Above is a photo of my late father, taken in the 1950's in his physiotherapy treatment room (the front room of our house).
The large console on the right of which only half is in view, is an electrotherapy machine. I am fairly sure it was made by Electro Medical Supplies, a company that still exists as EMS Physio Ltd.
I emailed them a few years ago hoping to get a scan of a manual, or some contemporary marketing material about the machine, and I did get a nice reply, although nothing specifically about my dad's machine.
A similar, but older model, probably pre-war, was featured on Antiques Roadshow.
The recess in the centre of the console is covered by a glass door and behind it the mechanism that rhythmically surged the current. it consisted of a glass flask filled with saline solution and a motor and lever arrangement lowered and raised an electrode.