Maybe it was a prehistoric Galvani doing the original frog leg jumping experimet. :)
To me, they look like Galvanic cells, despite the lack of a connection to the tube. And almost any ion-bearing solution (electrolyte will work. Even the LeClanche cell (the common carbon-zinc "battery") uses ammonium chloride as an electrolyte.
Seems like a simpler explanation than the rotten documet storage notion.
Of course, there's always the oft-used shotgun explanation that it was a religious artifact.
That always works.
Terry, 230RN