What do you notice about the number of atoms of each element on the reactant and

The equivalent circuit for the electrode while the electrolyte gel is fresh

From the uploaded diagram the part A is the electrolyte, the part part B is the electrolyte gel when is fresh and the part C is the surface of the skin

Now as the electrolyte gel start to dry out the resistance of the gel begins to increase and this starts to limit the flow of current . Now when the gel is then completely dried out  the resistance of the gel then increases to infinity  and this in turn cut off flow of current.

The diagram illustrating this is shown on the second uploaded image

Explanation: