448 INFLUENCE OF NERVES ON MUSCLES. 



peculiar operation ( 423). But there are many objections to 

 such a view ; and it appears more correct to regard Electricity 

 and Nerve-force as correlated, that is, as each capable, under 

 certain conditions, of exciting an equivalent measure of the 

 other, than to consider them as identical. 



586. The power, whatever be its nature, by which the 

 Nerves act upon the Muscles in the living body, originates 

 in the central organs, or ganglionic masses, of the nervous 

 system ; and is propagated from these, through the nervous 

 fibres, to the muscles, in a mode precisely analogous to that 

 in which the electric power, called-forth by the action of an 

 electrical machine or galvanic battery, is transmitted to any 

 distance through conducting wires. If the conductor be 

 divided, no action at the centre, however powerful, can pro- 

 duce any change at its extremities ; and in this manner, by 

 division of the nervous trunk, the muscle supplied by it is 

 palsied. The muscle itself does not thereby lose its contrac- 

 tility; for it may still be made to contract by a stimulus 

 transmitted through the part of the trunk that remains 

 attached to it, as, for instance, by pricking or pinching the 

 cut extremity, or by passing an electric current along it ; but 

 it is completely withdrawn from the dominion of the nervous 

 centres under which it previously was ; and cannot be called 

 into action either by the will, by an emotion, or by a reflex 

 impulse. The part of the trunk in connexion with it soon 

 loses its power of conveying irritations ; and the muscle itself 

 being thrown into disuse, in time loses its contractility. 



587. From this last fact it has been supposed that the 

 contractility of muscular fibre depends upon its connexion 

 with the nervous system, and is not an endowment peculiar 

 to itself. But this idea is disproved by a number of circum- 

 stances. Thus the contractility of the heart and intestinal 

 tube is exhibited, long after these parts have been separated 

 from their nerves. The contractility of other muscles may be 

 exhausted by repeated excitement, so that even the stimulus 

 of galvanism will not produce movement in them ; and yet it 

 may be recovered after the nervous trunks have been divided. 

 And it has been ascertained that if the muscles be frequently 

 exercised, as by the application of galvanism once or twice a 

 day, they will retain their contractility for any length of time. 

 This exercise is further found to have the effect of preventing 



