Indeed and didn't Mr Kellogg make a big thing out of it (no pun intended)? Enough to put you off your cornflakes.
I remember reading about it, described as 'self abuse', in my uncle's medical encyclopaedia which said the habit caused weakness in the legs, depression and urination problems, and that adults should be alert to signs, such as uncharacteristic quietness and wanting to spend a lot of time alone in room - but it didn't describe exactly what it was young men - and some young women - did. As a child, I was intrigued but couldn't ask anyone.