 fations are introduced, as in confequence of great heat, or cauf- 

 tic applications, or fatigue. 



If any part of the fyftem, which is ufed to perpetual activity, 

 as the ftomach, or heart, or the fine veflels of the fkin, ads for a 

 time with lefs energy, another kind of painful fenfation enfues, 

 which is called hunger, or faintnefs, or cold. This occurs in a 

 lefs degree in the locomotive mufcles, and is called wearifome- 

 nefs. In the two former kinds of fenfation there is an expendi- 

 ture of fenforial power, in thefe latter there is an accumulation 

 Of it. 



7. We have ufed the words exertion of fenforial power as a 

 general term to exprefs either irritation, fenfation, volition, or 

 affociation ; that is, to exprefs the activity or motion of the fpirit 

 of animation, at the time it produces the contractions of the 

 fibrous parts of the fyftem. It may be fuppofcd that there may 

 exift a greater or lefs mobility of the fibrous parts of our fyftem, 

 or a propensity to be ftimulated into contraction by the greater 

 or lefs quantity or energy of the fpirit of animation ; and that 

 hence if the exertion of the fenforial power be in its natural 

 Hate, and the mobility of the fibres be increafed, the fame quan- 

 tity of fibrous contraction will be caufed, as if the mobility of 

 the fibres continues in its natural ftate, and the fenforial exertion 

 be increafed. 



Thus it may be conceived, that in difeafes accompanied with, 

 ftrength, as in inflammatory fevers with arterial ftrcngth, that 

 the caufe of greater fibrous contraction may exift in the increaf- 

 ed mobility of the fibres, whofe contractions are thence both 

 more forcible and more frequent. And that in difeafes attended 

 with debility, as in nervous fevers, where the fibrous contrac- 

 tions are weaker, and more frequent, it may be conceived that 

 the caufe confifts in a decreafe of mobility of the fibres ; and 

 that thofe weak conftitutions, which are attended with cold 

 extremities and large pupils of the eyes, may poiTefs lefs mobil- 

 ity of the contractile fibres, as well as lefs quantity of exertion 

 of the fpirit of animation. 



In anfwer to this mode of reafoning it may be fufBcient to ob- 

 ferve, that the contractile fibres confift of inert matter, and 

 when the fenforial power is withdrawn, as in death, they pofTefs 

 no power of motion at all, but remain in their laft ftate, whether 

 of contraction or relaxation, and muft thence deiive the whole 



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