They didn't actually "turn it off". There was a gauze mask they put over your nose and mouth, then they sprinkled ether on the mask from a can. If you started going down too deep, they'd just lift the mask away from your face. I suppose they had oxygen available if they needed it.
The first time I had surgery, they used ether to put me under in just the way I described. The anesthesiologist told me to start counting backwards from 100, and started sprinkling on the ether. I was out by ninety. My father was waiting down the hall, and he said he could hear my breathing all the way down there while I was under the ether.
I had the most bizzarre dream while under the ether. It was all sirens and firetrucks, in vivid color and surround sound (my dreams are normally in black and white, with crappy sound). Don't know why, but I still remember it vividly 50 years later.
Gary