46 OF STIMULUS Sect. XII. i. 2. 



of the elaftic gum to depend more on the refiftance to the lateral 

 compreffion of its particles than to the longitudinal extenfion of 

 them. Neverthelefs in mufcular contraction, as above observ- 

 ed, there appears no difference in the velocity or force of it at 

 its commencement or at its termination ; from whence we muft 

 conclude that animal contraction is governed by laws of its own, 

 and not by thofe of mechanics, chemiftry, magnetifm, or elec- 

 tricity. 



On thefe accounts I do not think the experiments conclufive, 

 which were lately publifhed by Galvani, Volta, and others, to 

 (hew a fimilitude between the fpirit of animation, which con- 

 tracts the mufcular fibres, and the electric fluid. Since the 

 electric fluid may act only as a more potent Itirnulus exciting 

 the mufcular fibres into action, and not by fupplying them with 

 a new quantity of the fpirit of life. Thus in a recent hemiple- 

 gia I have frequently obferved, when the patient yawned and 

 ftretched himfelf, that the paralytic limbs moved alfo, though 

 they were totally difobedient to the will. And when he was 

 electrified by palling fhocks from the affected hand to the affect- 

 ed foot, a motion of the paralytic limbs was alfo produced. Now 

 as in the act of yawning the mufcles of the paralytic limbs were 

 excited into action by the flimulus of the irkfomenefs of a con- 

 tinued pofture, and not by any additional quantity of the fpirit 

 of life ; fo we may conclude, that the paffage of the electric flu- 

 id, which produced a fimilar effect, acted only as a flimulus, 

 and not by fupplying any addition of fenforial power. 



If neverthelefs this theory fhould ever become eltablifhed, a 

 flimulus muft be called an eductor of vital ether ; which flim- 

 ttlus may confift of fenfation or volition, as in the electric eel, as 

 well as in the appulfer> of external bodies ; and by drawing off 

 the charges of viral fluid may occafion the contraction or mo- 

 tions of the mufcular fibres, and organs of fenfe. 



2. The immediate effect of the action of the fpirit of anima- 

 tion or fenforial power on the fibrous parts of the body, whether 

 it acts in the mode of irritation, fenfation, volition, or affocia- 

 tion, is a contraction of the animal fibre, according to the fec- 

 ond law of animal caufation. Sect . IV. Thus the flimulus of 

 the blood induces the contraction of the heart ; the agreeable 



.:e of a (Ira ;v berry produces the contraction of the mufcles of 

 deglutition ; the effort of the will contrails the mufcles, which 

 f e limb", in walking \ and by affociation other mufcles of 



' 5 tru ought into contraction to preferve the balance 



of the L- The fibrous extremities of the organs of fenfe 



:wn, : he ocular fpectra in Sect III. to fuller 



fimila* 



