Few of these have been put into use, for the reason that a switchboard, like a human body, must be semi-automatic only.

To give the most efficient service, there will always need to be an expert to stand between it and the public.
As the final result of all these varying changes in switchboards and signals and batteries, there grew up the modern Telephone Exchange.

This is the solar plexus of the telephone body.

It is the vital spot.

It is the home of the switchboard.