4 OF STIMULUS SECT. XII. 1.2, 



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

 comprelTion of its particles than to the longitudinal extcnfion of 

 them. Neverthelefs in mufcular contraction, as above obferv- 

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

 its commencement or at its termination j from whence we mull 

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

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

 tricity. 



On thele accounts I do not think the experiments conclufive, 

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

 {hew a ilmilitude between the fpirit of animation, which con- 

 trafts the mufcular fibres, and the eledric fluid. Since the 

 eledlric fluid may at only as a more potent itimulus 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 

 itretched himfeif, that the paralvtic limbs moved alfo, though 

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

 electrified by palling (hocks from the affected hand to the affedt- 

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

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

 excited into action by the ftimulus 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 paffuge of the eledtrk: flu- 

 id, which produced a fimilar effect, adted only as a llimulus, 

 and not by fupplying any addition of fenforial power. 



If neverthelefs this theory fhould ever become eftablifhed, a 

 ftimulus mult be called an edudor of vital ether , which ftim- 

 ulus may confift of fen fat ion or volition, as in the electric eel, as 

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

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

 tions of the mufcular fibres, and organs of fenfe. 



2. The immediate effort of the adlion of the fpirit of anima- 

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

 it a<5ts 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. Seft. IV. Thus the ftimulus of 

 the blood induces the contraction of the heart ; the agreeable 

 tafte of a ftrawberry produces the contraction of the mufcles of 

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

 move the limbs in walking j and by affociation other mufcles or 

 the trunk are brought into contraction to preferve the balance 

 of the body. The fibrous extremities of the organs of fenfe 

 have been ihewn, by the ocular fpeftra in Sect. III. to fuffer 



fimilar 



