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38 The nerve-current sets free the energy already stored in the muscle. The muscle substance is a magazine or store of energy, and this energy is set free by the molecular action of the nerve.

Having got hold of these general notions as

to how a nerve acts on a muscle, let us consider for a little the nature of the electric shocks we employ for stimulating the nerve.

I have here a number of galvanic elements joined together so as to constitute what we term a battery. Electricity is generated in these elements in consequence of chemical changes occurring in them, and we may suppose this electricity to flow like a current out by this wire, along any circuit formed by a