Found this Sammy Baugh quote in the new book, Slingin' Sammy'.. and it does put some perspective on the pass defenses of 1935:
They did some things I hadn’t seen before. They’d throw up a six-man line with two linebackers, so they had eight guys pretty close to the front. If they all came, they had a pretty good pass rush, but you had to call your blocking for six men coming. Sometimes the linebackers would come, but someone else would drop back. They usually had four men protecting that short, eight-or nine-yard area, But we never knew which ones.
Sorry, but those who think the zone blitz originated in the 1970s are at least 35 years too late.
I have other observations of this ilk in my latest blog post here (yes, shameless plug..)