448 INFLUENCE OF NERVES ON MUSOLES. 
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it is completely withdrawn from the dominion of the nervous 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 
