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heat, by acids and alkalies, and by several other chemical and medi- 

 cinal substances, until the possibility of provoking contraction by the 

 touch of a needle has been destroyed by the action of the agent 

 until, that is to say, the " irritability " of the nerve has been de- 

 stroyed by this action (Eckardt); and (4) because the influence of 

 the nervous centre in causing contraction is to suspend the natural 

 electricity of the nerve and muscle. This last conclusion is evident 

 in the fact, that the signs of electricity, which are absent during 

 tetanus, immediately reappear in the muscle and in the portion of 

 nerve connected with it, when the influence of the nervous centre is 

 cut off and the tetanus resolved by dividing the nerve. 



(6.) That blood cannot cause contraction, (1) because the tendency 

 to contraction is inversely related to the supply of blood ; thus, this 

 tendency is greater in the voluntary muscles of fishes and reptiles 

 than of mammals and birds greater in involuntary than in volun- 

 tary muscles greater in the muscles of any given animal during the 

 state of hybernation than during the period of summer life ; and 

 (2) because the state of rigor mortis may be relaxed more than 

 once, and the lost " irritability " restored to the muscle by the in- 

 jection of living blood into the vessels (Brown- Seguard). 



(c.) That electricity cannot cause contraction, (1) because there is 

 a constant current of electricity in a muscle during rest, but not 

 during contraction (Du Bois Reymond), because, that is to say, 

 contraction is absent when muscle is in a state of electrical or polar 

 action, and present when this state is absent, so that contraction ap- 

 pears to be antagonized by this state of polar action; and (2) because 

 contraction is never coincident with the passage of a current of arti- 

 ficial electricity ; for, not only is it true that a muscle does not con- 

 tract during the time that a current of artificial electricity is passing 

 through it, but contraction is invariably relaxed if contraction pre- 

 existed (Eckardt). There is, indeed, momentary contraction at the 

 opening or at the closing of the circuit, but this contraction can be 

 shown to be coincident with neutralization of electrical action, 

 which neutralization is consequent upon the momentary opposition 

 of the natural current of the muscle and the artificial current. 



(rf.) That mechanical agents cannot stimulate contraction, (1) be- 

 cause the electrical phenomena of muscle are opposed to such an 

 idea ; thus muscle affords evidences of electricity during rest, but 



